Combining Multiple Images with Enblend 4.2

# Combining Multiple Images with Enblend 4.2

### 2016-03-292

This manual is for Enblend version ⟨4.2⟩, a tool for compositing images in such a way that the seam between the images is invisible, or at least very difficult to see.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.

# Contents

Chapters or sections marked with a “c”-sign appear in both manuals, i.e. the Enblend manual and the Enfuse manual. The commonality extends to all sub-sections of the marked one.

## Frontmatter A  Notation

This manual uses some typographic conventions to clarify the subject. The markup of the ready-to-print version differs from the web markup.

 Category Description Examples Acronym Common acronym sRGB, OpenMP Application GUI or CLI application Hugin, Enblend Command Name of a binary in the running text convert, enblend Common part Chapter, section, or any other part that appears in both manuals Response Filesc Default Value as compiled into the enblend binary that belongs to this documentation ⟨1⟩, ⟨a.tif⟩ Environment variable Variable passed to enblend by the operating system PATH, TMPDIR Filename Name of a file in the filesystem a.tif Filename extension Name of a filename extension with or without dots .png, tiff Fix me! Section that needs extending or at least some improvement FIXExplainME Literal text Text that (only) makes sense when typed in exactly as shown uint16 Option Command-line option given to enblend --verbose Optional part Optional part of a syntax description in square brackets --verbose [=LEVEL] Placehoder Meta-syntactic variable that stands in for the actual text ICC-PROFILE Proper name Name of a person or algorithm Dijkstra Restricted note Annotation that applies only to a particular program, configuration, or operating system Enblend. Sample Literal text in quotes ‘%’ or ‘--help’ Side note Non-essential or “geeky” material Gory details White space Indispensable white space r␣g␣b

# Chapter 1  Overview

Enblend overlays multiple images using the Burt-Adelson multi-resolution spline multi-resolution spline algorithm.1 This technique tries to make the seams between the input images invisible. The basic idea is that image features should be blended across a transition zone proportional in size to the spatial frequency of the features. For example, objects like trees and windowpanes have rapid changes in color. By blending these features in a narrow zone, you will not be able to see the seam because the eye already expects to see color changes at the edge of these features. Clouds and sky are the opposite. These features have to be blended across a wide transition zone because any sudden change in color will be immediately noticeable.

Enblend expects each input file to have an alpha channel. The alpha channel should indicate the region of the file that has valid image data. Enblend compares the alpha regions in the input files to find the areas where images overlap. Alpha channels can be used to indicate to Enblend that certain portions of an input image should not contribute to the final image.

Enblend does not align images. Use a tool such as Hugin or PanoTools to do this. The TIFF files produced by these programs are exactly what Enblend is designed to work with. Sometimes these GUIs allow to select feathering for the edges the images. This treatment is detrimental to Enblend. Turn off feathering by deselecting it or setting the “feather width” to zero.

Enblend blends the images in the order they are specified on the command line. You should order your images according to the way that they overlap, for example from left-to-right across the panorama. If you are making a multi-row panorama, we recommend blending each horizontal row individually, and then running Enblend a last time to blend all of the rows together vertically. The input images are processed in the order they appear on the command line. Multi-layer images are processed from the first layer to the last before Enblend considers the next image on the command line. Consult Section 4.5 on how to change the images’ order within multi-layer image files.

Find out more about Enblend on its SourceForge web page.

1
Peter J. Burt and Edward H. Adelson, “A Multiresolution Spline With Application to Image Mosaics”, ACM Transactions on Graphics, Vol. 2, No. 4, October 1983, pages 217–236.

# Chapter 2  Known Limitations

Enblend has its limitations. Some of them are inherent to the programs proper others are “imported” by using libraries as for example VIGRA. Here are some of the known ones.

• The BigTIFF image format is not supported.
• Total size of any – even intermediate – image is limited to 231 pixels, this is two giga-pixels.

• Each “next” image must overlap with the result of the blending of all previous images. In special occasions option ‘--pre-assemble’ can circumvent this sequential-blending restriction.
• No pair of images must overlap too much. In particular, no two images must be identical.
The overlap is exclusively defined by the masks of the overlapping images. This is exactly what the input masks are built for. Let A be the number of pixels that overlap in both masks. We use A as a measure of the overlap area – something 2-dimensional; technically it is a pixel count.

Construct the smallest circumscribed, par-axial rectangle of the overlap area. The rectangle has a circumference

 U = 2 (a + b),

which is of course 1-dimensional. Internally U again is a number of pixels just as A.

The threshold when we consider a pair of images sufficiently different is when A is larger than 2 times the number of pixels on the circumference U

 A > ⟨2⟩ × U.

Avoiding the term “fractal dimension”, we have constructed a simple measure of how 2-dimensional the overlap area is. This way we steer clear of feeding later processing stages with nearly 1-dimensional overlap regions, something that wreaks havoc on them.

• Option ‘--wrap=both’ performs blending in E(1) × E(1), which is only locally isomorphic to S(2). This will cause artifacts that do not appear in S(2). Enblend cannot blend within S(2).

# Chapter 3  Photographic Workflowc

Enblend and Enfuse are parts of a chain of tools to assemble images.

• Enblend combines a series of pictures taken at the same location but in different directions.
• Enfuse merges photos of the same subject at the same location and same direction, but taken with varying exposure parameters.

## 3.1  Standard, All-In-One Workflow

Figure 3.1 shows where Enblend and Enfuse sit in the tool chain of the standard workflow.

Take Images
Take multiple images to form a panorama, an exposure series, a focus stack, etc.…

There is one exception with Enfuse when a single raw image is converted multiple times to get several – typically differently “exposed” – images.

Exemplary Benefits:

• Many pictures taken from the same vantage point but showing different viewing directions. – Panorama
• Pictures of the same subject exposed with different shutter speeds. – Exposure series
• Images of the same subject focused at differing distances. – Focus stack

Remaining Problem: The “overlayed” images may not fit together, that is the overlay regions may not match exactly.

Convert Images
Convert the raw data exploiting the full dynamic range of the camera and capitalize on a high-quality conversion.
Align Images
Align the images so as to make them match as well as possible.

Again there is one exception and this is when images naturally align. For example, a series of images taken from a rock solid tripod with a cable release without touching the camera, or images taken with a shift lens, can align without further user intervention.

This step submits the images to affine transformations.

If necessary, it rectifies the lens’ distortions (e.g. barrel or pincushion), too.

Sometimes even luminance or color differences between pairs of overlaying images are corrected (“photometric alignment”).

Benefit: The overlay areas of images match as closely as possible given the quality if the input images and the lens model used in the transformation.

Remaining Problem: The images may still not align perfectly, for example, because of parallax errors, or blur produced by camera shake.

Combine Images
Enblend and Enfuse combine the aligned images into one.

Benefit: The overlay areas become imperceptible for all but the most misaligned images.

Remaining Problem: Enblend and Enfuse write images with an alpha channel; for more information on alpha channels see Chapter 8. Furthermore, the final image rarely is rectangular.

Post-process
Post-process the combined image with your favorite tool. Often the user will want to crop the image and simultaneously throw away the alpha channel.
View
Print
Enjoy

In the usual workflow Enblend and Enfuse generate the blending and fusing masks according to the command-line options and the input images including their associated alpha-channels, and then they immediately use these masks for multi-resolution blending or multi-resolution fusing the output image.

Sometimes more control over the masks is wanted. To this end, both applications provide the option pair --load-masks and --save-masks. See Chapter 4, for detailed explanations of both options. With the help of these options the processing can be broken up into two phases:

Avoid option --output here unless the blended or fused image at this point is wanted.

Neither application (re-)generates any mask in this phase. The loaded masks completely control the multi-resolution blending or multi-resolution fusing the output image.

In between these two steps the user may apply whatever transformation to the mask files, as long as their geometries and offsets remain the same. Thus the “Combine Images” box of Figure 3.1 becomes three activities as is depicted in Figure 3.2.

To further optimize this kind of workflow, both Enblend and Enfuse stop after mask generation if option --save-masks is given, but no output file is specified with the --output option. This way the time for pyramid generation, blending, fusing, and writing the final image to disk is saved, as well as no output image gets generated.

## 3.3  Interacting with Enblendc

This section explains how to find out about the inner workings of your version of Enblend without looking at the source code. And it states how to interact with Enblend besides passing command-line options and image filenames.

### 3.3.1  Finding Out Details About enblend

An enblend binary can come in several configurations. The exact name of the binary may vary and it may or may not reflect the “kind of enblend”. Therefore, enblend offers several options that allow the user to query exactly…

The information are explained in detail in the following sections.

#### Exact Version Number

Example 3.3.1 shows a possible output of ‘enblend --version’. The version number at the beginning of the text tells about the exact version of the binary. It is the number that can be compared with the version number of this document, which by the way is ⟨4.2⟩. Our slightly cranky markup (see also Notation) dispels copy-paste errors.

$enblend --version enblend 4.2-02c1f45857b4 Copyright (C) 2004-2009 Andrew Mihal. Copyright (C) 2009-2015 Christoph Spiel. License GPLv2+: GNU GPL version 2 or later <http://www.gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Written by Andrew Mihal, Christoph Spiel and others.  Example 3.3.1: Example output of enblend when called with option --version. The version indicator consist of a two (major and minor version) or three (major and minor version plus patch-level) numbers separated by dots and an optional hexadecimal identifier. Binaries from the “Development Branch” are assigned two-part version numbers, whereas a three-part version number is reserved for the “Stable Branch” of development. Officially released versions lack the hexadecimal identifier. Examples: 4.1.3-0a816672d475 Some unreleased version from the “Stable Branch”, which finally will lead to version 4.1.3. 4.1.3 Officially released version 4.1.3 in the “Stable Branch”. 4.2-1e4d237daabf Some unreleased version from the “Development Branch”, which finally will lead to version 4.2. 4.2 Officially released version 4.2 in the “Development Branch”. Matching the version codes is the only reliably way to pair a given binary with its manual page (“manual page for enblend 4.2-1e4d237daabf”) and its documentation. This document mentions the version code for example on its Title and the Abstract. The twelve-digit hexadecimal ID-CODE is automatically generated by our source-code versioning system, Mercurial. Use the ID-CODE to look up the version on the web in our public source code repository or, if you have cloned the project to your own workspace, with the command hg log --verbose --rev ID-CODE #### Compiled-In Features Adding option --verbose to --version will reproduce the information described in the previous section plus a list of “extra features”. Any unavailable feature in the particular binary queried returns Extra feature: …: no whereas available features answer “yes” followed by a detailed report on the feature and its connection to some library or specific hardware. Example 3.3.2 shows such a report. Remember that your binary may include more or less of the features displayed there.$ enblend --version --verbose
enblend 4.2-95f1fed2bf2d

Extra feature: dynamic linking support: yes
Extra feature: image cache: no
Extra feature: OpenMP: no

This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Andrew Mihal, Christoph Spiel and others.

 Example 3.3.2: Example output of enblend when called with options --version and --verbose together.

The ‘--version --verbose’ combo is one of the first things test if enblend “suddenly” behaves strangely.

1. “I’m running my enblend on a multi-core system, but it does not make use of it.”

Check for extra feature OpenMP.

2. “My enblend complains when I call it with ‘--gpu’!”

Check for extra feature OpenCL.

3. enblend is so slow!”

Ensure that neither feature mmap-view nor image-cache has been compiled in.

4. enblend eats away too much memory! Can I tell it to unload that onto the disk?”

No, there is no command-line switch for that, but you can use a version with mmap-view feature.

5. “My enblend has OpenMP enabled. Does it support dynamic adjustment of the number of threads?”

Under extra feature OpenMP look for “support for dynamic adjustment of the number of threads”.

#### Supported Images Formats

Enblend can read and write a fixed set of image formats if it was compiled to support them. For example the EXR-format requires special support libraries. Use option --show-image-formats to find out

• what image-data formats are supported,
• what filename extensions are recognized, and
• what per-channel depths have been compiled into the enblend binary.

The only three image formats always supported are

• JPEG,

• PNG, and

• TIFF.

All others are optional. In particular the high-dynamic range (HDR) format OpenEXR only gets compiled if several non-standard libraries are available.

The provided per-channel depths range from just one, namely “8 bits unsigned integral” (uint8) up to seven:

• 8 bits unsigned integral, ‘uint8
• 16 bits unsigned or signed integral, ‘uint16’ or ‘int16
• 32 bits unsigned or signed integral, ‘uint32’ or ‘int32
• 32 bits floating-point, ‘float
• 64 bits floating-point, ‘double

Table 3.1 summarizes the channel bit depths of some prominent image formats.

 Channel Bit-Depth Format Mask Profile Integral Floating-Point uint8 uint16 uint32 float double JPEG − • • − − − − PNG • • • • − − − PNM ? − • • • − − [V]TIFF • • • • • • •
 Table 3.1: Bit-depths of selected image formats. These are the maximum capabilities of the formats themselves, not Enblend’s. The “Mask”-column indicates whether the format supports an image mask (alpha-channel), see also Chapter 8. Column “Profile” shows whether the image format allows for ICC-profiles to be included; see also Chapter 7.

#### Name Of Builder

During building each enblend is automatically signed to give the users an extra level of confidence that it was constructed by someone that they can trust to get it right. Access this signature with ‘--show-signature’ and enblend will print something like

Compiled on sgctrl03 by Walter Harriman on Wed, Dec 22 2004, 16:07:22 GMT-7.

where machine name, person, and date-time depend on the build.

#### Compiler And Libraries Used To Build

Sometimes enblend refuses to start or runs into trouble because the libraries supplied to it do not match the ones it was compiled with. Option --show-software-components can be helpful to diagnose the problem in such cases, because it shows the version information of Enblend’s most important libraries as they have identified themselves during compile-time.

Furthermore the report reveals the compiler used to build enblend along with the most important compiler extensions like, for example, OpenMP. Example 3.3.3 shows such a report.

$enblend --show-software-components Compiler g++ 4.9.1 implementing OpenMP standard of 2013-7 implementing Cilk version 2.0 without support of "_Cilk_for" keyword Libraries GSL: 1.15 Little CMS: 2.7.0 Vigra: 1.10.0  Example 3.3.3: Output of enblend when asked to reveal the compiler that was used to build it along with the libraries it was linked against. ### 3.3.2 Console Messages Enblend is meant to read multiple images, “montage” them together, and finally write a single output image. So, any console messages either serve the entertainment desire of the user or indicate problems. When enblend is instructed to only show information about its configuration (see Section 4.2.6) the text goes to Standard Output. enblend sends error and warning messages to Standard Error. The messages follow a fixed format. enblend: [CATEGORY:] MESSAGE where CATEGORY is error: A serious problem that sooner or later will lead to a program stop. The result will definitely not be what the user wants – including no output image at all, as enblend deletes corrupted or incomplete output images. Most messages drop category name ‘error’ and plainly write MESSAGE: enblend: input image "1.tif" does not have an alpha channel If an ‘error’ actually leads to a premature termination of enblend, it returns code 1 to the operating system. On successful termination the return code is 0. warning: A problem that forces enblend to take an alternate execution path or drop some assumptions about the input. info: No problem, just a “nice-to-know” information for the user. note: Not a standalone CATEGORY, but an additional explanation that sometimes trails messages in one of the above categories. Errors, warnings and infos tell the causes, notes inform about the actions taken by enblend. Here is an example, where a warning gets augmented by a note: enblend: warning: input images too small for coarse mask enblend: note: switching to fine mask timing: A measurement of the execution duration and thus a sub-category of info. Sadly, not all messages can be sorted in the category scheme. Debug Messages: Though debug messages generally come devoid of a specific form the more civilized of them start each line with a plus sign ‘+’. Example: + checkpoint: leaving channel width alone Foreign Sources: enblend depends on various foreign software components that issue their own messages. We try to catch them and press them in our category scheme, but some of them invariably slip through. The most prominent members of this rogue fraction are the notices of VIGRA as e.g. enfuse: an exception occurred enfuse: Precondition violation! and LibTIFF: TIFFReadDirectory: Warning, img0001.tif: wrong data type 1 for "RichTIFFIPTC"; tag ignored. “Should-Never-Happen”: An internal consistency check fails or a cautious routine detects a problem with its parameters and racks up the digital equivalent of a nervous breakdown. Sometimes these messages end in the word ‘Aborted’. terminate called after throwing an instance of ’…’ what(): … Aborted If the installation of enblend is correct, this type of message may warrant a bug report as explained in Appendix B. In very unfortunate circumstances Enblend quits because of a problem, but does not show any message. The output file then either does not exist or it is broken. One known reason are out-of-memory situations, where the process needs additional memory, but cannot allocate it and while terminating needs even more memory so that the operating system wipes it out completely wherever it then happens to be in its execution path. ### 3.3.3 Environment Variables A small set of environment variables influences the execution of enblend. All of them depend on enblend having been compiled with certain features. The hint “(direct)” indicates genuine variables in enblend, whereas “(implicit)” denotes variables that control libraries that are linked with enblend. CILK_NWORKERS (implicit) Cilk-enabled versions only. This environment variable works for CilkPlus as OMP_NUM_THREADS (see below) does for OpenMP. It can be helpful for load balancing. OMP_DYNAMIC (implicit) OpenMP-enabled versions only. Control whether the OpenMP sub-system should parallelize nested parallel regions. This environment variable will only have an effect is the OpenMP sub-system is capable of dynamic adjustment of the number of threads (see explanations in Section 3.3.1). The important hot spots in the source code override the value of OMP_DYNAMIC. OMP_NUM_THREADS (implicit) OpenMP-enabled versions only. Control – which typically means: reduce – the number of threads under supervision of the OpenMP sub-system. By default enblend uses as many OpenMP-threads as there are CPUs. Use this variable for example to free some CPUs for other processes than enblend. TMPDIR (direct) mmap_view’-branch only. TMPDIR determines the directory and thus the drive where enblend stores all intermediate images. The best choice follows the same rules as for a swap-drive: prefer the fastest disk with the least load. # Chapter 4 Invocation Assemble the sequence of images INPUT… into a single IMAGE. enblend [OPTIONS] [--output=IMAGE] INPUT INPUT images are either specified literally or via so-called response files (see Section 4.4). The latter are an alternative to specifying image filenames on the command line. If omitted, the name of the output IMAGE defaults to ⟨a.tif⟩. ## 4.1 Input Image Requirements All input images for Enblend must comply with the following requirements. • Parts of the images overlap. • Each image has an alpha channel also called “mask”. • The images agree on their number of channels: • one plus alpha or • three plus alpha. This is, either all images are black-and-white (one channel and alpha channel) or all are RGB-color images (three channels and alpha channel). • The images agree on their number of bits-per-channel, i.e., their “depth”: • uint8, • uint16, • float, • etc. See option --depth for an explanation of different output depths. • Enblend understands the images’ filename extensions as well as their file formats. You can check the supported extensions and formats by calling Enblend with option --show-image-formats. Moreover, there are some good practices, which are not enforced by the application, but almost certainly deliver superior results. • Either all files lack an ICC profile, or all images are supplied with the same ICC profile. • If the images’ meta-data contains resolution information (“DPI”), it is the same for all pictures. ## 4.2 Command-Line Options In this section we group the options as the command-line help$ enblend --help

does and sort them alphabetically within their groups. For an alphabetic list of all options consult the Option Index.

enblend accepts arguments to any option in uppercase as well as in lowercase letters. For example, ‘deflate’, ‘Deflate’ and ‘DEFLATE’ as arguments to the --compression option described below all instruct enblend to use the Deflate compression scheme. This manual denotes all arguments in lowercase for consistency.

### 4.2.1  Common Optionsc

Common options control some overall features of Enblend. They are called “common” because they are used most often. However, in fact, Enblend and Enfuse do have these options in common.

--compression=COMPRESSION
Write a compressed output file. The default is not to compress the output image.

Depending on the output file format, Enblend accepts different values for COMPRESSION.

JPEG format.
The compression either is a literal integer or a keyword-option combination.
LEVEL
Set JPEG quality LEVEL, where LEVEL is an integer that ranges from 0–100.
jpeg[:LEVEL]
Same as above; without the optional argument just switch on standard JPEG compression.

jpeg-arith[:LEVEL]
Switch on arithmetic JPEG compression. With optional argument set the arithmetic compression LEVEL, where LEVEL is an integer that ranges from 0–100.
TIF format.
Here, COMPRESSION is one of the keywords:
none
Do not compress. This is the default.

deflate
Use the Deflate compression scheme also called ZIP-in-TIFF. Deflate is a lossless data compression algorithm that uses a combination of the LZ77 algorithm and Huffman coding.

jpeg[:LEVEL]
Use JPEG compression. With optional argument set the compression LEVEL, where LEVEL is an integer that ranges from 0–100.

lzw
Use Lempel-Ziv-Welch (LZW) adaptive compression scheme. LZW compression is lossless.

packbits
Use PackBits compression scheme. PackBits is a particular variant of run-length compression; it is lossless.
Any other format.
Other formats do not accept a COMPRESSION setting. However, the underlying VIGRA library automatically compresses png-files with the Deflate method. (VIGRA is the image manipulation library upon which Enblend is based.)

-l LEVELS
--levels=LEVELS
Use at most this many LEVELS for pyramid1 blending if LEVELS is positive, or reduce the maximum number of levels used by −LEVELS if LEVELS is negative; ‘auto’ or ‘automatic’ restore the default, which is to use the maximum possible number of levels for each overlapping region.

The number of levels used in a pyramid controls the balance between local and global image features (contrast, saturation, …) in the blended region. Fewer levels emphasize local features and suppress global ones. The more levels a pyramid has, the more global features will be taken into account.

As a guideline, remember that each new level works on a linear scale twice as large as the previous one. So, the zeroth layer, the original image, obviously defines the image at single-pixel scale, the first level works at two-pixel scale, and generally, the nth level contains image data at 2n-pixel scale. This is the reason why an image of width × height pixels cannot be deconstructed into a pyramid of more than
 ⌊ log2(min(width, height)) ⌋  levels.

If too few levels are used, “halos” around regions of strong local feature variation can show up. On the other hand, if too many levels are used, the image might contain too much global features. Usually, the latter is not a problem, but is highly desired. This is the reason, why the default is to use as many levels as is possible given the size of the overlap regions. Enblend may still use a smaller number of levels if the geometry of the overlap region demands.

Positive values of LEVELS limit the maximum number of pyramid levels. Depending on the size and geometry of the overlap regions this may or may not influence any pyramid. Negative values of LEVELS reduce the number of pyramid levels below the maximum no matter what the actual maximum is and thus always influence all pyramids. Use ‘auto’ or ‘automatic’ as LEVELS to restore the automatic calculation of the maximum number of levels.

The valid range of the absolute value of LEVELS is ⟨1⟩ to ⟨29⟩.

-o FILE
--output=FILE
Place blended output image in FILE. If ‘--output’ is omitted, Enblend writes the resulting image to ⟨a.tif⟩.

-v [LEVEL]
--verbose
[=LEVEL]
Without an argument, increase the verbosity of progress reporting. Giving more --verbose options will make Enblend more verbose; see Section 3.3.1 for an exemplary output. Directly set a verbosity level with a non-negative integral LEVEL. Table 4.1 shows the messages available at a particular LEVEL.

 Level Messages 0 only warnings and errors 1 reading and writing of images 2 mask generation, pyramid, and blending 3 reading of response files, color conversions 4 image sizes, bounding boxes and intersection sizes 5 Enblend only. detailed information on the optimizer runs 6 estimations of required memory in selected processing steps
 Table 4.1: Verbosity levels of enblend; each level includes all messages of the lower levels.

The default verbosity level of Enblend is ⟨1⟩.

Advanced options control e.g. the channel depth, color model, and the cropping of the output image.

--blend-colorspace=COLORSPACE
Force blending in selected COLORSPACE. Given well matched images this option should not change the output image much. However, if Enblend must blend vastly different colors (as e.g. anti-colors) the resulting image heavily depends on the COLORSPACE.

Usually, Enblend chooses defaults depending on the input images:

• For grayscale or color input images with ICC profiles the default is to use CIELUV colorspace.

• Images without color profiles and floating-point images are blended in the trivial luminance interval (grayscale) or RGB-color cube by default.

On the order of fast to slow computation, Enblend supports the following blend colorspaces.

identity
id
unit
Compute blended colors in a naïve way sidestepping any dedicated colorspace.
• Use trivial, 1-dimensional luminance interval (see Eqn. 7.1) for grayscale images and

• for color images utilize 3-dimensional RGB-cube (see Eqn. 7.6) spanned by the input ICC profile or sRGB if no profiles are present. In the latter case, consider passing option --fallback-profile to force a different profile than sRGB upon all input images.

lab
cielab
lstar
l-star
Blend pixels in the CIEL*a*b* colorspace.

luv
cieluv
Blend pixels in the CIEL*u*v* colorspace.

ciecam
ciecam02
jch
Blend pixels in the CIECAM02 colorspace.

Enblend only.
Please keep in mind that by using different blend colorspaces, blending may not only change the colors of the output image, but Enblend may choose different seam line routes as some seam-line optimizers are guided by image differences, which are different when viewed in different colorspaces.

-c
--ciecam
Deprecated. Use ‘--blend-colorspace=ciecam’ instead. To emulate the negated option --no-ciecam use --blend-colorspace=identity.

-d DEPTH
--depth=DEPTH
Force the number of bits per channel and the numeric format of the output image, this is, the DEPTH. The number of bits per channel is also known as “channel width” or “channel depth”.

Enblend always uses a smart way to change the channel depth to assure highest image quality at the expense of memory, whether requantization is implicit because of the output format or explicit through option --depth.

• If the output-channel depth is larger than the input-channel depth of the input images, the input images’ channels are widened to the output channel depth immediately after loading, that is, as soon as possible. Enblend then performs all blending operations at the output-channel depth, thereby preserving minute color details which can appear in the blending areas.
• If the output-channel depth is smaller than the input-channel depth of the input images, the output image’s channels are narrowed only right before it is written to the output FILE, that is, as late as possible. Thus the data benefits from the wider input channels for the longest time.

All DEPTH specifications are valid in lowercase as well as uppercase letters. For integer format, use

8
uint8
Unsigned 8 bit; range: 0…255
int16
Signed 16 bit; range: −32768…32767
16
uint16
Unsigned 16 bit; range: 0…65535
int32
Signed 32 bit; range: −2147483648…2147483647
32
uint32
Unsigned 32 bit; range: 0…4294967295

For floating-point format, use

r32
real32
float
IEEE754 single precision floating-point, 32 bit wide, 24 bit significant;
• Minimum normalized value: 1.2· 10−38
• Epsilon: 1.2· 10−7
• Maximum finite value: 3.4· 1038

r64
real64
double
IEEE754 double precision floating-point, 64 bit wide, 53 bit significant;
• Minimum normalized value: 2.2· 10−308
• Epsilon: 2.2· 10−16
• Maximum finite value: 1.8· 10308

If the requested DEPTH is not supported by the output file format, Enblend warns and chooses the DEPTH that matches best.

Versions with OpenEXR read/write support only.
The OpenEXR data format is treated as IEEE754 float internally. Externally, on disk, OpenEXR data is represented by “half” precision floating-point numbers.

OpenEXR half precision floating-point, 16 bit wide, 10 bit significant;

• Minimum normalized value: 9.3· 10−10
• Epsilon: 2.0· 10−3
• Maximum finite value: 4.3· 109

-f WIDTHxHEIGHT[+xXOFFSET+yYOFFSET]
Ensure that the minimum “canvas” size of the output image is at least WIDTH×HEIGHT. Optionally specify the XOFFSET and YOFFSET of the canvas, too.

This option only is useful when the input images are cropped TIFF files, such as those produced by nona.

Note that option -f neither rescales the output image, nor shrinks the canvas size below the minimum size occupied by the union of all input images.

-g
Save alpha channel as “associated”. See the TIFF documentation for an explanation.

The Gimp before version 2.0 and CinePaint (see Appendix A) exhibit unusual behavior when loading images with unassociated alpha channels. Use option -g to work around this problem. With this flag Enblend will create the output image with the “associated alpha tag” set, even though the image is really unassociated alpha.

-w [MODE]
--wrap
[=MODE]
Blend around the boundaries of the panorama, or “wrap around”.

As this option significantly increases memory usage and computation time only use it, if the panorama will be

• consulted for any kind measurement, this is, all boundaries must match as accurately as possible, or
• printed out and the boundaries glued together, or

• fed into a virtual reality (VR) generator, which creates a seamless environment.

Otherwise, always avoid this option!

With this option Enblend treats the set of input images (panorama) of width w and height h as an infinite data structure, where each pixel P(x, y) of the input images represents the set of pixels SP(x, y).

Solid-state physicists will be reminded of the Born-von Kármán boundary condition.

MODE takes the following values:

none
open
This is a “no-op”; it has the same effect as not giving ‘--wrap’ at all. The set of input images is considered open at its boundaries.
horizontal
Wrap around horizontally:
 SP(x, y) = {P(x + m w, y): m ∈ Z}.

This is useful for 360 horizontal panoramas as it eliminates the left and right borders.

vertical
Wrap around vertically:
 SP(x, y) = {P(x, y + n h): n ∈ Z}.

This is useful for 360 vertical panoramas as it eliminates the top and bottom borders.

both
horizontal+vertical
vertical+horizontal
Wrap around both horizontally and vertically:
 SP(x, y) = {P(x + m w, y + n h): m, n ∈ Z}.

In this mode, both left and right borders, as well as top and bottom borders, are eliminated.

Specifying ‘--wrap’ without MODE selects horizontal wrapping.

These options control the generation and the usage of masks.

Use a scaled-down or “coarse” version of the input images to create the seam line. This option reduces the number of computations necessary to compute the seam line and the amount of memory necessary to do so. It is the default.

If omitted FACTOR defaults to ⟨8⟩, this means, option --coarse-mask shrinks the overlapping areas by a factor of ⟨8⟩×⟨8⟩. With FACTOR = 8 the total memory allocated during a run of Enblend shrinks approximately by 80% and the maximum amount of memory in use at a time is decreased to some 40% in comparison to a full-size (“fine”) mask.

Valid range: FACTOR = 1, 2, 3, …, where 1 reproduces --fine-mask.

Also see the negated option, --fine-mask and Table 4.2.

 Active Options --no-optimize --optimize --fine-mask Use NFT mask. Vectorize NFT mask, optimize vertices with simulated annealing and Dijkstra’s shortest path algorithm, fill vector contours to recover mask. --coarse-mask Scale down overlap region, compute NFT mask and vectorize it, fill vector contours. Scale down overlap region, vectorize NFT mask, optimize vertices with simulated annealing and Dijkstra’s shortest path algorithm, fill vector contours to recover mask.
 Table 4.2: Various options that control the generation of masks. All mask computations are based on the Nearest-Feature Transformation (NFT) of the overlap region.

Instruct Enblend to employ the full-size images to create the seam line, which can be slow. Use this option, for example, if you have very narrow overlap regions.

Also see option --coarse-mask and Table 4.2.

See option --save-masks below for details.

--optimize
Use a multi-strategy approach to route the seam line around mismatches in the overlap region. This is the default. Table 4.3 explains these strategies; also see Table 4.2.

 Algorithm Tuning Parameters Simulated Annealing Tune with option --anneal = TAU : DELTA-E-MAX : DELTA-E-MIN : K-MAX. Simulated-Annealing. FIXExplain Simulated-Annealing!ME Dijkstra Shortest Path Tune with option --dijkstra = RADIUS. Dijkstra algorithm. FIXExplain Dijkstra algorithm!ME
 Table 4.3: Enblend’s strategies to optimize the seam lines between overlapping images.

Option --no-optimize negates --optimize and thus turns off seam line optimization. Combined with option --fine-mask this will produce the same type of mask as Enblend version 2.5, namely the result of a Nearest-Feature Transform (NFT).

Save the generated masks to IMAGE-TEMPLATE, which defaults to ‘⟨mask-%n.tif⟩’. Enblend saves masks as 8 bit grayscale, i.e. single channel images. For accuracy we recommend to choose a lossless format.

Use this option if you wish to edit the location of the seam line by hand. This will give you images of the right sizes that you can edit to make your changes. Later, use option --load-masks to blend the project with your custom seam lines.

Enblend will stop after saving all masks unless option --output is given, too. With both options given, this is, ‘--save-masks’ and ‘--output’, Enblend saves all masks and then proceeds to blend the output image.

IMAGE-TEMPLATE defines a template that is expanded for each input file. In a template a percent sign (‘%’) introduces a variable part. All other characters are copied literally. Lowercase letters refer to the name of the respective input file, whereas uppercase ones refer to the name of the output file (see Section 4.2.1). Table 4.4 lists all variables.

A fancy mask filename template could look like this:

It puts the mask files into the same directory as the output file ‘%D’, generates a two-digit index ‘%02n’ to keep the mask files nicely sorted, and decorates the mask filename with the name of the associated input file ‘%f’ for easy recognition.

--visualize[=VISUALIZE-TEMPLATE]
Create an image according to VISUALIZE-TEMPLATE that visualizes the un-optimized mask and the applied optimizations (if any). The default is ‘⟨vis-%n.tif⟩’.

This image will show Enblend’s view of the overlap region and how it decided to route the seam line. If you are experiencing artifacts or unexpected output, it may be useful to include this visualization image in your bug report. For a detailed description of the image, consult Chapter 6.

VISUALIZE-TEMPLATE defines a template that is expanded for each input file. In a template, a percent sign (‘%’) introduces a variable part; all other characters are copied literally. Lowercase letters refer to the name of the respective input file, whereas uppercase ones refer to the name of the output file (see option --output). Table 4.4 lists all variables.

 Format Interpretation %% Produces a literal ‘%’-sign. %i Expands to the index of the mask file starting at zero. ‘%i’ allows for setting a pad character or a width specification: % PAD WIDTH i PAD is either ‘0’ or any punctuation character; the default pad character is ‘0’. WIDTH is an integer specifying the minimum width of the number. The default is the smallest width given the number of input images, this is 1 for 2–9 images, 2 for 10–99 images, 3 for 100–999 images, and so on.Examples: ‘%i’, ‘%02i’, or ‘%_4i’. %n Expands to the number of the mask file starting at one. Otherwise it behaves identically to ‘%i’, including pad character and width specification. %p This is the full name (path, filename, and extension) of the input file associated with the mask.Example: If the input file is called /home/luser/snap/img.jpg, ‘%p’ expands to /home/luser/snap/img.jpg, or shorter: ‘%p’ ↦ /home/luser/snap/img.jpg. %P This is the full name of the output file. %d Is replaced with the directory part of the associated input file.Example (cont.): ‘%d’ ↦ /home/luser/snap. %D Is replaced with the directory part of the output file. %b Is replaced with the non-directory part (often called “basename”) of the associated input file.Example (cont.): ‘%b’ ↦ img.jpg. %B Is replaced with the non-directory part of the output file. %f Is replaced with the filename without path and extension of the associated input file.Example (cont.): ‘%f’ ↦ img. %F Is replaced with the filename without path and extension of the output file. %e Is replaced with the extension (including the leading dot) of the associated input file.Example (cont.): ‘%e’ ↦ .jpg. %E Is replaced with the extension of the output file.
 Table 4.4: Special format characters to control the generation of mask filenames. Uppercase letters refer to the output filename and lowercase ones to the input files.

### 4.2.4  Expert Options

Control inner workings of Enblend and in particular the interpretation of images.

--fallback-profile=PROFILE-FILENAME
Use the ICC profile in PROFILE-FILENAME instead of the default sRGB. This option only is effective if the input images come without color profiles and blending is not performed in the trivial luminance interval or RGB-cube.

Compare option --blend-colorspace and Chapter 7.3 on color profiles.

--layer-selector=ALGORITHM
Override the standard layer selector algorithm ‘⟨all-layers⟩’.

Enblend offers the following algorithms:

all-layers
Select all layers in all images.

first-layer
Select only first layer in each multi-layer image. For single-layer images this is the same as ‘all-layers’.

last-layer
Select only last layer in each multi-layer image. For single-layer images this is the same as ‘all-layers’.

largest-layer
Select largest layer in each multi-layer image, where the “largeness”, this is the size is defined by the product of the layer width and its height. The channel width of the layer is ignored. For single-layer images this is the same as ‘all-layers’.

no-layer
Do not select any layer in any image.

This algorithm is useful to temporarily exclude some images in response files.

--parameter=KEY[=VALUE][:…]
Set a KEY-VALUE pair, where VALUE is optional. This option is cumulative. Separate multiple pairs with the usual numeric delimiters.

This option has the negated form --no-parameter’, which takes one or more KEYs and removes them from the list of defined parameters. The special key ‘*’ deletes all parameters at once.

Parameters allow the developers to change the internal workings of Enblend without the need to recompile or relink.

Daniel Jackson: I just hope we won’t regret giving them those gate addresses.

Jack O’Neill: I don’t think we will, first one being a black hole and all. They get progressively darker after that.

-a
--pre-assemble
Pre-assemble non-overlapping images before each blending iteration.

This overrides the default behavior which is to blend the images sequentially in the order given on the command line. Enblend will use fewer blending iterations, but it will do more work in each iteration.

This option has the negated form --no-pre-assemble’, which restores the default.

-x
Checkpoint partial results to the output file after each blending step.

### 4.2.5  Expert Mask Generation Options

These options allow for a detailed control of the seam-line optimizers which govern the mask generation.

--anneal=TAU[:DELTA-E-MAX[:DELTA-E-MIN[:K-MAX]]]
Set the parameters of the Simulated Annealing optimizer. See Table 4.3.
TAU
TAU is the temperature reduction factor in the Simulated Annealing; it also can be thought of as “cooling factor”. The closer TAU is to one, the more accurate the annealing run will be, and the longer it will take.

Append a percent sign (‘%’) to specify TAU as a percentage.

Valid range: ⟨0⟩ < TAU < ⟨1⟩.

The default is ⟨0.75⟩; values around 0.95 are reasonable. Usually, slower cooling results in more converged points.

DELTA-E-MAX, DELTA-E-MIN
DELTA-E-MAX and DELTA-E-MIN are the maximum and minimum cost change possible by any single annealing move.

Valid range: ⟨0⟩ < DELTA-E-MIN < DELTA-E-MAX.

In particular they determine the initial and final annealing temperatures according to:

Tinitial
 DELTA-E-MAX log(K-MAX / (K-MAX − 2))

Tfinal
 DELTA-E-MIN log(K-MAX2 − K-MAX − 1)

The defaults are: DELTA-E-MAX: ⟨7000.0⟩ and DELTA-E-MIN: ⟨5.0⟩.

K-MAX
K-MAX is the maximum number of “moves” the optimizer will make for each line segment. Higher values more accurately sample the state space, at the expense of a higher computation cost.

Valid range: K-MAX ≥ ⟨3⟩.

The default is ⟨32⟩. Values around 100 seem reasonable.

Set the search RADIUS of the Dijkstra Shortest Path algorithm used in Dijkstra Optimization (see Table 4.3).

A small value prefers straight line segments and thus shorter seam lines. Larger values instruct the optimizer to let the seam line take more detours when searching for the best seam line.

Default: ⟨25⟩ pixels.

--image-difference=ALGORITHM[:LUMINANCE-WEIGHT[: CHROMINANCE-WEIGHT]]

Enblend calculates the difference of a pair of overlapping color images when it generates the primary seam with a Graph-Cut and also before it optimizes the seams. It employs a user-selectable ALGORITHM that is controlled by the

• weights for luminance differences, LUMINANCE-WEIGHT, wluma and

• color differences, CHROMINANCE-WEIGHT, wchroma.

For black-and-white images the difference is simple the absolute difference of each pair of pixels.

maximum-hue-luminance
maximum-hue-lum
max-hue-luminance
max-hue-lum
max
Calculate the difference d as the maximum of the differences of the luminances l and hues h of each pair of pixels P1 and P2:
 d  = max ⎛ ⎝ wluma × |l(P1) − l(P2)|, wchroma × |h(P1) − h(P2)| ⎞ ⎠ .

This algorithm was the default for Enblend up to version 4.0.

delta-e
de
Calculate the difference d as the Euclidean distance of the pixels in L*a*b* space:

 d = ⎡ ⎢ ⎣
 wluma × ⎛ ⎝ L(P1) − L(P2) ⎞ ⎠ 2 +

 wchroma × ⎛ ⎝ a(P1) − a(P2) ⎞ ⎠ 2 +

wchroma ×
b(P1) − b(P2)
2

 1/2

This is the default in Enblend version 4.1 and later.

Note that the “delta-E” mentioned here has nothing to do with DELTA-E-MAX and DELTA-E-MIN of option --anneal.

Both LUMINANCE-WEIGHT and CHROMINANCE-WEIGHT are non-negative. Enblend automatically normalizes the sum of LUMINANCE-WEIGHT and CHROMINANCE-WEIGHT to one. Thus,

--image-difference=delta-e:2:1

and

--image-difference=delta-e:0.6667:0.3333

define the same weighting function.

The default LUMINANCE-WEIGHT is ⟨1.0⟩ and the default CHROMINANCE-WEIGHT is ⟨1.0⟩.

At higher verbosity levels Enblend computes the true size of the overlap area in pixels and it calculates the average and standard deviation of the difference per pixel in the normalized luminance interval (0…1). These statistical measures are based on ALGORITHM, therefore they should only be compared for identical ALGORITHMs. The average difference is a rough measure of quality with lower values meaning better matches.

Set the mask vectorization DISTANCE that Enblend uses to partition each seam. Thus, break down the seam to segments of length DISTANCE each.

If Enblend uses a coarse mask (--coarse-mask) or Enblend optimizes (--optimize) a mask it vectorizes the initial seam line before performing further operations. See Table 4.2 for the precise conditions. DISTANCE tells Enblend how long to make each of the line segments called vectors here.

The unit of DISTANCE is pixels unless it is a percentage as explained in the next paragraph. In fine masks one mask pixel corresponds to one pixel in the input image, whereas in coarse masks one pixel represents for example ⟨8⟩ pixels in the input image.

Append a percentage sign (‘%’) to DISTANCE to specify the segment length as a fraction of the diagonal of the rectangle including the overlap region. Relative measures do not depend on coarse or fine masks, they are recomputed for each mask. Values around 5%–10% are good starting points.

This option strongly influences the mask generation process! Large DISTANCE values lead to shorter, straighter, less wiggly, less baroque seams that are on the other hand less optimal, because they run through regions of larger image mismatch instead of avoiding them. Small DISTANCE values give the optimizers more possibilities to run the seam around high mismatch areas.

What should never happen though, are loops or cusps in the seam line. Counter loops and cusps with higher weights of DISTANCE-WEIGHT (option --optimizer-weights), larger vectorization DISTANCEs, and TAUs (option --anneal) that are closer to one. Use option --visualize to check the results.

Valid range: DISTANCE ≥ ⟨4⟩.

Enblend limits DISTANCE so that it never gets below ⟨4⟩ even if it has been given as a percentage. The user will be warned in such cases.

Defaults: ⟨4⟩ pixels for coarse masks and ⟨20⟩ pixels for fine masks.

--optimizer-weights=DISTANCE-WEIGHT[:MISMATCH-WEIGHT]
Set the weights of the seam-line optimizer. If omitted, MISMATCH-WEIGHT defaults to 1.

The seam-line optimizer considers two qualities of the seam line:

• The distance of the seam line from its initial position, which has been determined by NFT (see option --no-optimize).
• The total “mismatch” accumulated along it.

DISTANCE-WEIGHT and MISMATCH-WEIGHT define how to weight these two criteria. Enblend up to version 3.2 used 1:1. This version of Enblend uses ⟨8.0⟩:⟨1.0⟩.

A large DISTANCE-WEIGHT pulls the optimized seam line closer to the initial position. A large MISMATCH-WEIGHT makes the seam line go on detours to find a path along which the mismatch between the images is small. If the optimized seam line shows cusps or loops (see option --visualize), reduce MISMATCH-WEIGHT or increase DISTANCE-WEIGHT.

Both weights must be non-negative. They cannot be both zero at the same time. Otherwise, their absolute values are not important as Enblend normalizes their sum.

--primary-seam-generator=ALGORITHM
Select the algorithm responsible for generating the general seam route.

This is the ALGORITHM that produces an initial seam line, which serves as the basis for later, optional optimizations. Nearest Feature Transform (NFT) is the only algorithm up to and including Enblend version 4.0. Version 4.1 added a Graph-Cut (GC) algorithm, which is the default for version 4.2 and later.

Valid ALGORITHM names are:

nearest-feature-transform
nft
Nearest Feature Transform

graph-cut
gc
Graph-Cut

See Chapter 5 for details on Enblend’s primary seam generators.

### 4.2.6  Information Optionsc

-h
--help
Print information on the command-line syntax and all available options, giving a boiled-down version of this manual.

--show-globbing-algorithms
Show all globbing algorithms.

Depending on the build-time configuration and the operating system the binary may support different globbing algorithms. See Section 4.4.3.

--show-image-formats
Show all recognized image formats, their filename extensions and the supported per-channel depths.

Depending on the build-time configuration and the operating system, the binary supports different image formats, typically: BMP, EXR, GIF, HDR, JPEG, PNG, PNM, SUN, TIFF, and VIFF and recognizes different image-filename extensions, again typically: bmp, exr, gif, hdr, jpeg, jpg, pbm, pgm, png, pnm, ppm, ras, tif, tiff, and xv.

The maximum number of different per-channel depths any enblend provides is seven:

• 8 bits unsigned integral, ‘uint8
• 16 bits unsigned or signed integral, ‘uint16’ or ‘int16
• 32 bits unsigned or signed integral, ‘uint32’ or ‘int32
• 32 bits floating-point, ‘float
• 64 bits floating-point, ‘double

--show-signature
Show the user name of the person who compiled the binary, when the binary was compiled, and on which machine this was done.

This information can be helpful to ensure the binary was created by a trustworthy builder.

--show-software-components
Show the name and version of the compiler that built Enblend followed by the versions of all important libraries against which Enblend was compiled and linked.

Technically, the version information is taken from header files, thus it is independent of the dynamic-library environment the binary runs within. The library versions printed here can help to reveal version mismatches with respect to the actual dynamic libraries available to the binary.

-V
--version
Output information on the binary’s version.

Team this option with --verbose to show configuration details, like the extra features that may have been compiled in. For details consult Section 3.3.1.

### 4.2.7  Program Flow And Option Settings

Figure 4.1 depicts Enblend’s internal work flow and shows what option influences which part. Enblend works incrementally. Thus, no matter whether starting with the first image or the result of blending any previous images, it loads the next image. After blending it the result again is a single image, which serves as base for the next input image, this is the next iteration.

Figure 4.1 somewhat simplifies the program flow.
• The Graph Cut algorithm needs an initial “guess” of the seam line. It gets it by running a Nearest-Feature Transform.
• If the overlap between the previous image and the next image is too small, the “Scale down mask” step is skipped and Enblend works with the mask in its original size (“fine mask”) no matter what the command-line options specify.

1
As Dr. Daniel Jackson correctly noted, actually, it is not a pyramid: “Ziggaurat, it’s a Ziggaurat.”

## 4.3  Option Delimitersc

Enblend and Enfuse allow the arguments supplied to the programs’ options to be separated by different separators. The online documentation and this manual, however, exclusively use the colon ‘:’ in every syntax definition and in all examples.

### 4.3.1  Numeric Arguments

Valid delimiters are the semicolon ‘;’, the colon ‘:’, and the slash ‘/’. All delimiters may be mixed within any option that takes numeric arguments.

Examples using some Enfuse options:

--contrast-edge-scale=0.667:6.67:3.5
Separate all arguments with colons.
--contrast-edge-scale=0.667;6.67;3.5
Use semi-colons.
--contrast-edge-scale=0.667;6.67/3.5
Mix semicolon and slash in weird ways.
--entropy-cutoff=3%/99%
All delimiters also work in conjunction with percentages.
--gray-projector=channel-mixer:3/6/1
Separate arguments with a colon and two slashes.
--gray-projector=channel-mixer/30;60:10
Go wild and Enfuse will understand.

### 4.3.2  Filename Arguments

Here, the accepted delimiters are comma ‘,’, semicolon ‘;’, and colon ‘:’. Again, all delimiters may be mixed within any option that has filename arguments.

Examples:

Separate all arguments with colons.
Use a comma.

## 4.4  Response Filesc

A response file contains names of images or other response filenames. Introduce response file names at the command line or in a response file with an ⟨@⟩ character.

Enblend and Enfuse process the list INPUT strictly from left to right, expanding response files in depth-first order. Multi-layer files are processed from first layer to the last. The following examples only show Enblend, but Enfuse works exactly the same.

Solely image filenames.
Example:
enblend image-1.tif image-2.tif image-3.tif

The ultimate order in which the images are processed is: image-1.tif, image-2.tif, image-3.tif.

Single response file.
Example:
enblend @ list

where file list contains

img1.exr
img2.exr
img3.exr
img4.exr

Ultimate order: img1.exr, img2.exr, img3.exr, img4.exr.

Mixed literal names and response files.
Example:
enblend @ master.list image-09.png image-10.png

where file master.list comprises of

image-01.png
@ first.list
image-04.png
@ second.list
image-08.png

first.list is

image-02.png
image-03.png

and second.list contains

image-05.png
image-06.png
image-07.png

Ultimate order: image-01.png, image-02.png, image-03.png, image-04.png, image-05.png, image-06.png, image-07.png, image-08.png, image-09.png, image-10.png,

### 4.4.1  Response File Format

Response files contain one filename per line. Blank lines or lines beginning with a ⟨#⟩ sign are ignored; the latter can serve as comments. Filenames that begin with a ⟨@⟩ character denote other response files. Table 4.5 states a formal grammar of response files in EBNF.

 response-file ::= line* line ::= (comment | file-spec) [‘\r’] ‘\n’ comment ::= space* ‘#’ text file-spec ::= space* ‘@ ’ filename space* space ::= ‘␣’ | ‘\t’

where text is an arbitrary string and filename is any filename.

 Table 4.5: EBNF definition of the grammar of response files.

In a response file relative filenames are used relative the response file itself, not relative to the current-working directory of the application.

The above grammar might surprise the user in the some ways.

White-space trimmed at both line ends
For convenience, white-space at the beginning and at the end of each line is ignored. However, this implies that response files cannot represent filenames that start or end with white-space, as there is no quoting syntax. Filenames with embedded white-space cause no problems, though.
Comments in response files always occupy a complete line. There are no “line-ending comments”. Thus, in
# exposure series
img-0.33ev.tif # "middle" EV
img-1.33ev.tif
img+0.67ev.tif

only the first line contains a comment, whereas the second line includes none. Rather, it refers to a file called

img-0.33ev.tif # "middle" EV
A ⟨@⟩ sign invariably introduces a response file, even if the filename’s extension hints towards an image.

If Enblend or Enfuse do not recognize a response file, they will skip the file and issue a warning. To force a file being recognized as a response file add one of the following syntactic comments to the first line of the file.

response-file: true
enblend-response-file: true

enfuse-response-file: true

Finally, Example 4.4.4 shows a complete response file.

# 4\pi panorama!

# These pictures were taken with the panorama head.
@ round-shots.list

# Freehand sky shot.
zenith.tif

# "Legs, will you go away?" images.
 Example 4.4.4: Example of a complete response file.

Comments that follow the format described in Table 4.6 are treated as instructions how to interpret the rest of the response file. A syntactic comment is effective immediately and its effect persists to the end of the response file, unless another syntactic comment undoes it.

 syntactic-comment ::= space* ‘#’ space* key space* ‘:’ space* value key ::= (‘A’…‘Z’ | ‘a’…‘z’ | ‘-’)+

where value is an arbitrary string.

 Table 4.6: EBNF definition of the grammar of syntactic comments in response files.

Unknown syntactic comments are silently ignored.

A special index for syntactic comments lists them in alphabetic order.

### 4.4.3  Globbing Algorithms

The three equivalent syntactic keys

• glob,
• globbing, or
• filename-globbing

control the algorithm that Enblend or Enfuse use to glob filenames in response files.

All versions of Enblend and Enfuse support at least two algorithms: literal, which is the default, and wildcard. See Table 4.7 for a list of all possible globbing algorithms. To find out about the algorithms in your version of Enblend or Enfuse use option --show-globbing-algorithms.

literal
Do not glob. Interpret all filenames in response files as literals. This is the default.

Please remember that white-space at both ends of a line in a response file always gets discarded.

wildcard
Glob using the wildcard characters ‘?’, ‘*’, ‘[’, and ‘]’.

The Win32 implementation only globs the filename part of a path, whereas all other implementations perform wildcard expansion in all path components. Also see glob(7).

none
Alias for literal.

shell
The shell globbing algorithm works as literal does. In addition, it interprets the wildcard characters ‘{’, ‘@’, and ‘~’. This makes the expansion process behave more like common UN*X shells.

sh
Alias for shell.
 Table 4.7: Globbing algorithms for the use in response files.

Example 4.4.5 gives an example of how to control filename-globbing in a response file.

# Horizontal panorama
# 15 images

# filename-globbing: wildcard

image_000[0-9].tif
image_001[0-4].tif
 Example 4.4.5: Control filename-globbing in a response file with a syntactic comment.

### 4.4.4  Default Layer Selection

The key layer-selector provides the same functionality as does the command-line option --layer-selector, but on a per response-file basis. See Section 4.2.1.

This syntactic comment affects the layer selection of all images listed after it including those in included response files until another layer-selector overrides it.

## 4.5  Layer Selectionc

Some image formats, like for example TIFF, allow for storing more than one image in a single file, where all the contained images can have different sizes, number of channels, resolutions, compression schemes, etc. The file there acts as a container for an ordered set of images.

In the TIFF-documentation these are known as “multi-page” files and because the image data in a TIFF-file is associated with a “directory”, the files sometimes are also called “multi-directory” files. In this manual, multiple images in a file are called “layers”.

The main advantage of multi-layer files over a set of single-layer ones is a cleaner work area with less image-files and thus an easier handling of the intermediate products which get created when generating a panorama or fused image, and in particularly with regard to panoramas of fused images.

The difficulty in working with layers is their lack of a possibly mnemonic naming scheme. They do not have telling names like taoth-vaclarush or valos-cor, but only numbers.

### 4.5.1  Layer Selection Syntax

To give the user the same flexibility in specifying and ordering images as with single-layer images, both Enblend and Enfuse offer a special syntax to select layers in multi-page files by appending a layer-specification to the image file name. Table 4.8 defines the grammar of layer-specifications.

Selecting a tuple of layers with a layer-specification overrides the active layer selection algorithm. See also option --layer-selector and Section 4.4. Layer selection works at the command-line as well as in Response Files; see Section 4.4.

 layer-specification ::= ‘[’ selection-tuple ‘]’ selection-tuple ::= selection [ ‘:’ selection ] selection ::= { singleton | range } range ::= [ ‘reverse’ ] [ range-bound ] ‘..’ [ range-bound ] range-bound ::= singleton | ‘_’ singleton ::= index | ‘-’ index

where index is an integral layer index starting at one.

 Table 4.8: EBNF definition of the grammar of layer specifications. In addition to the selection separator ‘:’ shown all usual numeric-option delimiters (‘⟨;:/⟩’) apply. The keyword for range reversal, ‘⟨reverse⟩’, can be abbreviated to any length and is treated case-insensitively.

The simplest layer-specification are the layer-indexes. The first layer gets index 1, the second layer 2, and so on. Zero never is a valid index! For convenience indexing backwards2 is also possible. This means by prefixing an index with a minus-sign (‘-’) counting will start with the last layer of the associated multi-page image, such that the last layer always has index -1, the next to last index -2 and so on. Out-of-range indexes are silently ignored whether forward or backward.

The single layer of a single-layer file always can be accessed either with index ‘1’ or ‘-1’.

Select a contiguous range of indexes with the range operator ‘⟨..⟩’, where the range-bounds are forward or backward indices. Leaving out a bound or substituting the open-range indicator ‘⟨_⟩’ means a maximal range into the respective direction.

Layer specifications ignore white space, but usual shells do not. This means that at the command-line

$enblend --output=out.tif --verbose multi-layer.tif[2:] works, whereas spaced-out out phrase ‘multi-layer.tif [2 : ]’ must be quoted$ enblend --output=out.tif --verbose ’multi-layer.tif[2 : ]’

Quoting will also be required if Enblend’s delimiters have special meanings to the shell.

Examples for an image with 8 layers.

[]
The empty selection selects nothing and in that way works like the layer-selector ‘no-layer’.
[2 : 4 : 5]
Select only layers 2, 4, and 5 in this order.
[2 : -4 : -3]
Like before, but with some backwards-counting indices.
[1 .. 4]
Layers 1 to 4, this is 1, 2, 3, and 4 in this order.
[_ .. 4]
Same as above in open-range notation.
[.. 4]
Same as above in abbreviated, open-range notation.
[-2 .. _]
The last two layers, which are 7 and 8 in our running example.
[_ .. _]
All layers in their natural order.
[..]
All layers in their natural order selected with the abbreviated notation.
[reverse _ .. _]
All layers in reverse order. This yields 8, 7, 6, 5, 4, 3, 2, and 1.
[rev ..]
All layers in reversed order as before selected with the abbreviated notation.
[r -3 ..]
The last three layers in reverse order, this is 8, 7 and 6 in our running example.
Shell expansion will not work anymore with a file name terminated by a layer specification expression (or anything else), because to the shell it is not a file name anymore. Work around with, for example,
$enblend ‘for x in image-??.tif; do echo$x[2]; done‘

or

$enblend$(ls -1 image-??.tif | sed -e ’s/$/[2]/’) The order of the indices determines the order of the layers, this is, the images. An index can occur multiple times, which causes layer to be considered again. Consequently, this will lead to an error with Enblend, but may be desired with Enfuse in soft-mask mode to give the image more weight by mentioning it more than once. ### 4.5.2 Tools for Multi-Page Files Here are some tools that are particularly useful when working with multi-page files. For more helpful utilities check out Appendix A. • Hugin’s stitcher, nona produces multi-page TIFF file, when called with the ‘-m TIFF_multilayer’-option. • The utility tiffcp of the TIFF-LibTIFF tool suite merges several TIFF-images into a single multi-page file. • The sister program tiffsplit splits a multi-page file into a set of single-page TIFF-images. • Another utility of the same origin, tiffinfo, is very helpful when inquiring the contents of single- or multi-page file TIFF-files. • All tools of the ImageMagick-suite, like, for example, convert and display use a similar syntax as Enblend to select layers (which in ImageMagick parlance are called “frames”) in multi-page files. Please note that ImageMagick tools start indexing at zero, whereas we start at one. • Enblend and Enfuse by default apply the ‘⟨all-layers⟩’ selector (see option --layer-selector) to each of the input images. Please bear in mind that some image-processing tools – none of the above though – do not handle multi-page files correctly, where the most unfruitful ones only take care of the first layer and silently ignore any further layers. 2 Samantha Carter: “There has to be a way to reverse the process. The answer has to be here.” # Chapter 5 Seam Generators This version of Enblend supports two main algorithms to generate seam lines. Use option --primary-seam-generator=ALGORITHM to select one of the generators. Nearest Feature Transform (NFT) ALGORITHM=nearest-feature-transform The Nearest Feature Transform1, also known as Distance Transform (DT), is a fast and efficient technique to produce a seam line route given the geometries of multiple overlapping images. NFT as implemented in this version of Enblend only takes into account the shape of the overlap area. It completely ignore the images’ contents. Graph-Cut (GC) ALGORITHM=graph-cut Graph-Cut is a region-oriented way of segmenting images. The generator is based on the idea of finding a minimum cost “cut” of a graph created from a given image pair. A “cut” is where the seam line appears. GC determines the cost from the overlapping images’ contents. The most significant difference between the two algorithms is the output mask gradation. NFT produces a coarse approximation of the seam, running as far away from the overlap-region borders as possible. The resulting mask could then be blended as-is, however, Enblend by default runs image-content dependent optimizers to increase the mask gradation and for example omits the regions where the images differ. The result is a finer seam line, which only loosely follows the shape of NFT’s primary seam. Graph-Cut, on the other hand, is capable of producing the final mask in one pass without the need of further optimizers. It looks for a seam line that is globally optimal, taking into account feature frequency, as well as image dissimilarity. This means, the seam is less likely to cross lines like for example fences, lampposts, or road markings, where they would be visible. The optimizers which run after NFT can also be run after GC. Nevertheless, GC works best just with a fine mask (option --fine-mask); optimizers are then automatically turned off to take full advantage of the detailed seam GC produces. GC requires more memory and computation time to complete than NFT. Thus, it is best to prefer NFT where the images used are large and execution time is crucial. If quality is the priority, using GC and fine mask usually produces visually more pleasing results. GC is currently limited to seams that begin and end on the images’ borders. This means that the algorithm cannot run in cases where, for example, one image is contained in another, resulting in a loop-like seam. In such cases, though, Enblend automatically falls back to a NFT-generated seam, making its application transparent to the user. 1 Muhammad H. Alsuwaiyel and Marina Gavrilova, “On the Distance Transform of Binary Images”, Proceedings of the International Conference on Imaging Science, Systems, and Technology, June 2000, Vols. I and II, pages 83–86. # Chapter 6 Visualization Image The visualization image shows the symmetric difference of the pixels in the rectangular region where two images overlap. The larger the difference the lighter shade of gray it appears in the visualization image. Enblend paints the non-overlapping parts of the image pair – these are the regions where no blending occurs – in ⟨dark red⟩. Table 6.1 shows the meanings of all the colors that are used in seam-line visualization images. ⟨dark red⟩ areas Non-overlapping parts of image pair. various shades of gray Difference of the pixel values in the overlap region. ⟨dark blue⟩ dot Location of an optimizer sample. ⟨medium green⟩ dot First sample of a line segment. ⟨light green⟩ dot Any other but first sample of a line segment. ⟨bright cyan⟩ dot State space sample inside the Dijkstra radius. ⟨bright magenta⟩ dot Non-converged point. ⟨dark yellow⟩ line Initial seam line as generated by the primary seam generator. ⟨bright yellow⟩ line Final seam line. ⟨bright white⟩ ⟨cross⟩ Non-movable, or “frozen” endpoint of a seam-line segment that no optimizer is allowed to move around. ⟨light orange⟩ ⟨diamond⟩ Movable endpoint of a seam-line segment, which seam-line optimizers can move.  Table 6.1: Colors and symbols used in seam-line visualization images. Figure 6.1 shows an example of a seam-line visualization. It was produced with an Enblend run at all defaults plus passing options --fine-mask and --visualize. The large ⟨dark red⟩ border is “off-limits” for Enblend, for the images do not overlap there. The dark wedge inside the ⟨dark red⟩ frame is where the images share a common region. The initial seam-line (⟨dark yellow⟩) is almost straight with the exception of a single bend on the left side of the image and the final seam-line (⟨bright yellow⟩) meanders around it. # Chapter 7 Color Spaces And Color Profilesc This chapter explains the connection of pixel data types, ICC-color profiles, blend color spaces in Enblend or Enfuse. Here, we collectively speak of blending and do not distinguish fusing, for the basic operations are the same. Furthermore, we assume the multi-resolution spline algorithm has calculated a set of weights wi for i = 1, 2, … and ∑wi = 1 for each pixel that must be blended from the participating input pixels Pi, i = 1, 2, …. In the simplest, non-trivial case we have to blend a pair of grayscale input pixels. Given their luminances L1, L2 and their weighting factor 0 ≤ w ≤ 1, what luminance L is their “weighted average”? This is the heart of Enblend’s and Enfuse’s pyramidal blending operations! We are in particular interested in a weighted average that appears visually correct, this is, our eyes and brains consider L convincing or at the very least credible. Note that Enblend and Enfuse face different obstacles in their respective domains of use. Enblend The overlapping areas usually are well matched both geometrically and photometrically. The differences of the pixels that must be blended are small. Enfuse (using a Soft Mask1) The input images greatly differ in exposure, saturation, or contrast. This is exactly why we want to fuse them. Thus, the luminance, saturation, and hue differences to be handled by Enfuse are generally quite high. The details of blending pixels and in particular color pixels is quite intricate, which is why we start this chapter with a mathematical introduction. ## 7.1 Mathematical Preliminaries Let us first address grayscale images because they only require us to talk about luminances. For a linear representation of luminances, we just blend for a given t with  L = t L1 + (1 − t) L2 with 0 ≤ t ≤ 1, (7.1) where the luminances Li, i = 1, 2, range from zero to their data-type dependent maximum value Lmax, thereby defining a “luminance interval”. We can always map this interval to (0, 1) by dividing the luminances by the maximum, which is why we call the latter “normalized luminance interval”:  (0, Lmax) → (0, 1) (7.2) Obviously,  0 ≤ L ≤ 1 (7.3) holds for all values L := L / Lmax in the normalized luminance interval. Sometimes images are gamma-encoded with exponent γ and the blended luminance becomes  L′ = ⎛ ⎝ t L11/γ + (1 − t) L21/γ ⎞ ⎠ γ, (7.4) which couples t and L′ in a non-linear way. See also Eric Brasseur’s explanation of the gamma error in picture scaling. Typical gamma values are γ = 2.2 for sRGB and AdobeRGB, 1.8 for AppleRGB, and ProPhotoRGB, 1.0 for Linear Rec709 RGB and any others with “linear” in their names. For an extensive overview check out Bruce Lindbloom’s Information on Working Color Spaces. The usual color-input images fed into Enblend are RGB-encoded, which means each pixel comes as a triple of values (r, g, b)T that represent the red, green, and blue parts. We apply the normalization (7.2) to each of the three primary colors and arrive at an RGB-cube” with unit edge length. The vectors of primary colors span the cube  → r =  1 0 0 ,  → g =  0 1 0 and  → b =  0 0 1 . For each point inside – familiarly called pixel – the generalization of (7.3) holds  0 0 0  r g b  1 1 1 . (7.5) Blending the pixels of color images is more complicated than blending plain luminances. Although we can write down the naïve blending equation, (7.1), again for RGB-coded pixels P1 :=  r1 g1 b1 and P2 :=  r2 g2 b2 and trivially arrive at P :=  r g b = t  r1 g1 b1 + (1 − t  r2 g2 b2 with 0 ≤ t ≤ 1, (7.6) but this means • we implicitly treat the color components ri, gi, bi as separate luminances, which they are not and moreover • we neglect the visual aspects, namely luminance, saturation, and hue of the blended color pixel P. ## 7.2 Floating-Point Images Floating-point images (EXR, floating-point TIFF, or VIFF) get a special treatment. Their values L are first converted by the Log-transform. Log(L) :=  1 + log(1 + L) for L ≥ 0 and 1 / (1 − L) otherwise, (7.7) which is undone by the inverse transform after blending. Here, log(x) with a lower-case initial denotes the natural logarithmic function (i.e. to base e). Figure 7.1 shows the forward transform in the range from −20 to 100. Around L = 0 function Log(L) has the series expansion Log(L) = 1 + L +  L2 2 + O(L3), for 0 ≤ L < 1. This transform serves two purposes: • During blending, even completely non-negative images can result in negative pixels. A Log-transform followed by the inverse guarantees all-positive output. • For HDR data, the Log-transform puts the samples closer to a perceptual space making the blending a little more pleasing. In the current version of Enblend and Enfuse it is strongly recommended to use blending inside the RGB-cube whenever the input data is in floating-point format; this is the default, too. ## 7.3 Color Profiles ICC-color profiles completely absorb gamma encodings (7.4) and ICC profile aware software like Enblend and Enfuse decode and encode images automatically respecting the gamma curves. Moreover color profiles define what is the darkest representable black, so called black-point  L = 0 and (r, g, b)T = (0, 0, 0)T and analogously what is the purest and brightest white, the white-point  L = 1 and (r, g, b)T = (1, 1, 1)T. By default, Enblend and Enfuse expect that either 1. no input image has a color profile or 2. all images come with the same ICC profile. Even black-and-white images benefit from having attached appropriate profiles! In Case 1. the applications blend grayscale images in the normalized luminance interval and color images inside the sRGB-cube. To override the default sRGB-profile select the desired profile with option --fallback-profile. In Case 2. the images first are by default transformed to CIELUV color space – respecting the input color profile – then they are blended or fused, and finally the data get transformed back to RGB color space defined by the profile of the input images. Consequently, the input profile is assigned to the output image. Enforce a different blending color space than CIELUV with option --blend-colorspace. Mixing different ICC profiles or alternating between images with profiles and without them generates warnings as it generally leads to unpredictable results. Floating-Point images are an exception to the above rules. They are always blended in the RGB cube by default. The next section describes their treatment in detail. ## 7.4 Blending Color Spaces Enblend and Enfuse offer to work inside the RGB-cube (7.5) or in several perceptually uniform color spaces. To override the default select a particular blending color space with option --blend-colorspace. Here are the four available color spaces. Identity Space / RGB-Color Cube Calculate the blended pixel inside the luminance interval (7.1) for grayscale images and inside the RGB-color cube as given in (7.6). This is the fastest color space to do computations within, i.e. it consumes by far the least computing power, because no transform to or from any of the perceptually uniform color spaces is done. L*a*b* Represent each pixel as lightness L*, red-green difference a*, and yellow-blue difference b*. The L*a*b* color space encompasses all perceivable colors. It is completely independent of any device characteristics, approximates human vision, and is perceptually uniform. Enblend uses perceptual rendering intent and either the input profile’s white-point or, if the ICC-profile lacks the cmsSigMediaWhitePointTag, fall back to the D50 white-point (see, e.g. Standard illuminant). The conversions from and to L*a*b* are moderately fast to compute; L*a*b* mode is two to three times slower than working within the RGB-color cube. CIEL*u*v* Represent each pixel as lightness L* and two color differences u* and v*. Formulas of each are too complicated to show them here. The L*u*v* tries to be perceptually uniform in lightness as well as in color. The applications use the same rendering intent and white-point as with L*a*b*. The conversions from and to L*u*v* are almost as fast to compute as L*a*b*. CIECAM02 Represent each pixel as lightness J, chroma C (“colorfulness”), and hue angle h. Internally, the polar coordinates (C, h) are translated to Cartesian coordinates for the pyramids. The transformations to CIECAM02 color space and back use perceptual rendering intent, the D50 white point (see, e.g. Standard illuminant), 500 lumen surrounding light (“average” in CIECAM02 parlance), and assume complete adaption. Both CIELUV and CIELAB only model the color information generated for small and isolated color samples. They cannot model the contextual effects of color perception. However, CIECAM02 can represent luminance adaptation, chromatic contrast and chromatic assimilation that arise in real world viewing conditions with heterogeneous, strongly contrasted, or three dimensional color sources. Computationally, CIECAM02 is the most expensive blend color space. If an appreciable number of pixels need additional refinement steps the speed of the transformation further drops. Expect CIECAM02 mode to be 8–800 times slower than blending within the RGB-color cube. Surprisingly often blending “inside the RGB-cube” works, although perceptually uniform color spaces, which represent luminance, saturation, and hue are preferable for blending and fusing operations. ## 7.5 Practical Considerations • For small projects stick with the default blend colorspaces. • For large projects switch on blending in the RGB color cube to speed up the assembly of the images. When satisfied with all other parameters use one of the computationally more expensive, but perceptually uniform color spaces. • Banding is best fought by input images with a high bit depth (≥ 16 bits per channel). A cheap and mostly vain trick is to force a large output bit depth with option --depth. No blend color space can avoid banding if parts of the input images are almost “monochrome”. • Enblend only. No color space can fix a seam-line gone haywire! First re-run Enblend with --visualize to inspect the seam-lines, then try one or more of the following 1 Fusing with a Hard Mask is different, because exactly one weight factor is unity and all the others are zero. There is nothing to blend – just to copy. # Chapter 8 Understanding Masksc A binary mask indicates for every pixel of an image if this pixel must be considered in further processing, or ignored. For a weight mask, the value of the mask determines how much the pixel contributes, zero again meaning “no contribution”. Masks arise in two places: as part of the input files and as separate files, showing the actual pixel weights prior to image blending or fusion. We shall explore both occurrences in the next sections. ## 8.1 Masks In Input Files Each of the input files for Enblend and Enfuse can contain its own mask. Both applications interpret them as binary masks no matter how many bits per image pixel they contain. Use ImageMagick’s identify (see Example 8.1.6) or, for TIFF files only, tiffinfo (see Example 8.1.7) to inquire quickly whether a file contains a mask. Appendix A shows where to find these programs on the web.$ identify -version
Version: ImageMagick 6.7.7-10 2014-03-08 Q16 http://www.imagemagick.org
Features: OpenMP

$identify -format "%f %m %wx%h %r %q-bit" image-0000.tif image-0000.tif TIFF 917x1187 DirectClass sRGB Matte 16-bit ^^^^^ mask  Example 8.1.6: Using identify to find out about the mask in image-0000.tif. ‘Matte’ indicates the existence of a mask.$ tiffinfo
LIBTIFF, Version 4.0.2
Copyright (c) 1991-1996 Silicon Graphics, Inc.

tiffinfo image-0000.tif TIFF Directory at off set 0x3a8182 (3834242) Subfile Type: (0 = 0x0) Image Width: 917 Image Length: 1187 Resolution: 150, 150 pixels/inch Position: 0, 0 Bits/Sample: 8 Sample Format: unsigned integer Compression Scheme: PackBits Photometric Interpretation: RGB color Extra Samples: 1<unassoc-alpha> mask Orientation: row 0 top, col 0 lhs Samples/Pixel: 4 R, G, B, and mask Rows/Strip: 285 Planar Configuration: single image plane ImageFullWidth: 3000 ImageFullLength: 1187  Example 8.1.7: Using tiffinfo to find out about the mask in image-0000.tif. Here the line ‘Extra Samples’ indicates one extra sample per pixel, which is interpreted as an unassociated alpha-channel; Enblend and Enfuse interpret this as mask. The second hint tiffinfo gives is in ‘Samples/Pixel’, where – for a RGB-image – the 4 = 3 + 1 tells about the extra channel. The “Matte” part of the image class and the “Extra Samples” line tell us that the file features a mask. Also, many interactive image manipulation programs show the mask as a separate channel, sometimes called “alpha”. There, the white (high mask value) parts of the mask enable pixels and black (low mask value) parts suppress them. The multitude of terms all describing the concept of a mask is confusing. Mask A mask defines a selection of pixels. A value of zero represents an unselected pixel. The maximum value (“white”) represents a selected pixel and the values between zero and the maximum are partially selected pixels. See Gimp-Savy. Alpha Channel The alpha channel stores the transparency value for each pixel, typically in the range from zero to one. A value of zero means the pixel is completely transparent, thus does not contribute to the image. A value of one on the other hand means the pixel is completely opaque. Matte The notion “matte” as used by ImageMagick refers to an inverted alpha channel, more precisely: 1 − alpha. See ImageMagick for further explanations. Enblend and Enfuse only consider pixels that have an associated mask value other than zero. If an input image does not have an alpha channel, Enblend warns and assumes a mask of all non-zero values, that is, it will use every pixel of the input image for fusion. Stitchers like nona add a mask to their output images. Sometimes it is helpful to manually modify a mask before fusion. For example to suppress unwanted objects (insects and cars come into mind) that moved across the scene during the exposures. If the masks of all input images are black at a certain position, the output image will have a hole in that position. ## 8.2 Weight Mask Files FIXShow some weight masks and explain them.ME You have your answer, Daniel Jackson. I suggest you act on it.Morgan le Fay (Ganos Lal) # Appendix A Helpful Programs And Librariesc Several programs and libraries have proven helpful when working with Enblend or Enfuse. ## A.1 Raw Image Conversion • Darktable is an open-source photography workflow application and raw-image developer. • DCRaw is a universal raw-converter written by David Coffin. • RawTherapee is powerful open-source raw converter for Win*, MacOS and Linux. • UFRaw is a raw-converter written by Udi Fuchs and based on DCRaw (see above). It adds a GUI (ufraw), versatile batch processing (ufraw-batch), and some additional features such as cropping, noise reduction with wavelets, and automatic lens-error correction. ## A.2 Image Alignment and Rendering • Hugin is a GUI that aligns and stitches images. It comes with several command-line tools, like for example nona to stitch panorama images, align_image_stack to align overlapping images for HDR or create focus stacks, and fulla to correct lens errors. • PanoTools the successor of Helmut Dersch’s original PanoTools offers a set of command-line driven applications to create panoramas. Most notable are PTOptimizer for control point optimization and PTmender, an image stitcher. ## A.3 Image Manipulation • CinePaint is a branch of an early Gimp forked off at version 1.0.4. It sports much less features than the current Gimp, but offers 8 bit, 16 bit and 32 bit color channels, HDR (for example floating-point TIFF, and OpenEXR), and a tightly integrated color management system. • The Gimp is a general purpose image manipulation program. At the time of this writing it is still limited to images with only 8 bits per channel. • G’Mic is an open and full-featured framework for image processing, providing several different user interfaces to convert, manipulate, filter, and visualize generic image datasets. • Both ImageMagick and GraphicsMagick are general-purpose command-line controlled image-manipulation programs, for example, convert, display, identify, and montage. GraphicsMagick bundles most ImageMagick invocations in the single dispatcher call to gm. ## A.4 High Dynamic Range • OpenEXR offers libraries and some programs to work with the EXR HDR-format, for example the EXR display utility exrdisplay. • PFSTools read, write, modify, and tonemap high-dynamic range (HDR) images. ## A.5 Major Libraries • LibJPEG is a library for handling the JPEG (JFIF) image format. • LibPNG is a library that handles the Portable Network Graphics (PNG) image format. • LibTIFF offers a library and utility programs to manipulate the ubiquitous Tagged Image File Format, TIFF. The nifty tiffinfo command in the LibTIFF distribution quickly inquires the most important properties of TIFF files. ## A.6 Meta-Data Handling • EXIFTool reads and writes EXIF meta-data. In particular it copies meta-data from one image to another. • LittleCMS is the color-management library used by Hugin, DCRaw, UFRaw, Enblend, and Enfuse. It supplies some binaries, too. tificc, an ICC color profile applier, is of particular interest. ## A.7 Camera Firmware Extension • Magic Lantern is a software add-on that runs from the SD (Secure Digital) or CF (Compact Flash) card and adds new features to cameras of a certain Japanese brand of cameras as for example • Dual-ISO (more precisely: simultaneous dual sensor speed); this operation mode may in fact obviate the need for Enfuse. • Focus stacking • HDR-bracketing # Appendix B Bug Reportsc Most of this appendix was taken from the Octave documentation. Bug reports play an important role in making Enblend and Enfuse reliable and enjoyable. When you encounter a problem, the first thing to do is to see if it is already known. To this end, visit the package’s LaunchPad bug ⟨database⟩. Search it for your particular problem. If it is not known, please report it. In order for a bug report to serve its purpose, you must include the information that makes it possible to fix the bug. ## B.1 Have You Really Found a Bug? If you are not sure whether you have found a bug, here are some guidelines: • If Enblend or Enfuse get a fatal signal, for any options or input images, that is a bug. • If Enblend or Enfuse produce incorrect results, for any input whatever, that is a bug. • If Enblend or Enfuse produce an error message for valid input, that is a bug. • If Enblend or Enfuse do not produce an error message for invalid input, that is a bug. ## B.2 How to Report Bugs The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it. Often people omit facts because they think they know what causes the problem and they conclude that some details do not matter. Play it safe and give a specific, complete example. Keep in mind that the purpose of a bug report is to enable someone to fix the bug if it is not known. Always write your bug reports on the assumption that the bug is not known. Try to make your bug report self-contained. If we have to ask you for more information, it is best if you include all the previous information in your response, as well as the information that was missing. To enable someone to investigate the bug, you should include all these things: • The exact version and configuration of Enblend. You can get the data by running enblend with the options --version and --verbose together. See also Section 3.3.1 on how to find out the exact configuration of your binary. • A complete set of input images that will reproduce the bug. Strive for a minimal set of small images, where images up to 1500×1000 pixels qualify as small. • The type of machine you are using, and the operating system name and its version number. • A complete list of any modifications you have made to the source. Be precise about these changes. Show a delta generated with diff for them. • Details of any other deviations from the standard procedure for installing Enblend and Enfuse. • The exact command line you use to call Enblend or Enfuse, which then triggers the bug. Examples: ~/local/bin/enblend -v \
--optimizer-weights=3:2 \
image-1.png image-2.png

or:

\$ /local/bin/enfuse \
--verbose \
--exposure-weight=0 --saturation-weight=0 --entropy-weight=1 \
--gray-projector=l-star \
--entropy-cutoff=1.667% \
layer-01.ppm layer-02.ppm layer-03.ppm

If you call Enblend or Enfuse from within a GUI like, for example, Hugin or ImageFuser by Harry van der Wolf, copy&paste or write down the command line that launches Enblend or Enfuse.

• A description of what behavior you observe that you believe is incorrect. For example, “The application gets a fatal signal,” or, “The output image contains black holes.”

Of course, if the bug is that the application gets a fatal signal, then one cannot miss it. But if the bug is incorrect output, we might not notice unless it is glaringly wrong.

## B.3  Sending Patches for Enblend or Enfuse

If you would like to write bug fixes or improvements for Enblend or Enfuse, that is very helpful. When you send your changes, please follow these guidelines to avoid causing extra work for us in studying the patches. If you do not follow these guidelines, your information might still be useful, but using it will take extra work.

• Send an explanation with your changes of what problem they fix or what improvement they bring about. For a bug fix, just include a copy of the bug report, and explain why the change fixes the bug.
• Always include a proper bug report for the problem you think you have fixed. We need to convince ourselves that the change is right before installing it. Even if it is right, we might have trouble judging it if we do not have a way to reproduce the problem.
• Include all the comments that are appropriate to help people reading the source in the future understand why this change was needed.
• Do not mix together changes made for different reasons. Send them individually.

If you make two changes for separate reasons, then we might not want to install them both. We might want to install just one.

• Use the version control system to make your diffs. Prefer the unified diff format: hg diff --unified 4.
• You can increase the probability that your patch gets applied by basing it on a recent revision of the sources.

# Appendix C  Authorsc

Andrew Mihal (acmihal@users.sourceforge.net) has written Enblend and Enfuse.

Contributors (in alphabetical order)

Thanks to Simon Andriot and Pablo Joubert for suggesting the Mertens-Kautz-Van Reeth technique and the name “Enfuse”.

# Appendix D  The GNU Free Documentation Licensec

Version 1.2, November 2002

51 Franklin St, Fifth Floor, Boston, MA 02110–1301, USA

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

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# Syntactic Comment Index

 enblend-response-file, 4.4.1 enfuse-response-file, 4.4.1 filename-globbing, 4.4.3 glob, 4.4.3 globbing, 4.4.3 layer-selector, 4.4.4 response-file, 4.4.1

# Program/Application Index

 CinePaint, A.3 Cinepaint, 4.2.2 Darktable, A.1 Gimp, 3.1, 4.2.2, A.3 GraphicsMagick, A.3 Hugin, 1, 3.1, 4.5.2, A.2, B.2 ImageFuser, B.2 ImageMagick, A.3 LittleCMS, A.6 Magic Lantern, A.7 Mercurial, 3.3.1 PanoTools, 1, 3.1, A.2 RawTherapee, A.1 UFRaw, A.1 align_image_stack (Hugin), A.2 convert (ImageMagick), 4.5.2, A.3 dcraw, 3.1, A.1 display (ImageMagick), 4.5.2 display (ImageMagick), A.3 exiftool, A.6 exrdisplay (OpenEXR), A.4 fulla (Hugin), A.2 gm (GraphicsMagick), A.3 gmic, A.3 identify (ImageMagick), 8.1, A.3 montage (ImageMagick), A.3 nona (Hugin), 4.2.2, 4.5.2, 8.1, A.2 PFSTools, A.4 PTmender (PanoTools), A.2 PTOptimizer (PanoTools), A.2 tiffcp (LibTIFF), 4.5.2 tiffinfo (libtiff), 8.1 tiffinfo (LibTIFF), 4.5.2 tiffinfo (libtiff), A.5 tiffsplit (LibTIFF), 4.5.2 tificc (LittleCMS), A.6 ufraw-batch, A.1 ufraw, 3.1, A.1

If a program belongs to a larger package, it has its association mentioned in parenthesis.

# Option Index

 --anneal, 4.2.5 --blend-colorspace, 4.2.2 --ciecam, 4.2.2 --coarse-mask, 4.2.3 --compression, 4.2.1 --depth, 4.2.2 --dijkstra, 4.2.5 --fallback-profile, 4.2.4 --fine-mask, 4.2.3 --help, 4.2.6 --image-difference, 4.2.5 --layer-selector, 4.2.4 --levels, 4.2.1 --load-masks, 3.2, 4.2.3 --mask-vectorize, 4.2.5 --no-ciecam, 4.2.2 --no-optimize, 4.2.3 --no-parameter, 4.2.4 --no-pre-assemble, 4.2.4 --optimize, 4.2.3 --optimizer-weights, 4.2.5 --output, 3.2, 4.2.1 --parameter, 4.2.4 --pre-assemble, 4.2.4 --primary-seam-generator, 4.2.5 --save-masks, 3.2, 4.2.3 --show-globbing-algorithms, 4.2.6 --show-image-formats, 3.3.1, 4.2.6 --show-signature, 3.3.1, 4.2.6 --show-software-components, 3.3.1, 4.2.6 --verbose, 3.3.1, 4.2.1 --version, 3.3.1, 3.3.1, 4.2.6 --visualize, 4.2.3 --wrap, 2, 4.2.2 -a (long: --pre-assemble), 4.2.4 -c (long: --ciecam), 4.2.2 -d (long: --depth), 4.2.2 -f, 4.2.2 -g, 4.2.2 -h (long: --help), 4.2.6 -l (long: --levels), 4.2.1 -o (long: --output), 4.2.1 -V (long: --version), 4.2.6 -v (long: --verbose), 4.2.1 -w (long: --wrap), 4.2.2 -x, 4.2.4