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Gifsicle changes

1.95 19.Feb.2024
Fix some bugs.

1.94 23.Jun.2023
Fix some bugs.

1.93 30.Jun.2021
Fix security bug on certain resize operations with ‘--resize-method=box’.

Fix problems with colormapless GIFs.

1.92 18.Apr.2019
Add ‘--lossy’ option from Kornel Lipiński.

Remove an assertion failure possible with ‘--conserve-memory’ + ‘--colors’ + ‘--careful’.

1.91 5.Jan.2018
Several security bug fixes with malicious GIFs.

1.90 14.Aug.2017
Kill a use-after-free error reported by @junxzm1990.

1.89 11.Jul.2017
Add SIMD support for resizing. When enabled this improves resize performance enormously for complex resize methods.

Add thread support for resizing. ‘-j[NTHREADS]’ tells gifsicle to use up to NTHREADS threads to resize an input image. There are several caveats---multiple threads can be only used on unoptimized images. Thanks to Github user @wilkesybear.

Quashed several crashes and undefined behaviors. Thanks to Github users including @pornel, @strazzere, and @b0b0505.

Minor bug fixes.

1.88 1.Jul.2015
Fix bug where long comments were read incorrectly. Reported by kazarny.

Add --no-ignore-errors option.

1.87 9.Dec.2014
Always optimize as if the background is transparent. This fixes some rare bugs reported by Lars Dieckow.

Fix --crop issue with must-be-preserved frames that are out of the crop window.

1.86 14.Oct.2014
Further fix --rotate + --crop.

1.85 14.Oct.2014
Greatly improve optimization time for images with many colors.

Add --no-extensions (with the s) and document those options more.

Fix bug in interaction of --resize and --rotate reported by Michał Ziemba.

1.84 29.Jun.2014
Correct optimizer bug that affected GIFs with 65535 or more total colors. Reported by Jernej Simončič.

1.83 21.Apr.2014
Correct bug in custom gamma values reported by Kornel Lesiński.

Update Windows build.

1.82 27.Mar.2014
Correct bug in ‘mix’ sampling method reported by Bryan Stillwell.

1.81 24.Mar.2014
Correct bug in ‘mix’ sampling method reported by Bryan Stillwell.

1.80 18.Mar.2014
Bug fixes and improved error messages.

1.79 17.Mar.2014
Major improvements in image scaling. Work sponsored by Tumblr via Mike Hurwitz.

Add new resize sampling methods ‘mix’, ‘box’, ‘catrom’, ‘mitchell’, ‘lanczos2’, and ‘lanczos3’, selectable by ‘--resize-method’. The ‘catrom’ filter often gives good results; the slightly faster ‘mix’ method (a bilinear interpolator) is now the default. These new sampling methods consider all of the image’s input colors when shrinking the image, producing better, less noisy output for most images.

Add ‘--resize-colors’, which allows Gifsicle to enlarge the palette when resizing images. This is particularly important when shrinking images with small colormaps---e.g., shrinking a black-and-white image should probably introduce shades of gray.

Support extensions such as XMP4 in which extension packet boundaries matter. Reported by ‘ata4’.

Many bug fixes, especially to cropping. Thanks to Tumblr and to Bryan Stillwell, Tal Lev-Ami, "Marco," and others.

1.78 9.Dec.2013
Correct an optimization bug introduced in 1.76. Reported by Tom Roostan.

1.77 26.Nov.2013
Major improvements to color selection (important when reducing colormap size). Use gamma-corrected colors in selection and dithering; this makes image quality much better. Also, when reducing colors with dithering, prefer to select colors that dithering can’t approximate.

Add ordered dithering modes, which avoid animation artifacts. The default ordered dithering mode (‘--dither=ordered’) is a novel mode that combines some of the visual advantages of error diffusion with the artifact avoidance of ordered dithering.

Add halftone dithering (‘--dither=halftone’).

gifview: Improved cache memory management for better animations. Collect memory for old frames based on an explicit --memory-limit (default 40MB).

gifview: Add ‘--fallback-delay’ option, to specify a fallback delay for frames with delay 0. Thanks to Sung Pae.

1.76 20.Nov.2013
Fix ‘-O2’ crashes introduced with ‘--resize’ improvements. Reported by Bryan Stillwell.

1.75 18.Nov.2013
Improve ‘--careful’ (fewer crashes). Reported by Bryan Stillwell.

Improve ‘-O2’: again, don’t refuse to optimize images with local color tables. Reported by Bryan Stillwell.

Greatly improve ‘--dither’ speed.

1.74 16.Nov.2013
Improve ‘--resize’ behavior: avoid animation artifacts due to different rounding decisions. Also speed it up. Reported by Bryan Stillwell.

1.73 15.Nov.2013
Fix bug where ‘-O2’ would refuse to optimize some images with local color tables, claiming that "more than 256 colors were required". What was really required is previous disposal. Reported by Bryan Stillwell.

1.72 9.Nov.2013
Fix crash bugs on some combinations of ‘--crop’ and ‘--resize’ (prevalent on images whose first frame didn’t cover the whole logical screen). Reported by Bryan Stillwell.

1.71 15.Jun.2013
Avoid rounding errors in ‘--resize’. Reported by Paul Kane.

Report error when ‘-I’ is combined with ‘-b’. Reported by Frank Dana.

Frame selections also apply in batch mode. Reported by LOU Yu Hong Leo.

1.70 31.Jan.2013
Fix ‘--crop’ bug introduced in version 1.68, visible in images containing local color tables. Bug reported by Alberto Nannini.

1.69 31.Jan.2013
Minor bug fix release.

1.68 24.Nov.2012
gifsicle: Alberto Nannini reported some images that are optimized beyond what Gifsicle can do. In fact, Gifsicle’s GIF writer was limited enough that even when running without optimization, it seriously expanded the input images. Some improvements to Gifsicle’s writing procedure avoid this problem; now ‘gifsicle IMAGE’ will produce large results less often, and when it does generate larger results, they’re larger by hundreds of bytes, not hundreds of thousands. However, due to restrictions in the current optimizer (and on my time), I was unable to improve ‘gifsicle -O3”s handling of these images. The optimizer that produced the images must be doing something pretty clever. (Is it SuperGIF?)

1.67 5.May.2012
gifsicle: Frame specifications like "#2-0" are allowed; they insert frames in reverse order. Feature request from Leon Arnott.

gifview: Add --min-delay option.

1.66 2.Apr.2012
gifsicle: Add -Okeep-empty for Gerald Johanson.

1.65 2.Apr.2012
gifsicle: Several users (Kornel Lesiński and others) reported "bugs" with Gifsicle-optimized images and Mac programs like Safari. The bug is in Safari, but add --careful to work around it.

Improve -O3 a bit (although for some images, the new -O3 is bigger than the old).

1.64 22.Nov.2011
gifsicle: Add --resize-fit options. Tom Glenne request.

1.63 17.Jul.2011
gifsicle: Avoid crash on frame selections where frames are repeated. Werner Lemberg report.

1.62 4.Apr.2011
gifsicle: -O3 optimization level tries even harder, so that now gifsicle -O3 should never produce larger results than gifsicle-1.60 -O2. Jernej Simončič report.

1.61 25.Feb.2011
gifsicle: Add new -O3 optimization level, which applies several transparency heuristics and picks the one with the best result. David Jamroga pointed out a file that gifsicle made larger; -O3 shrinks it.

gifsicle: Correct some optimizer bugs introduced in 1.59 that could lead to visually different output.

gifdiff: Add -w/--ignore-redundancy option.

gifview: Correct crash bug.

gifsicle/gifdiff: Correct occasionally odd error messages.

1.60 12.Apr.2010
GIF reading library: Correct error that could corrupt the reading of certain large images. Reported by Jernej Simončič.

1.59 11.Mar.2010
gifsicle -O2: Optimize away entirely-transparent frames when possible. Requested by Gerald Johanson.

1.58 14.Jan.2010
gifsicle: Fix optimizer bug reported by Dion Mendel.

1.57 11.Nov.2009
gifsicle: Don’t throw away totally-cropped frames with 0 delay, since most browsers treat 0-delay frames as 100ms-delay frames. Reported by Calle Kabo.

1.56 18.Oct.2009
gifsicle: Fix --crop-transparency for animated images; previous versions could lose frames. Problem reported by Daniel v. Dombrowski.

gifview: Make --disposal=background behavior look like Firefox.

1.55 3.Apr.2009
gifsicle: Another optimize fix for --disposal previous. Reported by Gerald Johanson.

1.54 3.Apr.2009
gifsicle, gifview: Fix several serious bugs with --disposal previous that could affect optimized, unoptimized, and displayed images. Reported by Gerald Johanson.

1.53 19.Mar.2009
gifsicle: Frames in an unoptimized image will use disposal "none" when possible. This leads to fewer surprises later.

1.52 18.May.2008
gifsicle: Fix bug introduced in 1.51: --crop-transparent works. Reported by dgdd wanadoo fr.

1.51 12.May.2008
gifsicle: ‘--crop’ preserves the logical screen when it can. Reported by Petio Tonev.

1.50 7.May.2008
gifsicle, gifview: Refuse to read GIFs from the terminal. Requested by Robert Riebisch.

1.49 2.May.2008
Just some Makefile updates requested by Robert Riebisch.

1.48 16.Mar.2007
gifsicle: Avoid crash in ‘--crop-transparency’ when an image’s first frame is totally transparent. Reported by Gerald Johanson.

1.47 10.Mar.2007
gifsicle: Improve ‘--nextfile’ behavior.

1.46 9.Jan.2007
gifsicle: Add ‘--nextfile’ option, useful for scripts. Problem reported by Jason Young.

1.45 30.Dec.2006
Do not compile gifview by default when X is not available.

gifview: Add ‘--title’ option, based on patch supplied by Andres Tello Abrego.

1.44 3.Oct.2005
gifview: Enforce a minimum delay of 0.002 sec. Requested by Dale Wiles.

1.43 8.Sep.2005
’-I -b’, and other similar combinations, causes a fatal error rather than putting information in an unexpected file. Reported by Michiel de Bondt.

1.42 8.Jan.2005
Improve manual page.

1.41 19.Aug.2004
Fix problems with 64-bit machines. Thanks to Dan Stahlke for pointing out the problem and providing a patch.

1.40 28.Aug.2003
Fix longstanding bug where ‘--disposal=previous’ was mistakenly equivalent to ‘--disposal=asis’.

Include Makefile.bcc, from Stephen Schnipsel.

1.39 11.Jul.2003
Fix Makefile.w32 (oops).

1.38 26.Jun.2003
Include Makefile.w32 (oops).

1.37 11.Feb.2003
Fix bug where combining ‘--rotate-X’ and ‘-O’ options would cause a segmentation fault. Reported by Dan Lasley <>.

Rearrange source tree.

1.36 17.Nov.2002
Fix subscript-out-of-range error in main.c reported by Andrea Suatoni.

1.35 14.Aug.2002
Fixed bug where ‘--crop’ could cause a segmentation fault, present since 1.32 or 1.33. Reported by Tom Schumm <>.

1.34 13.Aug.2002
Fixed bug where combining ‘--crop’ and ‘-O’ options could corrupt output. Reported by Tom Schumm <>.

1.33 1.Aug.2002
Be more careful about time while animating. In particular, prepare frames before they are needed, so that they can be displayed exactly when required. Problem reported by Walter Harms <>.

More warning fixes.

1.32 5.Jul.2002
Add ‘--multifile’ option handling concatenated GIF files. This is useful for scripts. For example, ‘gifsicle --multifile -’ will merge all GIF files written to its standard input into a single animation.

More fixes for spurious background warnings.

1.31 17.Jun.2002
Changed behavior of ‘--crop X,Y+WIDTHxHEIGHT’ option when WIDTH or HEIGHT is negative. Previously, zero or negative WIDTH and HEIGHT referred to the image’s entire width or height. Thus, the option ‘--crop 10,0+0x0’ would always lead to an error, because the crop left position (10) plus the crop width (the image width) was 10 pixels beyond the image edge. The new behavior measures zero or negative WIDTH and HEIGHT relative to the image’s bottom-right corner.

Changed background behavior. Hopefully the only user-visible effect will be fewer spurious warnings.

Fixed a bug that could corrupt output when optimizing images with ‘-O2’ that had more than 256 colors.

1.30 27.Jul.2001
Fixed bug in ungif code: Writing a large ungif could corrupt memory, leading eventually to bad output. This bug has been present since Gifsicle could write ungifs! Bad files and assistance provided by Jeff Brown <>.

1.29 22.May.2001
Fixed an optimization bug that could produce bad images. Again, reported by Dale Wiles <>. It turns out that 1.26 was a bad release! I’ve reconstructed and run some regression tests; hopefully Dale and I have exhausted the bug stream.

1.28 13.May.2001
--colors’ option still didn’t work; it produced bad images. Again, thanks to Dale Wiles <> for reporting the bug.

Added explicit ‘--conserve-memory’ option.

1.27 10.May.2001
Fixed ‘--colors’ option, which caused segmentation faults. Thanks to Dale Wiles <> for reporting the bug.

1.26 22.Apr.2001
Added ‘--crop-transparency’ option, which crops any transparent edges off the image. Requested by Gre7g Luterman <>.

Try to conserve memory in gifsicle when working with huge images (> 20 megabytes of uncompressed data). May make gifsicle slower if you actually had enough memory to deal with the uncompressed data.

1.25 13.Feb.2001
Fixed gifview bug: If every frame in an animation had a small or zero delay, then gifview would previously enter a infinite loop and become noninteractive. Reported by Franc,ois Petitjean <>.

1.24 11.Feb.2001
Delete ‘unoptimized_pixmaps’ array when deleting a viewer in gifview. Reported by Franc,ois Petitjean <>.

Added ‘--resize-width’ and ‘--resize-height’ options.

Why is it that Frenchmen are always telling me to delete the Clp_Parser immediately before calling exit()? Don’t they realize that exit() frees application memory just as well as free()? Are things different in France? More French, perhaps?

1.23 12.Dec.2000
In Houston on a layover because of stupid Continental Airlines: allow GIFs without terminators. Problem reported by Matt Olech <>.

1.22 23.Nov.2000
Handle time more carefully when displaying animations. Should result in more precise timings. Problem reported by Iris Baye <>.

1.21 9.Sep.2000
Fixed ‘--careful -O2’, which could create bad GIFs when there were bad interactions with transparency. Bug reported by Manfred Schwarb <>.

1.20 23.Jun.2000
Added ‘--careful’ option, because some bad GIF implementations (Java, Internet Explorer) don’t support Gifsicle’s super-optimized, but legal, GIFs. Problem reported by Andrea Beiser <>.

Gifdiff will work on very large images (better memory usage).

1.19 25.Apr.2000
Fixed memory corruption bug: ‘gifsicle --use-colormap=FILE.gif’ would formerly cause a segmentation fault. Bug reported by Alan Watts <>.

1.18 3.Apr.2000
Gifview now uses X server memory more parsimoniously. This should make it more robust, and nicer to the X server, on large animations. Requested by Vladimir Eltsov <>. Appears to solve bug reported by Vince McIntyre <>.

Gifview treats frame selection more sensibly. A frame selection just tells it which frame to start on.

Added a message to the manual page warning people to quote the ‘#’ character in frame selections. The interactive bash shell, for example, interprets it as a comment.

1.17 15.Mar.2000
Added ‘--resize _xH’ and ‘--resize Wx_’. Requested by Edwin Piekart <>.

Changed behavior of ‘--no-logical-screen’. Now gifsicle will include all visible GIFs when calculating the size of the logical screen.

Got rid of spurious redundant-option warnings.

1.16.1 10.Sep.1999
Gifview can put a GIF (or an animated GIF) on the root window; use ‘gifview -w root’. Requested by Roland Blais <>.

1.16 31.Aug.1999
Optimization improvement: More colormap manipulation. Version 1.16 produces smaller GIFs than 1.15 in the large majority of cases (but not all).

Fixed memory corruption bug in quantization. Found and fixed by Steven Marthouse <>.

1.15 20.Aug.1999
Bug fix: no more assertion failures when combining images that require local colormaps.

Fixed serious quantization bug introduced in 1.14: when reducing the number of colors, gifsicle would ignore a random portion of the colors in the old colormap.

Optimization bug fix: two adjacent identical frames will no longer crash the optimizer. Bug introduced in 1.14. That’s two for two: two "speed improvements" in 1.14, two bugs introduced!

Bug fix: Exploding the standard input results in files named ‘#stdin#.NNN’, as the documentation claims, not ‘<stdin>.NNN’.

Optimization improvement: the optimizer reorders colormaps in a slightly smarter way, which can result in smaller compression.

If a position option like ‘-p 0,5’ is followed by a multi-frame GIF (without frame specifications), then the position option places the animation as a whole, not each of its individual frames.

An unrecognized nonnumeric frame specification is now treated as a file name, so you can say ‘gifsicle #stdin#.000’, for example.

Gifview improvements: Now even images with local color tables can be "unoptimized" or animated.

--replace’ now preserves the replaced frame’s disposal as well as its delay.

gifsicle -I -’ reports "<stdin>" as the input file name.

1.14.2 16.Aug.1999
Fixed memory bug in Gif_DeleteImage (I freed a block of memory, then accessed it). I am a moron!! This bug affected Version 1.14.1 only.

1.14.1 9.Aug.1999
Fixed configuration bug: you couldn’t compile gifsicle from a different directory (it told you to try --enable-ungif).

Steven Marthouse <> helped fix ‘Makefile.w32’ to enable wildcards in filenames under Windows. Requested by Mark Olesen <>.

1.14 2.Aug.1999
Switched to an adaptive tree strategy for LZW GIF compression, which is faster than the old hashing strategy. This method is the brainchild of Hans Dinsen-Hansen <>.

Bug fix/optimization improvement: Some images would include a transparent index that was not a valid color (it was larger than the colormap). Gifsicle formerly ignored these transparent indices. It doesn’t any longer; furthermore, it will generate those kinds of transparent index, which can mean smaller colormaps and smaller GIFs.

Speed improvements in optimization and colormap quantization.

Added ‘--no-warnings’ (‘-w’) option to inhibit warning messages. Suggested by Andrea Beiser <>.

--info’ output can now be sent to a file with ‘-o’, just as with any other kind of output.

More specific error messages on invalid GIFs.

1.13 16.Jun.1999
Added optional support for run-length-encoded GIFs to avoid patent problems. Run-length encoding idea based on code by Hutchinson Avenue Software Corporation <> found in Thomas Boutell’s gd library <>.

gifsicle --explode’ now generates filenames of the form ‘file.000 .. file.100’ rather than ‘file.0 .. file.100’, so you can use shell globbing like ‘file.*’ and automatically get the right order.

Added ‘--background’ option to gifview, so you can set the color used for transparent pixels. Suggested by Art Blair <>.

Gifdiff is built by default on Unix.

1.12 25.Mar.1999
Added ‘--window’ option to gifview, which lets it display a GIF in an arbitrary X window. Thanks to Larry Smith <> for patches.

Added ‘--install-colormap’ to gifview. Suggested by Yair Lenga <>.

Gifsicle now exits with status 1 if there were any errors, status 0 otherwise. Before, it exited with status 1 only if there was a fatal error, or nothing was successfully output. The new behavior seems more useful. Problem reported by David Kelly <>.

1.11.2 10.Mar.1999
gifsicle -U’ will now unoptimize 1-image GIFs as well as animations.

1.11.1 24.Jan.1999
Fixed core dump on corrupted GIF files (in particular, bad extensions). Problem reported by tenthumbs <>.

1.11 22.Jan.1999
Added ‘--scale XFACTORxYFACTOR’ to complement ‘--resize’.

Made ‘--resize’ work better on animations (no more off-by-one errors).

Fixed bug in ‘--use-colormap’: If transparency was added to the new colormap, the transparent color index could later be used (incorrectly) as a real image color. This was particularly common if the image was dithered.

--dither’ now tries to mitigate "jumping dither" animation artifacts (where adjacent frames in an animation have different dithering patterns, so the animation shifts). It does an OK job.

Improvements to ‘--color-method=blend-diversity’.

1.10 6.Jan.1999
Gifview is built by default.

No other changes from 1.10b1: Emil said it worked on Windows.

1.10b1 31.Dec.1998
The two malloc packages that come with Gifsicle don’t #define ‘malloc’ or ‘realloc’; they #define ‘xmalloc’ and ‘xrealloc’.

Changes to Windows port from Emil Mikulic <>.

1.9.2 28.Dec.1998
Gifsicle compiles out of the box on Windows! Port maintained by Emil Mikulic <>.

Moved to config.h-based configuration to simplify GIF library and Windows port.

Some CLP improvements.

1.9.1 16.Dec.1998
If a reduced-colormap image needs a special transparent color, gifsicle will now try to keep the same transparent color value as the input GIF.

Cropping an image now automatically recalculates the output logical screen, rather than retaining the logical screen of the uncropped image.

Improvement to colormap modification behavior: If it looks like a color reserved for transparency will be necessary, gifsicle will reserve a slot for it. This will reduce the likelihood that you ask for a colormap of size 64, say, and get one of size 128 (because gifsicle added a slot for transparency).

1.9 14.Dec.1998
--no-background’ is now the same as ‘--background=0’ (set the background to pixel 0) instead of ‘--same-background’.

1.9b3 10.Dec.1998
Fixed a serious bug in merge.c introduced in 1.8: Merging several images with global colormaps could corrupt the output colors.

Fixed a serious bug in optimize.c introduced in 1.9b1: Optimizing GIFs which required local color tables could crash the program due to a buffer overrun. (I was adding the background to the output colormap without making sure there was room for it.)

Fixed an optimizer bug which could result in incorrect animations: background disposal was not handled correctly.

The optimizer now generates ‘--disposal=none’ instead of ‘--disposal=asis’ in certain situations, which can result in smaller animations. Suggestion by Markus F.X.J. Oberhumer <>.

GIF library changes: cleaner, somewhat faster GIF reading code inspired by Patrick J. Naughton <>, whose code is distributed with XV.

1.9b2 9.Dec.1998
Fixed ‘--logical-screen’ and ‘--no-logical-screen’, which had no effect in 1.9b1. In a stunning turn of events, this problem was reported by Markus F.X.J. Oberhumer <>.

1.9b1 5.Dec.1998
Added ‘--resize WxH’ option, prompted by code from Christian Kumpf <>.

Made ‘--change-color PIXELINDEX color’ work, and ‘--change-color color PIXELINDEX’ illegal.

Many behavior fixes relating to background and transparency. Gifsicle would tend to create GIFs which looked as expected, but lost information internally; for example, a color value which was only used for transparency would be changed to black, no matter what the input color was. In some cases, gifsicle simply reports a warning now where it ignored information before. Problems reported by Markus F.X.J. Oberhumer <>.

Better error messages are now given on redundant, ambiguous, or useless command-line options.

Options that affect GIFs on output (such as ‘--output’, ‘--optimize’) now behave more like other options: you should put them before the files they affect. (You may still put them at the end of the argument list if they should affect the last output file.) This should only affect people who used batch or explode mode in complex ways.

Gifsicle will not write a GIF to stdout if it’s connected to a terminal.

1.8 3.Dec.1998
Fixed strange behavior when changing transparency: a new black entry was added to the colormap in almost all situations. Problem reported by Markus F.X.J. Oberhumer <>.

Fixed ‘--transform-colormap’ bug: commands like "thing 2" (ending in an integer) will work now.

Small fixes (in a gifsicle pipeline, error messages won’t be interleaved).

1.7.1 2.Dec.1998
Added configuration check for ‘strerror’. Problem reported by Mario Gallotta <>.

Added colormap canonicalization: If you pipe a GIF through ‘gifsicle -O’ or ‘-O2’, the output colormaps will be arranged in a predictable order. Feature suggested by Markus F.X.J. Oberhumer <>.

1.7 28.Nov.1998
Added ‘--use-colormap=gray’ and ‘--use-colormap=bw’. Idea and some code thanks to Christian Kumpf <>.

Added ‘--transform-colormap’, which allows you to plug programs into gifsicle that arbitrarily change GIF files’ colormaps.

All ‘--change-color’ options now happen simultaneously, so you can safely swap two colors with ‘--change-color C1 C2 --change-color C2 C1’.

Colormap modifications are slightly more powerful (they don’t reserve a color for transparency if they don’t need one, and if a subset of the modified colormap is used, only that subset is output).

Fixed ‘--use-colormap’ bug: the last color in a used colormap would be ignored (it was reserved for transparency). Symptom: if you put a partially transparent image into the Web-safe palette, the result would never contain white.

When changing to a grayscale colormap, gifsicle now uses luminance difference to find the closest color. This gives better results for ‘--use-colormap=gray’ and the like.

Added Introduction and Concept Index sections to the gifsicle manpage.

The gifsicle package now uses automake.

1.6 23.Nov.1998
A frame extracted from the middle of an animation will now have the animation’s screen size rather than 640x480. Problem reported by Mr. Moose <>.

1.5 27.Sep.1998
--help’ now prints on stdout, as according to the GNU standards.

Changes to support Win32 port thanks to Emil Mikulic <>.

Makefiles: Added ‘make uninstall’ target, enabled ‘./configure”s program name transformations, made VPATH builds possible.

1.4.1 16.Sep.1998
Fixed ‘--unoptimize’ bug: a frame’s transparency could disappear under rare circumstances. Bug reported by Rodney Brown <>

1.4 12.Sep.1998
Added ‘--extension’ and ‘--app-extension’.

1.3.4 7.Sep.1998
More configuration changes.

Fixed bug in gifview ‘--geometry’ option processing: ‘--geometry -0-0’ wasn’t recognized.

1.3.2 5.Sep.1998
Fixed configuration bugs reported by Alexander Mai <> (OS/2 build didn’t work).

1.3.1 4.Sep.1998
Fixed configuration bug: int32_t could be improperly redefined. Reported by Anne "Idiot" Dudfield <> and Dax Kelson <>.

1.3 3.Sep.1998
Added ‘--flip-*’ and ‘--rotate-*’ options.

Fixed rare bug in GIF writing code: the last pixel in a frame could previously become corrupted.

1.3b1 2.Aug.1998
Optimization has been completely overhauled. All optimization functions are in a separate file, optimize.c. Some bugs have been caught. Optimization is now quite powerful, and rarely expands any input file. (An expansion of 1-30 bytes usually means that the input file cheated by leaving off ’end-of-image’ codes, which the standard says must be used.) People interested in making optimization even better should contact me, or just go ahead and hack the code. Thanks again to David Hedbor <> for providing test cases.

Specific changes:

- The optimizer can handle any input file, even one with local colormaps or more than 256 colors. If there are more than 256 colors, an optimal subset is placed in the global colormap.

- The global colormap is reordered so that some images can use a small initial portion of it, which lets them compress smaller.

- Bug fix: Images relying on background disposal are optimized correctly.

- ‘-O2’ never does worse than ‘-O1’.

- Made the ‘-O2’ heuristic better. Some other small changes and improvements here and there.

- The optimizer has been pretty extensively tested using gifdiff.

New program: gifdiff compares two GIFs for identical appearance. It is not built unless you give the ‘--enable-gifdiff’ option to ‘./configure’. It’s probably not useful unless you’re testing a GIF optimizer.

Robustness fixes in GIF library.

1.2.1 8.Jun.1998
--info’ now sends information to standard output. ‘--info --info’ still sends information to standard error.

--transparent’ didn’t work. It does now.

Added ‘--background’ option. Fixed background processing so that an input background is reflected in the output GIF.

Re-fixed small bug with the interaction between per-frame options and frame selections.

1.2 28.May.1998
Fixed small bug with the interaction between per-frame options (‘--name’, ‘--comment’) and frame selections.

Fixed bad bug in merge: If a global colormap from the source needed to be dumped into a local colormap in the destination, the pixel map was wrong, resulting in bad colors in the destination.

Fixed memory leaks. Changed memory usage pattern in gifsicle to release source image memory as soon as possible, resulting in a better memory profile. Both programs now keep images in compressed form for better performance.

Fixed bugs in gifread.c that corrupted memory when uncompressing some bad images.

Added debugging malloc library (‘./configure --enable-dmalloc’ to use it).

Added ‘--no-delay’ and ‘--no-disposal’ options, which should have been there all along.

--crop’ will not generate an image with 0 width or height, even if a frame is cropped out of existence.

Other performance improvements.

1.2b6 25.May.1998
License clarification in README.

GIF comments are now printed out more carefully in ‘--info’: binary characters appear as backslash escapes. (Literal backslashes are printed as ‘\\’.)

New ‘--extension-info/--xinfo’ option.

Removed spurious warning about local colormaps when a ‘--colors’ option is in effect.

Replacing a named frame with another image now keeps the name by default.

Many changes to gifview. Added ‘--animate’, ‘--display’, ‘--geometry’, ‘--name’, ‘--help’ options, keystrokes, multiple GIFs on the command line, and a manual page.

1.2b5 12.May.1998
Longstanding bug fix in gifunopt.c: an interlaced replacement frame caused strange behavior when later optimizing, as the underlying data wasn’t deinterlaced.

Further improvements in optimizer; specifically, ‘-O2’ works better now -- it uses actual image data to look for an unused pixel value when there’s no transparency specified.

1.2b4 12.May.1998
Improved ‘--optimize”s performance on images where successive frames had different transparent color indexes.

1.2b3 11.May.1998
Fixed bugs in ‘--unoptimize’: it would try to unoptimize images with local color tables and some transparency manipulations could cause a silent failure (example: 2 colors; frame 0 = [*11], frame 1 = [*0*], where * is a transparent pixel. Unoptimized, frame 1 should contain [*01] -- but this can’t be expressed with only 2 colors.)

Greatly improved ‘--optimize”s performance on some images by changing the way frames were switched to ‘--disposal=background’. Problem noticed by David Hedbor <>

Documentation improvements.

Unrecognized extensions are now passed through without change. The ‘--no-extensions’ option (currently undocumented) removes all unrecognized extensions.

Bug fix in gifview: frame selections now prevent display of entire GIF.

1.2b2 9.May.1998
Fixed bad dumb bug in gif.h: lack of parens around macro argument

Changed heuristic for diversity algorithm: never blend if there are 3 colors or less

Some optimizations to Floyd-Steinberg code

1.2b1 8.May.1998
Added colormap options: ‘--colors’, ‘--color-method’, ‘--dither’, and ‘--use-colormap’. All this code is in quantize.c.

Renamed ‘--color-change’ to ‘--change-color’.

Added ‘--color-change’ option.

Added negative frame numbers. ‘#-N’ no longer means ‘#0-N’; it means the ‘N’th frame from the end (where ‘#-1’ is the last frame). You can use negative frame numbers in ranges as well (e.g., ‘#-5--1’).

1.1.1 22.Nov.1997
Fixed bug in CLP which segmentation-faulted on ‘-’ arguments.

1.1 20.Nov.1997
Added ‘--crop’ option.

Changed usage behavior on bad command lines.

1.0 21.Jun.1997
Added ‘--output/-o’ option to specify output filename.

Slight behavior change: Now, if you replace a frame (say frame #2), its delay value will be preserved in the replacement frame, unless you give an explicit delay. (Before, the replacement frame’s delay would be used, which was probably 0.)

0.91 15.Jun.1997
Bug fix: ‘--optimize’ didn’t handle the bottom row of an image’s changed area correctly. This could lead to incorrect animations. Specific change: merge.c line 744: was y < fbt, now y <= fbt.

Added ‘-S’ as synonym for ‘--logical-screen’.

0.9 12.Jun.1997
First public release.