gifsicle(1)
NAME
gifsicle - manipulates GIF images and animations
SYNOPSIS
gifsicle [options, frames, and filenames]...
DESCRIPTION
gifsicle is a powerful command-line program for creating, editing,
manipulating, and getting information about GIF images and animations.
Gifsicle normally processes input GIF files according to its command
line options and writes the result to the standard output. The -i
option, for example, tells gifsicle to interlace its inputs:
gifsicle -i < pic.gif > interlaced-pic.gif
Gifsicle is good at creating and manipulating GIF animations. By
default, it combines two or more input files into a "flipbook"
animation:
gifsicle pic1.gif pic2.gif pic3.gif > animation.gif
Use options like --delay, --loopcount, and --optimize to tune your
animations.
To modify GIF files in place, use the --batch option. With --batch,
gifsicle will modify the files you specify instead of writing a new
file to the standard output. To interlace all the GIFs in the current
directory, you could say:
gifsicle --batch -i *.gif
New users may want to skip to the Examples section at the end.
CONCEPT INDEX
Concepts are on the left, relevant gifsicle options are on the right.
Animations, changing frame selections, frame changes, etc.
disposal --disposal
looping --loopcount
portions of frame selections
smaller --optimize, --colors
speed --delay
Bad output --careful
Background color --background
Colors, changing --change-color, --use-colormap, --dither,
--transform-colormap
reducing number --colors, --dither, --gamma
Comments --comment
Extensions --extension, --app-extension, --extension-info
File size --optimize, --unoptimize, --colors
Image transformations
cropping --crop, --crop-transparency
flipping --flip-*
resizing --resize, --scale
rotating --rotate-*
Grayscale --use-colormap
Interlacing --interlace
Positioning frames --position
Screen, logical --logical-screen
Selecting frames frame selections (like '#0')
Transparency --transparent
Warnings --no-warnings
COMMAND LINE
gifsicle's command line consists of GIF input files and options. Most options start with a dash (-) or plus (+); frame selections, a kind of option, start with a number sign (#). Anything else is a GIF input file. gifsicle reads and processes GIF input files in order. If no GIF input file is given, or you give the special filename '-', it reads from the standard input. gifsicle exits with status 0 if there were no errors and status 1 otherwise.
OPTIONS
Every option has a long form, '--long-descriptive-name'. You don't
need to type the whole long descriptive name, just enough to make it
unambiguous.
Some options also have a short form, '-X'. You can combine short
options if they don't take arguments: '-IIb' is the same as '-I -I -b'.
But be careful with options that do take arguments: '-cblah' means '-c
blah', not '-c -b -l -a -h'.
Many options also have a converse, '--no-option', which turns off the
option. You can turn off a short option '-X' by saying '+X' instead.
Mode Options
Mode options tell gifsicle what kind of output to generate. There can
be at most one, and it must precede any GIF inputs.
--merge, -m
Combine all GIF inputs into one file with multiple frames and
write that file to the standard output. This is the default mode.
--batch, -b
Modify each GIF input in place by reading and writing to the same
filename. (GIFs read from the standard input are written to the
standard output.)
--explode, -e
Create an output GIF for each frame of each input file. The output
GIFs are named 'xxx.000', 'xxx.001', and so on, where 'xxx' is the
name of the input file (or whatever you specified with '--output')
and the numeric extension is the frame number.
--explode-by-name, -E
Same as --explode, but write any named frames to files 'xxx.name'
instead of 'xxx.frame-number'. Frames are named using the
'--name' option.
General Options
General options control the information gifsicle prints and where it
writes its output. The info options and --verbose can be turned off
with '--no-X'.
--info, -I
Print a human-readable description of each input GIF to the
standard output, or whatever file you specify with -o. This
option suppresses normal output, and cannot be combined with mode
options like --batch. If you give two --info or -I options,
however, information is printed to standard error, and normal
output takes place as usual.
--color-info, --cinfo
Like --info, but also print information about input files'
colormaps.
--extension-info, --xinfo
Like --info, but also print any unrecognized GIF extensions in a
hexdump(1)-like format.
--size-info, --sinfo
Like --info, but also print information about compressed image
sizes.
--help, -h
Print usage information and exit.
-o file
--output file
Send output to file. The special filename '-' means the standard
output.
--verbose, -V
Print progress information (files read and written) to standard
error.
--no-warnings, -w
Suppress all warning messages.
--no-ignore-errors
Exit with status 1 when encountering a very erroneous GIF. Default
is to muddle on.
--version
Print the version number and some short non-warranty information
and exit.
--careful
Write slightly larger GIFs that avoid bugs in some other GIF
implementations. Some Java and Internet Explorer versions cannot
display the correct, minimal GIFs that Gifsicle produces. Use the
--careful option if you are having problems with a particular
image.
--conserve-memory
Conserve memory usage at the expense of processing time. This may
be useful if you are processing large GIFs on a computer without
very much memory.
--nextfile
Allow input files to contain multiple concatenated GIF images. If
a filename appears multiple times on the command line, gifsicle
will read a new image from the file each time. This option can
help scripts avoid the need for temporary files. For example, to
create an animated GIF with three frames with different delays,
you might run "gifsicle --nextfile -d10 - -d20 - -d30 - > out.gif"
and write the three GIF images, in sequence, to gifsicle's
standard input.
--multifile
Like --nextfile, but read as many GIF images as possible from each
file. This option is intended for scripts. For example, to merge
an unknown number of GIF images into a single animation, run
"gifsicle --multifile - > out.gif" and write the GIF images, in
sequence, to gifsicle's standard input. Any frame selections
apply only to the last file in the concatenation.
Frame Selections
A frame selection tells gifsicle which frames to use from the current
input file. They are useful only for animations, as non-animated GIFs
only have one frame. Here are the acceptable forms for frame
specifications.
#num Select frame num. (The first frame is '#0'. Negative
numbers count backwards from the last frame, which is
'#-1'.)
#num1-num2 Select frames num1 through num2.
#num1- Select frames num1 through the last frame.
#name Select the frame named name.
The '#' character has special meaning for many shells, so you generally
need to quote it.
For example,
gifsicle happy.gif "#0"
uses the first frame from happy.gif;
gifsicle happy.gif "#0-2"
uses its first three frames; and
gifsicle happy.gif "#-1-0"
uses its frames in reverse order (starting from frame #-1 -- the last
frame -- and ending at frame #0 -- the first).
The action performed with the selected frames depends on the current
mode. In merge mode, only the selected frames are merged into the
output GIF. In batch mode, only the selected frames are modified; other
frames remain unchanged. In explode mode, only the selected frames are
exploded into output GIFs.
Frame Change Options
Frame change options insert new frames into an animation or replace or
delete frames that already exist. Some things -- for example, changing
one frame in an animation -- are difficult to express with frame
selections, but easy with frame changes.
--delete frames [frames...]
Delete frames from the input GIF.
--insert-before frame other-GIFs
Insert other-GIFs before frame in the input GIF.
--append other-GIFs
Append other-GIFs to the input GIF.
--replace frames other-GIFs
Replace frames from the input GIF with other-GIFs.
--done
Complete the current set of frame changes.
The frames arguments are frame selections (see above). These arguments
always refer to frames from the original input GIF. So, if 'a.gif' has
3 frames and 'b.gif' has one, this command
gifsicle a.gif --delete "#0" --replace "#2" b.gif
will produce an output animation with 2 frames: 'a.gif' frame 1, then
'b.gif'.
The other-GIFs arguments are any number of GIF input files and frame
selections. These images are combined in merge mode and added to the
input GIF. The other-GIFs last until the next frame change option, so
this command replaces the first frame of 'in.gif' with the merge of
'a.gif' and 'b.gif':
gifsicle -b in.gif --replace "#0" a.gif b.gif
This command, however, replaces the first frame of 'in.gif' with
'a.gif' and then processes 'b.gif' separately:
gifsicle -b in.gif --replace "#0" a.gif --done b.gif
Warning: You shouldn't use both frame selections and frame changes on
the same input GIF.
Image Options
Image options modify input images -- by changing their interlacing,
transparency, and cropping, for example. Image options have three
forms: '--X', '--no-X', and '--same-X'. The '--X' form selects a value
for the feature, the '--no-X' form turns off the feature, and the
'--same-X' form means that the feature's value is copied from each
input. The default is always '--same-X'. For example,
-background="#0000FF" sets the background color to blue,
--no-background turns the background color off (by setting it to 0),
and --same-background uses input images' existing background colors.
You can give each option multiple times; for example,
gifsicle -b -O2 -i a.gif --same-interlace b.gif c.gif
will make 'a.gif' interlaced, but leave 'b.gif' and 'c.gif' interlaced
only if they were already.
-B color
--background color
Set the output GIF's background to color. The argument can have
the same forms as in the --transparent option below.
--crop x1,y1-x2,y2
--crop x1,y1+widthxheight
Crop the following input frames to a smaller rectangular area. The
top-left corner of this rectangle is (x1,y1); you can give either
the lower-right corner, (x2,y2), or the width and height of the
rectangle. In the x1,y1+widthxheight form, width and height can be
zero or negative. A zero dimension means the cropping area goes to
the edge of the image; a negative dimension brings the cropping
area that many pixels back from the image edge. For example,
--crop 2,2+-2x-2 will shave 2 pixels off each side of the input
image. Cropping takes place before any rotation, flipping,
resizing, or positioning.
--crop-transparency
Crop any transparent borders off the following input frames. This
happens after any cropping due to the --crop option. It works on
the raw input images; for example, any transparency options have
not yet been applied.
--flip-horizontal
--flip-vertical
Flip the following frames horizontally or vertically.
-i
--interlace
Turn interlacing on.
-S widthxheight
--logical-screen widthxheight
Set the output logical screen to widthxheight.
--no-logical-screen sets the output logical screen to the size of
the largest output frame, while --same-logical-screen sets the
output logical screen to the largest input logical screen.
--screen is a synonym for --logical-screen.
-p x,y
--position x,y
Set the following frames' positions to (x,y). --no-position means
--position 0,0. Normally, --position x,y places every succeeding
frame exactly at x,y. However, if an entire animation is input,
x,y is treated as the position for the animation.
--rotate-90
--rotate-180
--rotate-270
Rotate the following frames by 90, 180, or 270 degrees.
--no-rotate turns off any rotation.
-t color
--transparent color
Make color transparent in the following frames. Color can be a
colormap index (0-255), a hexadecimal color specification (like
"#FF00FF" for magenta), or slash- or comma-separated red, green
and blue values (each between 0 and 255).
Extension Options
Extension options add non-visual information to the output GIF. This
includes names, comments, and generic extensions.
--app-extension app-name extension
Add an application extension named app-name and with the value
extension to the output GIF. --no-app-extensions removes
application extensions from the input images.
-c text
--comment text
Add a comment, text, to the output GIF. The comment will be placed
before the next frame in the stream. --no-comments removes
comments from the input images.
--extension number extension
Add an extension numbered number and with the value extension to
the output GIF. Number can be in decimal, octal, hex, or it can
be a single character like 'n', whose ASCII value is used.
--no-extensions (or +x) removes extensions from the input images.
-n text
--name text
Set the next frame's name to text. This name is stored as an
extension in the output GIF (extension number 0xCE, followed by
the characters of the frame name). --no-names removes name
extensions from the input images.
Animation Options
Animation options apply to GIF animations, or to individual frames in
GIF animations. As with image options, most animation options have
three forms, '--X', '--no-X', and '--same-X', and you can give
animation options multiple times; for example,
gifsicle -b a.gif -d50 "#0" "#1" -d100 "#2" "#3"
sets the delays of frames 0 and 1 to 50, and frames 2 and 3 to 100.
-d time
--delay time
Set the delay between frames to time in hundredths of a second.
-D method
--disposal method
Set the disposal method for the following frames to method. A
frame's disposal method determines how a viewer should remove the
frame when it's time to display the next. Method can be a number
between 0 and 7 (although only 0 through 3 are generally
meaningful), or one of these names: none (leave the frame visible
for future frames to build upon), asis (same as "none"),
background (or bg) (replace the frame with the background), or
previous (replace the frame with the area from the previous
displayed frame). --no-disposal means --disposal=none.
-l[count]
--loopcount[=count]
Set the Netscape loop extension to count. Count is an integer, or
forever to loop endlessly. If you supply a --loopcount option
without specifying count, Gifsicle will use forever.
--no-loopcount (the default) turns off looping.
Set the loop count to one less than the number of times you want
the animation to run. An animation with --no-loopcount will show
every frame once; --loopcount=1 will loop once, thus showing every
frame twice; and so forth. Note that --loopcount=0 is equivalent
to --loopcount=forever, not --no-loopcount.
-O[level]
--optimize[=level]
Optimize output GIF animations for space. Level determines how
much optimization is done; higher levels take longer, but may have
better results. There are currently three levels:
-O1 Stores only the changed portion of each image. This is the
default.
-O2 Also uses transparency to shrink the file further.
-O3 Try several optimization methods (usually slower, sometimes
better results).
Other optimization flags provide finer-grained control.
-Okeep-empty
Preserve empty transparent frames (they are dropped by
default).
You may also be interested in other options for shrinking GIFs,
such as -k and --no-extensions.
-U
--unoptimize
Unoptimize GIF animations into an easy-to-edit form.
GIF animations are often optimized (see --optimize) to make them
smaller and faster to load, which unfortunately makes them
difficult to edit. --unoptimize changes optimized input GIFs into
unoptimized GIFs, where each frame is a faithful representation of
what a user would see at that point in the animation.
Image Transformation Options
Image transformation options apply to entire GIFs as they are read or
written. They can be turned off with '--no-option'.
--resize widthxheight
Resize the output GIF to widthxheight. Either width or height may
be an underscore '_'. If the argument is widthx_, then the output
GIF is scaled to width pixels wide without changing its aspect
ratio. An analogous operation is performed for _xheight. Resizing
happens after all input frames have been combined and before
optimization. Resizing uses logical screen dimensions; if the
input stream has an unusual logical screen (many GIF displayers
ignore logical screens), you may want to provide
--no-logical-screen (or +S) to reset it so gifsicle uses image
dimensions instead. See also --resize-method.
--resize-width width
--resize-height height
Like --resize widthx_ and --resize _xheight respectively.
--resize-fit widthxheight
Like --resize, but resizes the output GIF to fit within a
rectangle with dimensions widthxheight. The GIF's aspect ratio
remains unchanged. No resize is performed if the GIF already fits
within the given rectangle. Either width or height may be an
underscore '_', which is treated as infinity.
--resize-fit-width width
--resize-fit-height height
Like --resize-fit widthx_ and --resize-fit _xheight respectively.
--scale Xfactor[xYfactor]
Scale the output GIF's width and height by Xfactor and Yfactor.
If Yfactor is not given, it defaults to Xfactor. Scaling happens
after all input frames have been combined and before optimization.
--resize-method method
Set the method used to resize images. The 'sample' method runs
very quickly, but when shrinking images, it produces noisy
results. The 'mix' method is somewhat slower, but produces
better-looking results. The default method is currently 'mix'.
Details: The resize methods differ most when shrinking images. The
'sample' method is a point sampler. Each pixel position in the
output image maps to exactly one pixel position in the input, so
when shrinking, full rows and columns from the input are dropped.
The other methods use all input pixels, which generally produces
better-looking images. The 'box' method, a box sampler, is faster
than the more complex filters and produces somewhat sharper
results, but there will be anomalies when shrinking images by a
small amount in one dimension. (Some output pixels will
correspond to exactly 1 input row or column, while others will
correspond to exactly 2 input rows or columns.) The 'mix' method
is a full bilinear interpolator. This is slower and produces
somewhat blurrier results, but avoids such anomalies.
Gifsicle also supports several complex resamplers, including
Catmull-Rom cubic resampling ('catrom'), the Mitchell-Netravali
filter ('mitchell'), a 2-lobed Lanczos filter ('lanczos2'), and a
3-lobed Lanczos filter ('lanczos3'). These filters are slower
still, but can give sharper, better results.
--resize-colors n
Allow Gifsicle to add intermediate colors when resizing images.
Normally, Gifsicle's resize algorithms use input images' color
palettes without changes. When shrinking images with very few
colors (e.g., pure black-and-white images), adding intermediate
colors can improve the results. Example: --resize-colors 64 allows
Gifsicle to add intermediate colors for images that have fewer
than 64 input colors.
Color Options
Color options apply to entire GIFs as they are read or written. They
can be turned off with '--no-option'.
-k num
--colors num
Reduce the number of distinct colors in each output GIF to num or
less. Num must be between 2 and 256. This can be used to shrink
output GIFs or eliminate any local color tables.
Normally, an adaptive group of colors is chosen from the existing
color table. You can affect this process with the --color-method
option or by giving your own colormap with --use-colormap.
Gifsicle may need to add an additional color (making num+1 in all)
if there is transparency in the image.
--color-method method
Determine how a smaller colormap is chosen. 'diversity', the
default, is xv(1)'s diversity algorithm, which uses a strict
subset of the existing colors and generally produces good results.
'blend-diversity' is a modification of this: some color values are
blended from groups of existing colors. 'median-cut' is the
median cut algorithm described by Heckbert. --method is a synonym
for --color-method.
-f
--dither[=method]
When --dither is on and the colormap is changed, combinations of
colors are used to approximate missing colors. This looks better,
but makes bigger files and can cause animation artifacts, so it is
off by default.
Specify a dithering algorithm with the optional method argument.
The default, 'floyd-steinberg', uses Floyd-Steinberg error
diffusion. This usually looks best, but can cause animation
artifacts, because dithering choices will vary from frame to
frame. Gifsicle also supports ordered dithering algorithms that
avoid animation artifacts. The 'ro64' mode uses a large, random-
looking pattern and generally produces good results. The 'o3',
'o4', and 'o8' modes use smaller, more regular patterns. The
'ordered' mode chooses a good ordered dithering algorithm. For
special effects, try the halftone modes 'halftone',
'squarehalftone', and 'diagonal'. Some modes take optional
parameters using commas. The halftone modes take a cell size and a
color limit: 'halftone,10,3' creates 10-pixel wide halftone cells
where each cell uses up to 3 colors.
--gamma gamma
Set the gamma correction to gamma, which can be a real number or
'srgb'. Roughly speaking, higher numbers exaggerate shadows and
lower numbers exaggerate highlights. The default is the function
defined by the standard sRGB color space, which usually works
well. (Its effects are similar to --gamma=2.2.) Gifsicle uses
gamma correction when choosing a color palette (--colors) and when
dithering (--dither).
--change-color color1 color2
Change color1 to color2 in the following input GIFs. (The color
arguments have the same forms as in the -t option.) Change
multiple colors by giving the option multiple times. Color changes
don't interfere with one another, so you can safely swap two
colors with '--change-color color1 color2 --change-color color2
color1'. They all take effect as an input GIF is read.
--no-change-color cancels all color changes.
--transform-colormap command
Command should be a shell command that reads from standard input
and writes to standard output. Each colormap in the output GIF is
translated into text colormap format (see --use-colormap below)
and piped to the command. The output that command generates (which
should also be in text colormap format) will replace the input
colormap. The replacement doesn't consider color matching, so
pixels that used color slot n in the input will still use color
slot n in the output.
--use-colormap colormap
Change the image to use colormap. Each pixel in the image is
changed to the closest match in colormap (or, if --dither is on,
to a dithered combination of colors in colormap). Colormap can be
web for the 216-color "Web-safe palette"; gray for grayscale; bw
for black-and-white; or the name of a file. That file should
either be a text file (the format is described below) or a GIF
file, whose global colormap will be used. If --colors=N is also
given, an N-sized subset of colormap will be used.
Text colormap files use this format:
; each non-comment line represents one color, "red green blue"
; each component should be between 0 and 255
0 0 0 ; like this
255 255 255
; or use web hex notation
#ffffff ; like this
EXAMPLES
First, let's create an animation, 'anim.gif':
gifsicle a.gif b.gif c.gif d.gif > anim.gif
This animation will move very quickly: since we didn't specify a delay,
a browser will cycle through the frames as fast as it can. Let's slow
it down and pause .5 seconds between frames, using the --delay option.
gifsicle --delay 50 a.gif b.gif c.gif d.gif > anim.gif
If we also want the GIF to loop three times, we can use --loopcount:
gifsicle -d 50 --loop=3 a.gif b.gif c.gif d.gif > anim.gif
(Rather than type --delay again, we used its short form, -d. Many
options have short forms; you can see them by running 'gifsicle
--help'. We also abbreviated --loopcount to --loop, which is OK since
no other option starts with 'loop'.)
To explode 'anim.gif' into its component frames:
gifsicle --explode anim.gif
ls anim.gif*
anim.gif anim.gif.000 anim.gif.001 anim.gif.002 anim.gif.003
To optimize 'anim.gif':
gifsicle -b -O2 anim.gif
To change the second frame of 'anim.gif' to 'x.gif':
gifsicle -b --unoptimize -O2 anim.gif --replace "#1" x.gif
--unoptimize is used since 'anim.gif' was optimized in the last step.
Editing individual frames in optimized GIFs is dangerous without
--unoptimize; frames following the changed frame could be corrupted by
the change. Of course, this might be what you want.
Note that --unoptimize and --optimize can be on simultaneously.
--unoptimize affects input GIF files, while --optimize affects output
GIF files.
To print information about the first and fourth frames of 'anim.gif':
gifsicle -I "#0" "#3" < anim.gif
To make black the transparent color in all the GIFs in the current
directory, and also print information about each:
gifsicle -bII --trans "#000000" *.gif
Giving -I twice forces normal output to occur. With only one -I, the
GIFs would not be modified.
To change 'anim.gif' to use a 64-color subset of the Web-safe palette:
gifsicle -b --colors=64 --use-col=web anim.gif
To make a dithered black-and-white version of 'anim.gif':
gifsicle --dither --use-col=bw anim.gif > anim-bw.gif
To overlay one GIF atop another -- producing a one-frame output GIF
that looks like the superposition of the two inputs -- use gifsicle
twice:
gifsicle bottom.gif top.gif | gifsicle -U "#1" > result.gif
BUGS
Some optimized output GIFs may appear incorrectly on some GIF implementations (for example, Java's); see the --careful option. Please email suggestions, additions, patches and bugs to ekohler@gmail.com.
SEE ALSO
For a tutorial on GIF images and animations, you might try some of the resources listed on-line at webreference.com: http://www.webreference.com/authoring/graphics/animation.html
AUTHORS
Eddie Kohler <ekohler@gmail.com> http://www.read.seas.harvard.edu/~kohler/ He wrote it. Anne Dudfield <annied@frii.com> http://www.frii.com/~annied/ She named it. Hans Dinsen-Hansen <dino@danbbs.dk> http://www.danbbs.dk/~dino/ Adaptive tree method for GIF writing. http://www.lcdf.org/gifsicle/ The gifsicle home page.
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