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gifsicle.1
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.\" -*- mode: nroff -*-
.AM
.ds V 1.92
.ds E " \-\-
.if t .ds E \(em
.de Op
.BR "\\$1" "\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.de Oa
.IR "\fB\\$1\& \|\fI\\$2" "\\$3" "\\$4" "\\$5" "\\$6"
..
.de Qo
.RB \(oq "\\$1" "\(cq\\$2"
..
.de Qa
.BI "\fR\(oq\fB\\$1" " \\$2" " \\$3" " \\$4" "\fR\(cq\\$5"
..
.de Sp
.if n .sp
.if t .sp 0.4
..
.de Ix
.TP 25
\\$1
.nh
\\$2
.hy
..
.de Es
.Sp
.RS 5
.nf
..
.de Ee
.fi
.RE
.PP
..
.de Xs
.RS 5
.nf
..
.de Xe
.fi
.RE
..
.TH GIFSICLE 1 "11 July 2017" "Version \*V"
.SH NAME
gifsicle \- manipulates GIF images and animations
.SH SYNOPSIS
.B gifsicle
\%[options, frames, and filenames].\|.\|.
'
.SH DESCRIPTION
.B gifsicle
is a powerful command-line program for creating, editing, manipulating, and
getting information about GIF images and animations.
.PP
.B Gifsicle
normally processes input GIF files according to its command line
options and writes the result to the standard output. The
.Op \-i
option, for example, tells
.B gifsicle
to interlace its inputs:
.Es
\fBgifsicle \-i < pic.gif > interlaced-pic.gif\fR
.Ee
.PP
.B Gifsicle
is good at creating and manipulating GIF animations. By default, it
combines two or more input files into a \(lqflipbook\(rq animation:
.Es
\fBgifsicle pic1.gif pic2.gif pic3.gif > animation.gif\fR
.Ee
Use options like
.Op \-\-delay ", " \-\-loopcount ", and " \-\-optimize
to tune your animations.
.PP
To modify GIF files in place, use the
.Op \-\-batch
option. With
.Op \-\-batch ,
.B 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:
.Es
\fBgifsicle \-\-batch \-i *.gif
.Ee
.PP
New users may want to skip to
the Examples section at the end.
'
.SH CONCEPT INDEX
'
Concepts are on the left, relevant
.B gifsicle
options are on the right.
'
.Sp
.PD 0
.Ix "Animations, changing" "frame selections, frame changes, etc."
.Ix "\ \ \ disposal" "\fB\-\-disposal\fP"
.Ix "\ \ \ looping" "\fB\-\-loopcount\fP"
.Ix "\ \ \ portions of" "frame selections"
.Ix "\ \ \ smaller" "\fB\-\-optimize\fP, \fB\-\-colors\fP, \fB\-\-lossy\fP"
.Ix "\ \ \ speed" "\fB\-\-delay\fP"
.Ix "Bad output" "\fB\-\-careful\fP"
.Ix "Background color" "\fB\-\-background\fP"
.Ix "Colors, changing" "\fB\-\-change\-color\fP, \fB\-\-use\-colormap\fP, \fB\-\-dither\fP, \fB\-\-transform\-colormap\fP"
.Ix "\ \ \ reducing number" "\fB\-\-colors\fP, \fB\-\-dither\fP, \fB\-\-gamma\fP"
.Ix "Comments" "\fB\-\-comment\fP"
.Ix "Extensions" "\fB\-\-extension\fP, \fB\-\-app\-extension\fP, \fB\-\-extension\-info\fP"
.Ix "File size" "\fB\-\-optimize\fP, \fB\-\-unoptimize\fP, \fB\-\-colors\fP, \fB\-\-lossy\fP"
.TP 30
Image transformations
.Ix "\ \ \ cropping" "\fB\-\-crop\fP, \fB\-\-crop\-transparency\fP"
.Ix "\ \ \ flipping" "\fB\-\-flip\-*\fP"
.Ix "\ \ \ resizing" "\fB\-\-resize\fP, \fB\-\-scale\fP"
.Ix "\ \ \ rotating" "\fB\-\-rotate\-*\fP"
.Ix "Grayscale" "\fB\-\-use\-colormap\fP"
.Ix "Interlacing" "\fB\-\-interlace\fP"
.Ix "Positioning frames" "\fB\-\-position\fP"
.Ix "Screen, logical" "\fB\-\-logical\-screen\fP"
.Ix "Selecting frames" "frame selections (like \fB'#0'\fP)"
.Ix "Transparency" "\fB\-\-transparent\fP"
.Ix "Warnings" "\fB\-\-no\-warnings\fP"
.PD
'
.SH COMMAND LINE
.BR 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.
.PP
.B gifsicle
reads and processes GIF input files in order. If no GIF input file is
given, or you give the special filename \(oq\-\(cq,
it reads from the standard input.
.PP
.B gifsicle
exits with status 0 if there were no errors and status 1 otherwise.
'
.SH OPTIONS
Every option has a long form,
.Qo \-\-long\-descriptive\-name .
You don't need to type the whole long descriptive name, just enough to
make it unambiguous.
.PP
Some options also have a short form,
.Qo \-X .
You can combine short options if they don't take arguments:
.Qo \-IIb
is the same as
.Qo "\-I \-I \-b" .
But be careful with options that do take arguments:
.Qo \-cblah
means
.Qo "\-c \fRblah" ,
not
.Qo "\-c \-b \-l \-a \-h" .
.PP
Many options also have a converse,
.Qo \-\-no\-option ,
which turns off the option. You can turn off a short option
.Qo \-X
by saying
.Qo \+X
instead.
'
.\" -----------------------------------------------------------------
.SS Mode Options
Mode options tell
.B gifsicle
what kind of output to generate. There can be at most one, and it must
precede any GIF inputs.
.TP 5
.Op "\-\-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.
'
.TP
.Op \-\-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.)
'
.TP
.Op \-\-explode ", " \-e
'
Create an output GIF for each frame of each input file. The output GIFs are
named \(oqxxx.000\(cq, \(oqxxx.001\(cq, and so on, where \(oqxxx\(cq is the name of the input
file (or whatever you specified with
.Qo \-\-output )
and the numeric extension is the frame number.
'
.TP
.Op \-\-explode\-by\-name ", " \-E
'
Same as
.Op \-\-explode ","
but write any named frames to files \(oqxxx.\fIname\fR\(cq instead of
\(oqxxx.\fIframe-number\fR\(cq. Frames are named using the
.Qo \-\-name
option.
'
.\" -----------------------------------------------------------------
.SS General Options
General options control the information
.B gifsicle
prints and where it writes its output. The info options and
.Op \-\-verbose
can be turned off with
.Qo \-\-no\-X .
'
.Sp
.PD 0
.TP 5
.Op \-\-info ", " \-I
'
Print a human-readable description of each input GIF to the standard
output, or whatever file you specify with
.Op \-o .
This option suppresses normal output, and cannot be combined with mode
options like
.Op \-\-batch .
If you give two
.Op \-\-info
or
.Op \-I
options, however, information is printed to standard error, and normal
output takes place as usual.
'
.Sp
.TP 5
.Op \-\-color\-info ", " \-\-cinfo
'
Like
.Op \%\-\-info ,
but also print information about input files' colormaps.
'
.Sp
.TP 5
.Op \-\-extension\-info ", " \-\-xinfo
'
Like
.Op \%\-\-info ,
but also print any unrecognized GIF extensions in a
.BR hexdump (1)-like
format.
'
.Sp
.TP 5
.Op \-\-size\-info ", " \-\-sinfo
'
Like
.Op \%\-\-info ,
but also print information about compressed image sizes.
'
.Sp
.TP 5
.Op \-\-help ", " \-h
'
Print usage information and exit.
'
.Sp
.TP
.Oa \-o file
.TP
.Oa \-\-output file
'
Send output to
.IR file .
The special filename \(oq-\(cq means the standard output.
'
.Sp
.TP
.Op \-\-verbose ", " \-V
'
Print progress information (files read and written) to standard
error.
'
.Sp
.TP
.Op \-\-no\-warnings ", " \-w
'
Suppress all warning messages.
'
.Sp
.TP
.Op \-\-no\-ignore\-errors
'
Exit with status 1 when encountering a very erroneous GIF. Default is to
muddle on.
'
.Sp
.TP
.Op \-\-version
'
Print the version number and some short non-warranty information and exit.
'
.Sp
.PD 0
.TP 5
.Op \-\-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
.Op \-\-careful
option if you are having problems with a particular image.
'
.Sp
.TP
.Op \-\-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. Or
say
.Op \-\-no\-conserve\-memory .
'
.Sp
.TP
.Op \-\-nextfile
'
Allow input files to contain multiple concatenated GIF images. If a
filename appears multiple times on the command line, \fBgifsicle\fR 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 "\fBgifsicle
\-\-nextfile \-d10 \- \-d20 \- \-d30 \- > out.gif\fR" and write the three
GIF images, in sequence, to \fBgifsicle\fR's standard input.
'
.Sp
.TP
.Op \-\-multifile
'
Like
.Op \-\-nextfile ,
but read
.I 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 "\fBgifsicle
\-\-multifile \- > out.gif\fR" and write the GIF images, in sequence, to
\fBgifsicle\fR's standard input. Any frame selections apply only to the
last file in the concatenation.
'
.PD
'
.\" -----------------------------------------------------------------
.SS Frame Selections
A frame selection tells
.B 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.
.Sp
.PD 0
.TP 13
.BI # num
'
Select frame \fInum\fR. (The first frame is
.Qo #0 .
Negative numbers count backwards from the last frame, which is
.Qo #-1 .)
'
.TP 13
.BI # num1 \- num2
'
Select frames \fInum1\fR through \fInum2\fR.
'
.TP 13
.BI # num1 \-
'
Select frames \fInum1\fR through the last frame.
'
.TP 13
.BI # name
'
Select the frame named \fIname\fR.
.PD
.PP
The \(oq#\(cq character has special meaning for many shells, so you generally
need to quote it.
.PP
For example,
.Xs
\fBgifsicle happy.gif "#0"\fR
.Xe
uses the first frame from happy.gif;
.Xs
\fBgifsicle happy.gif "#0-2"\fR
.Xe
uses its first three frames; and
.Xs
\fBgifsicle happy.gif "#-1-0"\fR
.Xe
uses its frames in reverse order (starting from frame #-1\*Ethe
last frame\*Eand ending at frame #0\*Ethe first).
.PP
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.
'
.\" -----------------------------------------------------------------
.SS Frame Change Options
Frame change options insert new frames into an animation or replace or
delete frames that already exist. Some things\*Efor example, changing one
frame in an animation\*Eare difficult to express with frame selections, but
easy with frame changes.
'
.TP 5
.Oa \-\-delete frames " [" frames ".\|.\|.]"
'
Delete
.I frames
from the input GIF.
'
.TP
.Oa \-\-insert\-before "frame other-GIFs"
'
Insert
.I other-GIFs
before
.I frame
in the input GIF.
'
.TP
.Oa \-\-append "other-GIFs"
'
Append
.I other-GIFs
to the input GIF.
'
.TP
.Oa \-\-replace "frames other-GIFs"
'
Replace
.I frames
from the input GIF with
.IR other-GIFs .
'
.TP
\fB\-\-done\fR
'
Complete the current set of frame changes.
'
.PP
The
.I frames
arguments are frame selections (see above). These arguments always refer to
frames from the
.I original
input GIF. So, if \(oqa.gif\(cq has 3 frames and \(oqb.gif\(cq has one, this
command
.Xs
\fBgifsicle a.gif \-\-delete "#0" \-\-replace "#2" b.gif\fR
.Xe
will produce an output animation with 2 frames: \(oqa.gif\(cq frame 1, then
\(oqb.gif\(cq.
.PP
The
.I 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
.I other-GIFs
last until the next frame change option, so this command replaces the
first frame of \(oqin.gif\(cq with the merge of \(oqa.gif\(cq and \(oqb.gif\(cq:
.Xs
\fBgifsicle \-b in.gif \-\-replace "#0" a.gif b.gif\fR
.Xe
.PP
This command, however, replaces the first frame of \(oqin.gif\(cq with
\(oqa.gif\(cq and then processes \(oqb.gif\(cq separately:
.Xs
\fBgifsicle \-b in.gif \-\-replace "#0" a.gif \-\-done b.gif\fR
.Xe
.PP
Warning: You shouldn't use both frame selections and frame changes on
the same input GIF.
'
.\" -----------------------------------------------------------------
.SS Image Options
Image options modify input images\*Eby changing their interlacing,
transparency, and cropping, for example. Image options have three forms:
.Qo \-\-X ,
.Qo \-\-no\-X ,
and
.Qo \-\-same\-X .
The
.Qo \-\-X
form selects a value for the feature, the
.Qo \-\-no\-X
form turns off the feature, and the
.Qo \-\-same\-X
form means that the feature's value is copied from each input. The default
is always
.Qo \-\-same\-X .
For example,
.Op \-background= """#0000FF"""
sets the background color to blue,
.Op \-\-no\-background
turns the background color off (by setting it to 0), and
.Op \-\-same\-background
uses input images' existing background colors. You can give each option
multiple times; for example,
.Xs
\fBgifsicle \-b \-O2 \-i a.gif \-\-same\-interlace b.gif c.gif\fR
.Xe
will make \(oqa.gif\(cq interlaced, but leave \(oqb.gif\(cq and \(oqc.gif\(cq interlaced only
if they were already.
'
.Sp
.PD 0
.TP 5
.Oa \-B color
.TP
.Oa \-\-background color
'
Set the output GIF's background to
.IR color .
The argument can have the same forms as in the
.Op \-\-transparent
option below.
'
.Sp
.TP
.Oa \-\-crop x1 , y1 - x2\fR,\fIy2
.TP
.Oa \-\-crop x1 , y1 + width\fRx\fIheight
'
Crop the following input frames to a smaller rectangular area. The top-left
corner of this rectangle is
.RI ( x1 , y1 );
you can give either the lower-right corner,
.RI ( x2 , y2 ),
or the width and height of the rectangle. In the
.IR x1 , y1 + width x height
form,
.I width
and
.I 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,
.Op \-\-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.
'
.Sp
.TP
.Op \-\-crop\-transparency
'
Crop any transparent borders off the following input frames. This happens
after any cropping due to the
.Op \-\-crop
option. It works on the raw input images; for example, any transparency
options have not yet been applied.
'
.Sp
.TP
.Op \-\-flip\-horizontal
.TP
.Op \-\-flip\-vertical
'
Flip the following frames horizontally or vertically.
'
.Sp
.TP
.Op \-i
.TP
.Op \-\-interlace
'
Turn interlacing on.
'
.Sp
.TP
.Oa \-S width x height
.TP
.Oa \-\-logical\-screen width x height
'
Set the output logical screen to
.IR width x height .
.Op \-\-no\-logical\-screen
sets the output logical screen to the size of the largest output
frame, while
.Op \-\-same\-logical\-screen
sets the output logical screen to the largest input logical screen.
.Op \-\-screen
is a synonym for
.Op \-\-logical\-screen .
'
.Sp
.TP
.Oa \-p x\fR,\fIy
.TP
.Oa \-\-position x\fR,\fIy
'
Set the following frames' positions to
.RI ( x , y ).
.Op \-\-no\-position
means
.Op \-\-position " 0,0."
Normally,
.Oa \-\-position x\fR,\fIy
places every succeeding frame exactly at \fIx\fR,\fIy\fR. However, if an
entire animation is input, \fIx\fR,\fIy\fR is treated as the position for
the animation.
'
.Sp
.TP
.Op \-\-rotate\-90
.TP
.Op \-\-rotate\-180
.TP
.Op \-\-rotate\-270
'
Rotate the following frames by 90, 180, or 270 degrees.
.Op \-\-no\-rotate
turns off any rotation.
'
.Sp
.TP
.Oa \-t color
.TP
.Oa \-\-transparent color
'
Make
.I color
transparent in the following frames.
.I 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).
.PD
'
.\" -----------------------------------------------------------------
.SS Extension Options
Extension options add non-visual information to the output GIF. This
includes names, comments, and generic extensions.
'
.Sp
.PD 0
.TP 5
.Oa \-\-app\-extension app\-name " " extension
'
Add an application extension named
.I app\-name
and with the value
.I extension
to the output GIF.
.Op \-\-no\-app\-extensions
removes application extensions from the input images.
'
.Sp
.TP
.Oa \-c text
.TP
.Oa \-\-comment text
'
Add a comment,
.IR text ,
to the output GIF. The comment will be placed before the next frame in
the stream.
.Op \-\-no\-comments
removes comments from the input images.
'
.Sp
.TP
.Oa \-\-extension number " " extension
'
Add an extension numbered
.I number
and with the value
.I extension
to the output GIF.
.I Number
can be in decimal, octal, hex, or it can be a single character like \(oqn\(cq,
whose ASCII value is used.
.Op \-\-no\-extensions
(or
.Op +x )
removes extensions from the input images.
'
.Sp
.TP
.Oa \-n text
.TP
.Oa \-\-name text
'
Set the next frame's name to
.IR text .
This name is stored as an extension in the output GIF (extension number
0xCE, followed by the characters of the frame name).
.Op \-\-no\-names
removes name extensions from the input images.
'
.PD
'
.\" -----------------------------------------------------------------
.SS 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,
.Qo \-\-X ,
.Qo \-\-no\-X ,
and
.Qo \-\-same\-X ,
and you can give animation options multiple times; for example,
.Xs
\fBgifsicle \-b a.gif \-d50 "#0" "#1" \-d100 "#2" "#3"\fR
.Xe
sets the delays of frames 0 and 1 to 50, and frames 2 and 3 to 100.
'
.Sp
.PD 0
.TP 5
.Oa \-d time
.TP
.Oa \-\-delay time
'
Set the delay between frames to
.IR time
in hundredths of a second.
'
.Sp
.TP
.Oa \-D method
.TP
.Oa \-\-disposal method
'
Set the disposal method for the following frames to
.IR method .
A frame's disposal method determines how a viewer should remove the frame
when it's time to display the next.
.I Method
can be a number between 0 and 7 (although only 0 through 3 are
generally meaningful), or one of these names:
.BR none
(leave the frame visible for future frames to build upon),
.BR asis
(same as "none"),
.BR background " (or " bg ")"
(replace the frame with the background), or
.BR previous
(replace the frame with the area from the previous displayed frame).
.Op \-\-no\-disposal
means
.Op \-\-disposal = none .
'
.Sp
.TP
.Op \-l "[\fIcount\fR]"
.TP
.Op \-\-loopcount "[=\fIcount\fR]"
'
Set the Netscape loop extension to
.IR count .
.I Count
is an integer, or
.B forever
to loop endlessly. If you supply a
.Op \-\-loopcount
option without specifying
.IR count ,
Gifsicle will use
.BR forever .
.Op \-\-no\-loopcount
(the default) turns off looping.
.Sp
Set the loop count to one less than the number of times you want the
animation to run. An animation with
.Op \-\-no\-loopcount
will show every frame once;
.Op \-\-loopcount =1
will loop once, thus showing every frame twice; and so forth.
Note that
.Op \-\-loopcount =0
is equivalent to
.Op \-\-loopcount =forever,
not
.Op \-\-no\-loopcount .
'
.Sp
.TP
.Op \-O "[\fIlevel\fR]"
.TP
.Op \-\-optimize "[=\fIlevel\fR]"
'
Optimize output GIF animations for space.
.I Level
determines how much optimization is done; higher levels take longer, but
may have better results. There are currently three levels:
.Sp
.RS
.TP 5
.Op \-O1
Stores only the changed portion of each image. This is the default.
.TP 5
.Op \-O2
Also uses transparency to shrink the file further.
.TP 5
.Op \-O3
Try several optimization methods (usually slower, sometimes better results).
.Sp
.PP
Other optimization flags provide finer-grained control.
.Sp
.TP 5
.Op \-Okeep-empty
Preserve empty transparent frames (they are dropped by default).
.Sp
.PP
You may also be interested in other options for shrinking GIFs, such as
.Op \-k ,
.Op \-\-lossy ,
and
.Op \-\-no\-extensions .
.RE
'
.Sp
.TP 5
.Oa \-U
.TP
.Oa \-\-unoptimize
'
Unoptimize GIF animations into an easy-to-edit form.
.Sp
GIF animations are often optimized (see
.Op \-\-optimize )
to make them smaller and faster to load, which unfortunately makes them
difficult to edit.
.Op \-\-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.
.RE
'
.PD
'
.\" -----------------------------------------------------------------
.SS Image Transformation Options
'
Image transformation options apply to entire GIFs as they are read or
written. They can be turned off with
.Qo \-\-no\-option .
'
.Sp
.PD 0
.TP 5
.Oa \-\-resize width x height
'
Resize the output GIF to the given
.IR width " and " height .
If
.I width
or
.I height
is an underscore \(oq_\(cq, that dimension is chosen so that the
aspect ratio remains unchanged.
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
.Op \-\-no\-logical\-screen
(or
.Op +S )
to reset it so
.B gifsicle
uses image dimensions instead. See also
.Op \-\-resize\-method .
'
.Sp
.TP
.Oa \-\-resize\-width width
.TP
.Oa \-\-resize\-height height
'
Resize to a given width or height, preserving aspect ratio. Equivalent to
.Oa \-\-resize width x_
or
.Oa \-\-resize "" _x height .
'
.Sp
.TP
.Oa \-\-resize\-fit width x height
.TP
.Oa \-\-resize\-touch width x height
'
Resize the output GIF to fit within a rectangle with dimensions
.IR width x height .
The aspect ratio remains unchanged. The
.Op \-\-resize\-fit
option only shrinks the image\(emno resize is performed if the GIF already
fits within the rectangle. Either
.I width
or
.I height
may be an underscore \(oq_\(cq, which leaves that dimension unconstrained.
'
.Sp
.TP
.Oa \-\-resize\-fit\-width width
.TP
.Oa \-\-resize\-fit\-height height
.TP
.Oa \-\-resize\-touch\-width width
.TP
.Oa \-\-resize\-touch\-height height
'
Like
.Oa \-\-resize\-fit
and
.Op \-\-resize\-touch ,
but constrains only one dimension.
'
.Sp
.TP
.Oa \-\-scale Xfactor [x Yfactor ]
'
Scale the output GIF's width and height by
.IR Xfactor " and " Yfactor .
If
.I Yfactor
is not given, it defaults to
.IR Xfactor .
Scaling happens after all input frames have been combined and before
optimization.
'
.Sp
.TP
.Oa \-\-resize\-method method
'
Set the method used to resize images. The \(oqsample\(cq method runs
very quickly, but when shrinking images, it produces noisy results.
The \(oqmix\(cq method is somewhat slower, but produces better-looking
results. The default method is
currently \(oqmix\(cq.
.RS
.Sp
.PP
Details: The resize methods differ most when shrinking images. The
\(oqsample\(cq method is a point sampler: each pixel position in the
output image maps to exactly one pixel position in the input. 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 \(oqbox\(cq 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
\(oqmix\(cq method is a full bilinear interpolator. This is slower and
produces somewhat blurrier results, but avoids anomalies.
.Sp
.PP
Gifsicle also supports more complex resamplers, including
Catmull-Rom cubic resampling (\(oqcatrom\(cq), the Mitchell-Netravali
filter (\(oqmitchell\(cq), a 2-lobed Lanczos filter
(\(oqlanczos2\(cq), and a 3-lobed Lanczos filter (\(oqlanczos3\(cq).
These filters are slower still, but can give sharper, better results.
.RE
'
.Sp
.TP
.Oa \-\-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:
.Oa \-\-resize\-colors 64
allows Gifsicle to add intermediate colors for images that have fewer
than 64 input colors.
.PD
'
.\" -----------------------------------------------------------------
.SS Color Options
'
Color options apply to entire GIFs as they are read or
written. They can be turned off with
.Qo \-\-no\-option .
.Sp
.PD 0
.TP 5
.Oa \-k num
.TP