GIF2PNG(1) gif2png GIF2PNG(1)
Graphics Graphics
06/20/2019
NAME
gif2png - convert GIFs to PNGs
SYNOPSIS
gif2png [-bdfghimnprsvwO] [file.[gif]...]
DESCRIPTION
The gif2png program converts files in the obsolescent Graphic
Interchange Format (GIF) to Portable Network Graphics (PNG) format, an
open W3C standard.
Normally gif2png converts each file named on the command line, leaving
the original in place. If a name does not have a .gif extension, the
unmodified name will be tried first, followed by the name with .gif
appended. For each file named foo.gif, a foo.png will be created.
When a multi-image GIF file named foo.gif is converted, gif2png
creates multiple PNG files, each containing one frame; their names
will be foo.png, foo.p01, foo.p02 etc.
If no source files are specified and stdin is a terminal, gif2png
lists a usage summary and version information, then exits.
If no source files are specified, and stdin is a device or pipe, stdin
is converted to noname.png. (The program can't be a normal
stdin-to-stdout filter because of the possibility that the input GIF
might have multiple images).
However, if filter mode is forced (with -f) stdin will be converted to
stdout, with gif2png returning an error code if the GIF is
multi-image.
The program will preserve the information contained in a GIF file as
closely as possible, including GIF comment and application-data
extension blocks. All graphics data (pixels, RGB color tables) will be
converted without loss of information. Transparency is also preserved.
There is one exception; GIF plain-text extensions are skipped.
The program automatically converts interlaced GIFs to interlaced PNGs.
It detects images in which all colors are gray (equal R, G, and B
values) and converts such images to PNG grayscale. Other images are
converted to use the PNG palette type. Duplicate color entries are
silently preserved. Unused color-table entries cause an error message.
The action of the program can be modified with the following
command-line switches:
-b {#}RRGGBB
Background. Replace transparent pixels with given RGB value, six
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GIF2PNG(1) gif2png GIF2PNG(1)
Graphics Graphics
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hexadecimal digits interpreted as two hexits each of red, green,
and blue value. The value may optionally be led with a #,
HTML-style.
-d
Delete source GIF files after successful conversion.
-f
Filter mode. Convert GIF on stdin to PNG on stdout, return error
if the GIF is multi-image.
-m
Preserve file modification time. The PNG output gets the mod time
of the input file, not the time it was converted.
-g
Write gamma=1/2.2 and sRGB chunks in the PNG.
-h
Generate PNG color-frequency histogram chunks into converted color
files.
-i
Force conversion to interlaced PNG files.
-n
Force conversion to non-interlaced PNG files.
-p
Display progress of PNG writing.
-r
Try to recover data from corrupted GIF files.
The recovery algorithm enabled by -r is as follows: Unused color
table entries will not trigger an error message as they normally
do, but will still be preserved unless -O is also on, in which
case they will be discarded. Missing color tables will be patched
with a default that puts black at index 0, white at index 1, and
supplies red, green, blue, yellow, purple and cyan as the
remaining color values. Missing image pixels will be set to 0.
Unrecognized or corrupted extensions will be discarded.
-s
Do not translate the GIF Software chunk to a PNG annotation.
-v
Verbose mode; show summary line, -vv enables conversion-statistics
and debugging messages.
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GIF2PNG(1) gif2png GIF2PNG(1)
Graphics Graphics
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-w
Web-probe switch; list GIFs that do not have multiple images to
stdout. GIFs that fail this filter cause error messages to stderr.
-O
Optimize; remove unused color-table entries. Normally these
trigger an error message and disable -d (but conversion is
completed anyway). Also, use zlib compression level 9 (best
compression) instead of the default level.
LIMITATIONS
A sufficiently malformed GIF can confuse this program seriously enough
to segfault it. If this happens while processing multiple GIFs,
conversion of the batch will be interrupted.
Naively converting all your GIFs at one go with gif2png is not likely
to give you the results you want. Animated GIFs cannot be translated
to PNG, which is a single-image format.
The web-probe switch is intended to be used with scripts for
converting web sites. In versions of this tool up to 2.5.2 it filtered
out GIFs with transparency as well as GIFs with animations, but
support for PNG transparency has been universal in browsers since
about 2006.
RETURN VALUES
Normally returns 0 for successful comp[letion. A return of 1 is a
recoverable error (batch processing continues), A return of 2 is an
unrecoverable error.
STANDARDS AND SPECIFICATIONS
Copies of the GIF89 specification are widely available on the Web;
search for "GRAPHICS INTERCHANGE FORMAT". The Graphics Interchange
Format(c) is the Copyright property of CompuServe Incorporated.
GIF(sm) is a Service Mark property of CompuServe Incorporated. The GIF
format was formerly covered by a blocking patent on LZW compression,
but it expired in June 2003.
The PNG home site at <m[blue]http://www.libpng.org/pub/png/m[]> has
very complete information on the PNG standard, PNG libraries, and PNG
tools.
SEE ALSO
web2png(1)
AUTHORS
Code by Alexander Lehmann <alex@hal.rhein-main.de>, 1995.
Auto-interlace conversion and tRNS optimization by Greg Roelofs
<newt@pobox.com>, 1999. Man page, -O, -w, and production packaging by
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GIF2PNG(1) gif2png GIF2PNG(1)
Graphics Graphics
06/20/2019
Eric S. Raymond <esr@thyrsus.com>, 1999. -m option by Steve Ward,
2012.
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