Ubuntu Manpage: gif2png - convert GIFs to PNGs

NAME

       gif2png - convert GIFs to PNGs

SYNOPSIS

       gif2png [-bdfghinprsvwO] [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 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.

-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.

-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. 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.

PROBLEMS

       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.

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 <http://www.libpng.org/pub/png/> has very complete information on the
       PNG standard, PNG libraries, and PNG tools.

AUTHORS