Ubuntu Manpage: gif2png - convert GIFs to PNGs

Provided by: gif2png_2.5.8-1build1_amd64

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