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.
-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.
-t
Change behavior of web-probe (-w) mode to accept GIFs with
transparency.
-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 or
transparency 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. The problem is not with PNG itself or
with gif2png, but with the poor-to-nonexistent support for PNG
transparency and animation in most browsers.
The web-probe switch is intended to be used with scripts for converting
web sites. All PNGs generated from the pathnames it returns will be
properly rendered in Netscape Navigator 4.04+, Internet Explorer
versions 4.0b1+, and all other current web browsers. Note: in future
releases of gif2png, the meaning of this switch may change to reflect
the capabilities of prevalent browsers.
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.
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
Eric S. Raymond <esr@thyrsus.com>, 1999.