opt-png(1) General Commands Manual opt-png(1)
NAME
opt-png - losslessly optimize PNG image files
SYNOPSIS
opt-png [-h(elp)] [-f filelist] [-g(ray)] [-q(uiet)] [-p(ipe)]
[-r(es) DPI] [-t(ouch)] [-T threads] file...
DESCRIPTION
opt-png losslessly optimizes PNG images by removing unused palette
entries and/or optimizing the filtering algorithm. This is
accomplished using a combination of the optipng, pngcrush, pngrecolor,
and pngstrip utilities.
OPTIONS
-h Print help and quit.
-f file_list
Read the names of files to be processed from the specified file.
-g Force output to grayscale.
-p Read the names of files to be processed from stdin.
-q Quiet output. No output commentary will be printed.
-r DPI Write the specified resolution into the pHYs chunk of the output
file. Units are in pixels-per-inch. To convert from pixels-
per-meter, multiply by 0.0254 (or divide by 39.37). Note that
this does not change the number of pixels in the image. It only
changes the assumed size of the pixels.
-t Preserve timestamp on modified files.
-T threads
Process up to the specified number of files in parallel. The
default value is half the multi-threading capability of the CPU,
i.e., half the sibling count as listed in /proc/cpuinfo.
EXAMPLES
Optimize a couple of image files:
opt-png image001.png image002.png
Optimize all PNG images in an directory tree, utilizing half of all
cores: find . -name "*.png"| opt-png -p
Fully utilize a quad-core system while optimizing all PNG images:
find . -name "*.png" -print | opt-png -p -T 4
NOTES
If at all possible, make sure that pngcrush version 1.6.x or later is
running on your computer. It performs substantially better than
pngcrush 1.5.10 (and earlier) on black-and-white (and other low-color)
images due to use of the Z_RLE zlib strategy.
If opt-png appears to be malfunctioning, try running it in single-
threaded mode by using the -T 1 option. This permits more meaningful
error messages to be printed.
SEE ALSO
optipng(1), pngcrush(1), pngrecolor(1), pngstrip(1)
COPYRIGHT
Copyright (C) 2004-2026 by Brian Lindholm. This program is free
software; you can use it, redistribute it, and/or modify it under the
terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
littleutils 2026 Jan 01 opt-png(1)
littleutils 1.4.0 - Generated Wed Feb 18 07:37:52 CST 2026