opt-jpg(1) General Commands Manual opt-jpg(1)
NAME
opt-jpg - losslessly optimize JPEG image files
SYNOPSIS
opt-jpg [-h(elp)] [-a(rithmetic)] [-d DCT_arithmetic] [-f filelist]
[-g(ray)] [-m markers_to_copy] [-M maximum_quality] [-p(ipe)]
[-q(uiet)] [-r rotation_angle] [-t(ouch)] [-T threads] file...
DESCRIPTION
opt-jpg losslessly optimizes JPEG images. This is accomplished using a
combination of the cpeg, dpeg, imagsize, and jpegtran utilities.
OPTIONS
-h Print help and quit.
-a Allow arithmetic coding to be used on re-written image files
instead of the more prevalent Huffman coding. This can yield
image files that are 5-7% smaller, but older programs (image
viewers, web browsers, image editors) might not read them
successfully. USE WITH CAUTION.
-d DCT_arithmetic
Specify the type of DCT arithmetic to use. The choices are
"float" (the default), "int" (less accurate but a little
faster), and "fast" (not recommended). See cjpeg(1) for more
details. This option only applies when the -M option is used.
-f file_list
Read the names of files to be processed from the specified file.
-g Force the output to grayscale. [Note: This operation is not
lossless.]
-m markers_to_copy
Which markers to copy from the source file. The choices are
"none" (the default), "comments", "icc", and "all". See
jpegtran(1) for more details. This option is set to "none" when
the -M option is used.
-M maximum_quality
Set the maximum permissible quality value (on the IJG scale,
between 0 and 100) for the images. [Note: This operation is not
lossless.]
-p Read the names of files to be processed from stdin.
-q Quiet output. No output commentary will be printed.
-r rotation_angle
Rotate the image by 90, 180, or 270 degrees. Identical to the
"-rotate" option from jpegtran. [Note: This operation is not
always lossless.]
-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, forcing a conversion to grayscale:
opt-jpg g image001.jpg image002.jpg
Optimize all JPEG images in an directory tree, utilizing half of all
cores: find . -name "*.jpg" -print | opt-jpg -p
Fully utilize a quad-core system while optimizing all JPEG images:
find . -name "*.jpg" -print | opt-jpg -p -T 4
NOTES
This program may create progressive JPEG files from images that were
previously non-progressive. Curiously, they are sometimes smaller.
The -M and -r options cannot be used simultanously. If both rotation
and image quality limits must be imposed, first rotate the images using
rot-jpg with the -F (fast) option, then recompress with opt-jpg with
the -M option.
If opt-jpg appears to be malfunctioning, try running it in single-
threaded mode using the -T 1 option. This permits more meaningful
error messages to be printed.
SEE ALSO
cjpeg(1), djpeg(1), imagsize, jpegtran(1), rot-jpg(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-jpg(1)
littleutils 1.4.0 - Generated Wed Feb 18 07:28:58 CST 2026