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recomp-jpg(1)               General Commands Manual              recomp-jpg(1)


NAME

       recomp-jpg - try to recompress JPEG image files that were saved at too
       high a quality level


SYNOPSIS

       recomp-jpg [-a(rithmetic)] [-h(elp)] [-t target_quality] [-q(uiet)]
       file...


DESCRIPTION

       recomp-jpg tries to recompress JPEG images that were initially saved at
       too high a quality level, to see if they can be made smaller.  This is
       accomplished using a combination of the filesize, cjpeg, djpeg,
       tempname, and opt-jpg utilities.


OPTIONS

       -a     Allow arithmetic coding to be used on re-written image files
              instead of the more standard Huffman coding.  This can yield
              image files that are 5-7% smaller, but older software (image
              viewers, web browsers, image editors) might not read them
              successfully.  USE WITH CAUTION.

       -d float
              Use the floating-point DCT method.  This is the most accurate
              and the default.

       -d int Use the standard integer DCT method.  This is less accurate but
              faster.

       -d fast
              Use the less accurate integer DCT method.  This is significantly
              less accurate but fastest.

       -h     Print help and quit.

       -t     Set the target quality value (on the IJG scale, between 0 and
              100) for the images.  The default value is 85.

       -q     Quiet output.  No output commentary will be printed.


EXAMPLES

       Recompress a couple of image files, to see if they can be made smaller:
              recomp-jpg image001.jpg image002.jpg

       Try recompressing all JPEG images in an entire directory tree:
              find . -name "*.jpg" -exec recomp-jpg {} \;

       Or alternatively, try recompressing all JPEG images this way:
              find . -name "*.jpg" -print0 | xargs -0 recomp-jpg

       Fully utilize a quad-core system while optimizing all JPEG images:
              find . -name "*.jpg" -print0 | xargs -0 -n 1 -P 4 recomp-jpg
              find . -name "*.jpg" | parallel recomp-jpg


NOTES

       Each image is recompressed to the target quality value.  If the
       recompressed version is smaller, it is kept.  If it is not smaller,
       then the recompressed version is discarded and the original remains
       unchanged.


CAVEATS

       This procedure is not "lossless", so use it with caution.  It is
       primarily intended for use with images that were originally saved with
       quality=90 or higher, where the file sizes can become much larger with
       little or no perceptible improvement in image quality.

       See http://www.faqs.org/faqs/jpeg-faq/ for more information about the
       effects of JPEG quality settings.


SEE ALSO

       filesize(1), cjpeg(1), djpeg(1), tempname(1), opt-jpg(1)


COPYRIGHT

       Copyright (C) 2006-2023 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                       2023 Mar 25                    recomp-jpg(1)

littleutils 1.2.6 - Generated Mon Jun 26 07:48:08 CDT 2023
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