See also [[ImageProcessing]].

== JPEG ==

[[http://jpegclub.org/jpegtran/|jpegtran]] (part of libjpeg-progs in Debian) can losslessly optimize JPEG files:

{{{#!highlight sh numbers=off
parallel -u 'echo {}; jpegtran -optimize -progressive -perfect -copy all -outfile {}.tran {} && mv {}.tran {}' ::: *.jpg
}}}

Source: [[http://schnouki.net/2011/07/22/optimizing-jpeg-pictures/|/dev/schnouki - Optimizing JPEG pictures]]

Another interesting tool is [[http://www.kokkonen.net/tjko/projects.html|jpegoptim]] ([[http://freshmeat.net/projects/jpegoptim/|jpegoptim on freshmeat]]):

{{{#!highlight sh numbers=off
parallel jpegoptim ::: *.jpg
}}}

though the compression does not appear to be as good, and it's known to wipe JPEG metadata even when told not to.

Other useful stuff:

{{{#!highlight sh numbers=off
# mozjpeg
parallel -u 'echo {}; cjpeg -outfile {}.mozjpeg -optimise -progressive -quality 90 {} && mv {}.mozjpeg {}' ::: *.jpg
# 4:2:0 chroma subsambling
parallel -u 'echo {}; convert {} -sampling-factor "2x2,1x1,1x1" {}.422 && mv {}.422 {}' ::: *.jpg
}}}

== PNG ==

=== 256 color (8-bit) ===

Converting to 8-bit PNG (maximum of 256 colors) saves a significant amount of space, though this should be done BEFORE other optimization:

{{{#!highlight sh numbers=off
find . -name '*png' -print0 | xargs -0 -n64 -P$(nproc) pngnq -e .8 -n 256
find . -name '*.8' -exec echo mv '{}' '{}'.png \; | sed 's/\.8\./\./'
}}}

To take advantage of OS file caching, 8-bit conversion and PNG optimization can be wrapped into a script, optimize-png-8bit:

{{{#!highlight sh
#!/bin/sh
for i in "$@"; do
        pngnq -e .png.8 -n 256 $i
        mv $i.8 $i
done
optipng -quiet -o3 $@
advpng -z -4 $@
advdef -z -4 $@
}}}

which you can run in parallel with:

{{{#!highlight sh numbers=off
find . -name '*png' -print0 | xargs -0 -n64 -P$(nproc) optimize-png-8bit
}}}


=== Full color ===

{{{#!highlight sh numbers=off
find . -name '*png' -print0 | xargs -0 -n64 -P$(nproc) optipng -o3
find . -name '*png' -print0 | xargs -0 -n64 -P$(nproc) advpng -z -4
find . -name '*png' -print0 | xargs -0 -n64 -P$(nproc) advdef -z -4

# Or
parallel -n 64 -u 'optipng -o3 {}; advpng -z -4 {}; advdef -z -4 {}' ::: *png
}}}

To take advantage of OS file caching, PNG optimization can be wrapped into a script, optimize-png:

{{{#!highlight sh
#!/bin/sh
optipng -quiet -o3 $@
advpng -z -4 $@
advdef -z -4 $@
}}}

which you can run in parallel with:

{{{#!highlight sh numbers=off
find . -name '*png' -print0 | xargs -0 -n64 -P$(nproc) optimize-png
}}}

pngcrush is another tool that unfortunately does not work as well as the above, but can be run in parallel with:

{{{#!highlight sh numbers=off
parallel -u 'echo {}; pngcrush -reduce -brute {} {}.pngcrush && mv {}.pngcrush {}' ::: *.png
# Remove color space information
parallel -u 'echo {}; pngcrush -reduce -brute -rem gAMA -rem cHRM -rem iCCP -rem sRGB {} {}.pngcrush && mv {}.pngcrush {}' ::: *.png
}}}

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CategoryCheatSheet