Generally disk space is cheap enough that doing these sorts of things aren't worth the extra complexity, especially when we just have to convert it back to png in order to serve it to the user at the end of the day.
LZMA is a more advanced compression algorithm than DEFLATE (which is what png uses), so its not entirely surprising it might give better results for some images. -- Bawolff On Tuesday 23 April 2024, TealSynapse--- via Wikitech-l < wikitech-l@lists.wikimedia.org> wrote: > > *i've never contributed to any mailing lists, or partaken much, so i don't > know how to start this off...* > > > *hi? i've realized i can compressed a dataset of lossless .png files down > to between a third- or a fourth of the initial size on disk. * > > > *that said: in compressing my own backups i find that lossless .png files > converted to .xpm (not .ppm, not .bmp) before being compressed result in a > compression that of 3- to 4 times smaller in size on disk than the initial > .png with it's own compression --- irregardless of any 'PNG optimization' > done beforehand: the resulting .xpm files remain identical in size and > compress to precisely the same size. * > > *the following commands¹ can surely be tinkered with to greater effect:* > > *---start of shell commands---* > mkdir -p xpm > magick convert image.png xpm/image.xpm > mkdwarfs -i xpm/ -o compressed.dfs -l9 > > *---end of shell commands---* > *now you have a compressed image, three to four times smaller in size on > disk, to inspect.* > > *here i openly wonder how a comparison - to assert whether the resulting > .xpm file and the lossless .png are indeed the same picture still - would > be carried out.* > > *likewise i see this quality of compression extends to the .xgm .xbm > formats.* > > > *in sharing i wish to bring up the above observation to my best ability. > insights welcome as to why this happens and if indeed the image resulting > from a lossless .png to .xpm conversion is the same - if this compressed > bitmap outperforms the PNG compression significantly without compromising > image integrity. (do reply with saying if this is irrelavant information > and or presented inadequately in any way: i don't wish to bring red > herrings to this mailing list.)* > > > *ultimately this is about if a large portion of WikiMedia imagedata indeed > can be compressed further by this process - in a 'Pareto improvement' kind > of way.* > > *-Ivy, 25* > > > > *for interest: sources to programs referenced and my brief notes on these.* > *[1]* > > *magick: https://imagemagick.org/index.php > <https://imagemagick.org/index.php>* > *mkdwarfs, part of the inappropriately named dwarfs toolset:* > > *https://github.com/mhx/dwarfs/blob/main/doc/mkdwarfs.md > <https://github.com/mhx/dwarfs/blob/main/doc/mkdwarfs.md>* > *note that the -l flag is given the option 9 in the command - this means > LZMA is used in this program.* > > *also note that while i use 'mkdwarfs' with LZMA here, i realize the same > result on any other program using LZMA or XZ occurs - like the following > 'dar', more adequate for single file extraction from an archive and > analyzing individual file compression values en masse. * > > *dar: http://dar.linux.free.fr/doc/man/dar.html > <http://dar.linux.free.fr/doc/man/dar.html>unfortunately the projects' > website doesn't use HTTPS, so a wayback machine link with HTTPS:* > > *https://web.archive.org/web/20240423233825/http://dar.linux.free.fr/doc/man/dar.html > <https://web.archive.org/web/20240423233825/http://dar.linux.free.fr/doc/man/dar.html>* > *---start of referenced dar command---* > dar -c output -zxz9 -R input/ > *---end of referenced dar command---* > > *lastly two clarifications:* > > *'a lossless .png file' here means an imagefile which never has been > converted in a lossy way. a .jpg file converted to a .png used in this > procedure produces an output taking more space on disk. * > > *'the procedure' here refers to conversion of a lossless .png to .xpm > imagefile format then compressed with either LZMA or XZ in any program.* > > > *thank you for reading.* >
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