And there is all the metadata that tends to get jumbled/warped/damaged/lost. That is another risk that has to be taken into account when processing originals to be stored in another format.
DJ On Wed, Apr 24, 2024 at 3:28 AM Dmitry Brant <dbr...@wikimedia.org> wrote: > It is true that the PNG format doesn't offer the absolute best compression > - no one would claim it does. What it does offer is ultimate compatibility > -- it's viewable on nearly every browser and device ever made, which is > more important than disk usage. > > When ImageMagick converts from PNG to XPM, the image remains "the same", > but it changes the image from an RGB encoding to a palette-based bitmap > with a predefined set of colors. Combine this with modern compression, and > you should indeed see a better compression ratio. > > > On Tue, Apr 23, 2024 at 8:30 PM 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.* >> _______________________________________________ >> Wikitech-l mailing list -- wikitech-l@lists.wikimedia.org >> To unsubscribe send an email to wikitech-l-le...@lists.wikimedia.org >> >> https://lists.wikimedia.org/postorius/lists/wikitech-l.lists.wikimedia.org/ > > > > -- > Dmitry Brant > Lead Software Engineer (Android) > Wikimedia Foundation > https://www.mediawiki.org/wiki/Wikimedia_mobile_engineering > > _______________________________________________ > Wikitech-l mailing list -- wikitech-l@lists.wikimedia.org > To unsubscribe send an email to wikitech-l-le...@lists.wikimedia.org > https://lists.wikimedia.org/postorius/lists/wikitech-l.lists.wikimedia.org/
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