Hi folks!
A while ago, someone raised the possibility of recompressing PNG files.
Unlike xz, this would save space not only on mirrors but also on live
installed systems. PNGs are nearly incompressible so this is mostly
independent from xz.
At least by number, there's a lot of PNG images:
zgrep -i '\.png ' Contents-*gz|wc -l
577815
zcat Contents-*gz|wc -l
4296965 (including 3*35 lines of header)
This massive number of files seems to be concentrated mostly in a limited
number of packages:
35276 widelands-data
28827 libjs-mathjax
22225 ns3-doc
19968 jsmath-fonts
13395 openclipart2-png
13296 freefoam-dev-doc
10271 w3-recs
9877 uqm-content
9643 wesnoth-1.11-data
9015 wesnoth-1.10-data
8120 openclipart-png
6773 oxygen-icon-theme
6546 lxde-icon-theme
6272 mixxx-data
5890 gnome-icon-theme
5068 triplea
4641 tuxfootball
4505 gnome-themes-extras
4180 gnome-colors-common
3780 lilypond-doc
Some time ago, I tested a number of png optimizers, and the best results, by
far, come from using "optipng -o4 -i0 -fix" then "advpng -z4". The former
attacks the payload well, then advpng (package advancecomp) has good deflate.
-o4 is there because higher optipng levels mess only with zlib arguments,
-i0 because advpng is afraid of interlaced files (why?), -fix because advpng
refuses to touch files with certain errors like cruft after the end, as
Adobe tools like to leave.
I did test the alternatives quite thoroughly, but the corpus I needed that
for was quite specific. It's possible some other set of tools might be
better in general; these settings are the highest for optipng+advpng that
make sense, though.
So here are the results:
size(MB) o o+a
widelands-data 105 95.1% 93.4%
libjs-mathjax 29 99.0% 98.5%
openclipart2-png 476 99.6% 99.4%
w3-recs 16 88.4% 84.2%
wesnoth-1.11-data 89 98.3% 98.1%
fonts-mathjax-extra 4 94.6% 90.0%
(sizes include .png images only, o is optipng, o+a optipng+advpng)
Nothing stunning, I'm not sure if savings of this kind are worth a lot of
heed. I'd probably be good to have a common tool somewhere, to not reinvent
the wheel for every package.
--
ᛊᚨᚾᛁᛏᚣ᛫ᛁᛊ᛫ᚠᛟᚱ᛫ᚦᛖ᛫ᚹᛖᚨᚲ
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