Re: optimizing PNGs
I think it's worth approaching upstream and recompressing the images in upstream.
Ondřej Surý
On 26. 5. 2013, at 17:56, Adam Borowski <kilobyte@angband.pl> wrote:
> 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.
>
> --
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>
>
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