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Optimizing PNG tiles

Posted by adaviel on 11 August 2009 in English.

I stumbled across optipng (for Linux) recently, and wondered whether it would be worth running this on the OSM tiles (or rather, incorporating the algorithm into newly generated ones).

It seems to get maybe 25% size reduction on "empty" tiles (ocean, fields) but only 2-3% on "busy" urban tiles.

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Discussion

په 11 August 2009 په 00:18 باندې د andrewpmk تبصره

It would probably take far too much CPU power to be worth running on the tile server.

په 11 August 2009 په 00:51 باندې د Falcorian تبصره

And of course optipng isn't the only compression program, pngout for example generally gets smaller files at the cost of more processing time.

په 11 August 2009 په 01:03 باندې د adaviel تبصره

I remember I used to get significant reduction in GIFs by reducing the palette size, before everyone had broadband. With people getting images over cell data networks (and maybe paying per kb) there may be some point to it again.

On a related topic, I forget whether I saw it on OSM or Maemo Mapper - is there any scheme to save downloads by redirecting all requests for "empty blue tile" to the same URL ?

په 14 August 2009 په 08:56 باندې د Firefishy تبصره

The OSM Mapnik tiles are 256 colour PNGs to improve their size.
The tile server is CPU bound and currently bandwidth usage is not a problem.

په 15 August 2009 په 03:18 باندې د adaviel تبصره

I tried pngout. Much slower than optipng, at least on the maybe 1.5Mpixel image I used.
I was thinking about bandwidth on mobile clients, not the server.

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