A Standard for Thumbnailers

Benedikt Meurer benny at xfce.org
Wed Jan 10 07:23:17 PST 2007

Erlend Davidson wrote:
>>  it makes use of the fact that JPEG's are DCT's
>> and you get "free" downscaling on decode by factors of 2, 4 and 8
>> times in each
>> dimension simply by decoding the DCT at a different output res (and
>> throwing
>> out higher frequency DCT elements). it means for an incredibly faster
>> decode
>> and thus thumbnail generation is sped up massively. you speed up the
>> other half
>> of this work by using JPEG output for thumbnails. it makes a
>> difference. a
>> perceptible and measurable one. people notice.
> Could a similar optimisation be applied to PNG to generate those
> thumbnails very quickly?

BTW. both Thunar and Nautilus use the same trick with libjpeg, so that
won't save time anyway. Saving to JPEG won't boost performance either.
What's however interesting is the saved disk space.


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