A little experiment on compressint tile at saving time

[Cyrille Berger]

Hello,

I made a little experiment on saving for Krita, and instead of compressing the 
whole file, what happen if only the tiles are compressed.

For comparison point, I made a 5 layers 9000x9000 images with gradient in the 
Gimp:

* xcf : 85MB
* .kra with compressed tiles and no global compression: 67MB, saving time 1.6s
* .kra with uncompressed tiles and global compression: 28MB, saving time 28s
* .ora : 31MB

I do not have the time for .ora, but it was closed to 30s as well.

I also did experimentation with a multilayer image made with camera pictures:
* .kra with compressed tiles and no global compression: 88MB, saving time 2s
* .kra with uncompressed tiles and global compression: 56MB, saving time 20s

This is just for reference, we won't do any change for 2.2 on the way tiles 
are saved, but I think it is worth it for 2.3, and would warrant further 
investigation.

For the curious I have attached the (rough) patch I used for those 
measurements (you would also need to disable global compression in 
KoStoreZip).

-- 
Cyrille Berger
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