Re: [hatari-devel] [patch] AVI recording PNG compression level

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On maanantai 10 marraskuu 2014, Nicolas Pomarède wrote:
> Le 09/11/2014 22:05, Eero Tamminen a écrit :
> > On sunnuntai 09 marraskuu 2014, Troed Sångberg wrote:
> >> JPG should only be used for photos with "natural content"
> >> PNG should be used for clipart, computer graphics etc
> >> 
> >> (The algorithms used by JPG assumes things about the content in the
> >> same way as MP3 assumes things about the nature of sound & ears)
> > 
> > Sure, but you can disable the lossy part and still get
> > some compression from cosine transformation & LZ.
> removing the quantization part and only keeping the DCT + RLE will IMO
> give poor results when not applied to rather "high" resolution images
> (ie : not 320x200 or 640x400) and/or photographic images.

I hadn't thought of the resolution.

> For emulator like images, where you often have strong transitions
> between color from one pixel to another, you will most likely get rather
> "blocky" results when you use lossy compression, and not very good
> compression ratio if you go lossless, as jpeg is more appropriate to
> region of pixels with transition between colors (hence the DCT usage)
> than to planar graphics where pixels have sometimes no relation to each
> other (especially on older machine like ST where you only add 7 level of
> intensity per color)

That's why I was thinking that it might be useful (only) for
Falcon hi-color mode.  Assumably such mode is chosen only when
more colors = smaller color transitions are used. :-)

	- Eero

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