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

[Nicolas Pomarède <npomarede@xxxxxxxxxxxx>]

Le 09/11/2014 22:05, Eero Tamminen a écrit :
> Hi,
>
> 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.

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)