[vorbis-dev] ogg pic format (again).. here's why

[Chris Hanson]

At 6:41 PM +0100 1/26/01, Gerry wrote:
>Both pictures, animations and
>"real" movies (should) have this in common: compress it to as good quality
>and small size as possible. Why not make all in one ?

Except, of course, that they have very different perceptual and 
temporal characteristics.

For instance, the Discrete Cosine Transform used in JPEG and MPEG can 
result in lots of visual noise in large single-color areas.  Most 
animation consists of a large number of large single-color areas. 
Hence a compression scheme built around a DCT isn't the best for 
animation.

Similarly, computer images will generally either be in an RGB or CMYK 
color space (depending on how they were generated/acquired and where 
they're eventually destined to be displayed).  Video, on the other 
hand, is usually both captured and displayed in a 
luminance/chromanance format (often 4:2:2 Y'Cb'Cr').  These three 
color spaces have very different gamuts and perceptual behaviors. 
(For instance, with color printing -- CMYK, aka "process colors" or 
subtractive primaries -- you also have to worry about halftone 
patterns and dot gain.)

   -- Chris


-- 
Chris Hanson <cmh at bDistributed.com>
bDistributed.com: Making Business Distributed

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