Mac OS X

Gildas Bazin gbazin at
Sat Aug 4 22:55:37 CEST 2001

On Saturday 04 August 2001 7:00 pm, Florian G. Pflug wrote:
> On Sat, Aug 04, 2001 at 06:23:51AM +0100, Gildas Bazin wrote:
> > You are talking about yuv->rgb conversion... Can't you use YUV overlay on 
> > MacosX? this way the conversion would be done in hardware.
> Hi
> sorry for answering twice...
> Where can I find detailed information about YUV-formats?

You should find all the information you need here:

> addidiontally, when storing images in YUV, you can ommit e.g. the u & v
> information for every second line, since the human eye has a lower
> "resolution" regarding differences in color than it has regarding
> differences in brightness.

Most MPEG2 videos are already encoded in YCbCr 4:2:0, which means that Cb and 
Cr are subsampled by 2 both in horizontal and vertical directions compared to 
the Y picture.

> I am wondering, if gamma-correction (which can be applied to images with
> macosx - at least when using quickdraw) couldn't be used for some "pseudo
> yuv rendering"

Hmm, I don't think it's possible because Cb and Cr samples (or U and V if you 
prefer) don't contain that much information. They contain "difference" 
information, because usually in an RGB picture, the R, G and B components 
have a lot information in common. So it's more efficient to encode this 
picture into a black and white version, plus the chroma difference.
( I know it's not well explained but if you read the document I pointed you 
to, you will understand ;-)


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