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Re: [ITS]RE: i/ Luma coefficients for DTV



At 8:55 PM -0400 8/4/98, ParkSeward at aol.com wrote:
>In a message dated 8/3/98 8:02:21 PM, petemo at microsoft.com wrote:
>
><<Coincidentally I just saw an ad for a 10 bit "linear" RGB scanner
>advertising 1.07 billion colors!
>>>
>
>Correct me if I'm wrong, but if I have a TV that is 480x640 pixels, I can only
>see 307,200 colors at any one time because that's all the pixels I have. Yes,
>the next frame can show me different colors, but at any one time, I can only
>see a little over 300,000 colors. True?
>
>-Park

Not true. There is insufficient time for your visual system to capture even
this number of samples in moving imagery. What our visual system is
optimized for is the detection of edge information (how we distinguish
shapes and objects) and small differences in luma and color (how we
distinguish details from images that look much the same). For example, it
is very helpful to see the lion hiding in the bushes under the tree where
the differences in brightness levels and colors are quite small.

This issue is, in fact, related to one of the largest problems we have with
digital video compression. It does just fine with random dithered imagery
with lot's of edge information--quantization replaces detail with noise,
but we don't have time to process the detail when the images are updated at
60 fields/frames per second). Where it falls down is the quantization of
the small differences in naturally occuring imagery (the sky or water) and
synthetic imagery (smooth gradients).

As for the number of colors, or shades of grey, avialable, it is important
to distinguish between that artists palette and the painting. More values
make it possible to improve the dynamic range and colorimetry that can be
represented by the system.





Regards
Craig Birkmaier
Pcube Labs

The best way to predict the future is to invent it -- Alan Kay





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