On Wed, 6 Jul 2005, Matto Marjanovic wrote:

> One thing though:  in the frame you sent me, about 10% of the pixels
>  are clipped in the initial conversion to R'G'B' --- these are Y'CbCr
>  values in the orginal frame which lie outside of the R'G'B' color
>  cube.  When they are clipped (projected/forced into the R'G'B' cube),
>  they will generally appear brighter (the Y' of the clipped pixel will
>  be higher than the original Y' value).

        The reverse also be, possibly, a problem?  When going from R'G'B'
        to broadcast range Y'CbCr the clip/core to 16-235 and 16-240 can
        cause luma dimming and color shifts (saturated red is particularily
        nasty to deal with).

>  be no visible transition between the frames with 'effects' and those
>  without?  Or doing the work in Y'CbCr colorspace [all non-ideal for
>  a few reasons].  Or writing tools which will handle negative R'G'B'

        Hmmm, that's not what I've found to be the case.  Can you elaborate
        on why doing all the work in Y'CbCr is non-ideal?  So far I've found
        doing the rendering/filtering/compositing/etc work in Y'CbCr format 
        (with 10bit per sample data the math in done with 32bit floating point)
        gives fantasically good results.

        Cheers,
        Steven Schultz



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