Re: YCbCr continued
Re: YCbCr continued
- Subject: Re: YCbCr continued
- From: Darrin Cardani <email@hidden>
- Date: Tue, 5 Aug 2008 09:15:59 -0700
On Aug 4, 2008, at 3:23 PM, Brad Wright wrote:
Hi Pro Apps Team:
Here's what I did. I created a core image filter that generates a
color that fills the entire screen. All this filter does is display
what ever values you feed into it for the vec4 color that is
returned (pre-multiplied of course). I then used the built in Final
Cut Scopes to read the color values back. It appears that the color
neutral point is when both U and V are at 0.42 - 0.44 depending on
the value for Y. At least that's what the Final Cut Scopes are
saying. I looked at both the RGB parade and the Vectorscope to
verify that these values line up. I'm apply this filter directly
over a video frame from an FxTexture mapped into a CIImage. I've
been through the documentation and I can't figure out how Final Cut
is mapping these values. The U and V values should stay color
neutral while the Y value varies up or down. I'm not seeing that
happening. It appears the Hue is being shifted around as the Y
varies. I'm not sure how the U and V values arrive at between 0.42
and 0.44.
The best I can figure is that Cb and Cr are mapped at between 0 -
224 without the offset that the documentation says there is.
If I assume that the color neutral point is .42-0.44 in float point,
then I can get this value by mapping:
Zero Saturation point 112
Maximum Cb and Cr value of 255
112/255 = .43921569
approximately .439
Does anyone know why this would happen?
Brad,
Is it possible that you're not setting up Core Image's color space
correctly? What happens when you try the same thing in a straight
OpenGL ARB Fragment program with no Core Image involved? Do you see
the same problems?
Darrin
--
Darrin Cardani
email@hidden
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