Re: What color transformation formula are you using in FCP for Y Pb Pr ?
Re: What color transformation formula are you using in FCP for Y Pb Pr ?
- Subject: Re: What color transformation formula are you using in FCP for Y Pb Pr ?
- From: Paul Schneider <email@hidden>
- Date: Mon, 4 Aug 2008 11:02:50 -0500
Hi Brad,
Our YCbCr images are in R408 format (or r4fl for floating point). If
you're accessing the 8-bit images from a CI kernel (or other fragment
shader), the 0-255 values will be scaled to 0-1. In R408, the white
point is at Y = 235, so I would expect white to be at (235 / 255) from
the perspective of your CI kernel.
As mentioned in the FxImage.h header, the documentation for our YCbCr
format, along with conversion matrices, can be found here:
http://developer.apple.com/quicktime/icefloe/dispatch027.html
Hope that helps,
- Paul
On Aug 4, 2008, at 12:23 AM, Brad Wright wrote:
Hi Pro Apps:
I'm trying to convert the Final Cut YUV into floating point RGB and
then back to Final Cut YUV. I'm doing this in Core Image using a
custom CIFilter kernel. So far, I'm stumped on how Final Cut is
converting the raw image data into FxTextures. The values in the
Texture don't match Y Pb Pr floating point. I've found that the
value of white lies somewhere between Cb and Cr equaling 0.42 to
0.44 depending on the value of Y. How are 8 bit Y Cb Cr values
getting mapped into FxTextures? Is it converted from Y Pb Pr values
of +112 to -112 for Cb and Cr to some floating point value? I can't
find any documentation on the mapping to and from YUV to RGB
Brad Wright
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