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PC-FX RGB to YUV conversion?

 
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cdoty
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Joined: 02 Feb 2005
Posts: 73
Location: Houston, TX
PostPosted: Sun Jul 25, 2010 9:17 pm    Post subject: PC-FX RGB to YUV conversion? Reply with quote
What is the exact conversion from RGB to YUV used on the PC-FX?

I've tried the YUV - RGB Color Format Conversion from http://www.equasys.de/colorconversion.html (with the U/V scaled to 4 bit). It's pretty close, except the that Y and the green are a bit high.

I initially attempted some of the other values, but the green was way off. I though it was an error in my code until I noticed Hage (http://homepage1.nifty.com/hyperclub/download/Alpha/index.html) did the same thing.
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dmichel
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Joined: 04 Apr 2002
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PostPosted: Mon Jul 26, 2010 1:17 pm    Post subject: Reply with quote
Good question!

For patching some images of Pia Carrot I needed a RGB to YUV converter too, I tried many formulas but none of them was exact, there was always a little glitch, so in the end I used a brute force method.

I simply used the YUV to RGB converter over the whole range of possible YUV values to fill a RGB array, something like that :

Code:
for(i = 0; i <= 0xFFFF; i++) {
   data = YUV_to_RGB(i);
   rgb[i][0] = data >> 16;
   rgb[i][1] = data >> 8;
   rgb[i][2] = data;
}


And then to convert a RGB value to YUV I was simply searching for the closest match in the RGB array to get the corresponding YUV value. It's a bit slow and memory hungry though, if you need it for some real-time calculation on the PCFX this probably won't work, but for batch conversion of some images that did the trick for me.
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