Doom9's Forum - View Single Post - color adjust necessary in capture->SVCD?

trevlac · 19th February 2004, 05:53

@Kika

This thread got me re-interested in the whole YUV to RGB conversion thing. So I made an avisynth plugin to convert from YUY2 to RGB without changing the range. Basically, I followed Poynton's formulas for studio RGB. The plugin is here. The function is YUY2toRGB219(interpolate=true). Default for interpolation is false. It just does an average across the 2 closest pixels for every other pixel.

I did a bunch of testing and here are my basic findings:

- YUY2 contains about 25% of the colors available in RGB255
- The remapping that occurs for a normal RGB255->YUV235 changes the colors(not by much)
- Converting from RGB->YUV without remapping again changes the colors due to the limits of 8 bit YUV storage
- If you go RGB->10 bit YUV and limited remapping, it appears you do not change the colors

- Going from YUV->RGB219 and not remapping appears to NOT change the colors. RGB is a big enough space and efficiently uses the 8 bits, so there does not appear to be loss.
- Going from YUV->RGB255 can truncate data out of the nominal range. I did not test to see if the remapping looses anything.

So... the good news appears to be that if you start with YUV, going to RGB219 should not loose you anything. Unfortunately, you will have to go back to YUV 4:2:0 for mpeg. I'm not sure what happens in that process ...

PS: My tests were not that scientific. I used the sweep I posted in this thread, and some 75% color bars. A difficulty of the testing is to seperate RGB->YUV conversion errors from YUV->RGB ones. This is because my test material starts life as RGB. I did get better results than overlay, but test for yourself.....

19th February 2004, 05:53	#64 \| Link
trevlac budala Join Date: Oct 2003 Location: U.S. Posts: 545	@Kika This thread got me re-interested in the whole YUV to RGB conversion thing. So I made an avisynth plugin to convert from YUY2 to RGB without changing the range. Basically, I followed Poynton's formulas for studio RGB. The plugin is here. The function is YUY2toRGB219(interpolate=true). Default for interpolation is false. It just does an average across the 2 closest pixels for every other pixel. I did a bunch of testing and here are my basic findings: - YUY2 contains about 25% of the colors available in RGB255 - The remapping that occurs for a normal RGB255->YUV235 changes the colors(not by much) - Converting from RGB->YUV without remapping again changes the colors due to the limits of 8 bit YUV storage - If you go RGB->10 bit YUV and limited remapping, it appears you do not change the colors - Going from YUV->RGB219 and not remapping appears to NOT change the colors. RGB is a big enough space and efficiently uses the 8 bits, so there does not appear to be loss. - Going from YUV->RGB255 can truncate data out of the nominal range. I did not test to see if the remapping looses anything. So... the good news appears to be that if you start with YUV, going to RGB219 should not loose you anything. Unfortunately, you will have to go back to YUV 4:2:0 for mpeg. I'm not sure what happens in that process ... PS: My tests were not that scientific. I used the sweep I posted in this thread, and some 75% color bars. A difficulty of the testing is to seperate RGB->YUV conversion errors from YUV->RGB ones. This is because my test material starts life as RGB. I did get better results than overlay, but test for yourself.....