Towards Better Chroma Subsampling - SMPTE Presentation Notes
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Out of range/gamut colors
- Suppose there is an image consisting of red lines on a black background.
 -->  |
| Original values |
|
|
| Y’ |
0.2126 |
0 |
| B’-Y’ |
-0.2126 |
0 |
| R’-Y’ |
0.7874 |
0 |
| Subsampled values |
|
|
| Y' |
0.2126 |
0 |
| B'-Y' |
-0.1063 |
- |
| R'-Y' |
0.3937 |
- |
| R'G'B' values |
|
|
| R' |
0.6063 |
0.3937 |
| G' |
0.1063 |
-0.1063 |
| B' |
0.1063 |
-0.1063 |
|
- The black pixels end up with positive red and also negative green
and blue values.
- Negative light does not exist! Negative green and blue cannot be reproduced.
- The originally-black pixels end up too bright while the originally-red pixels
end up too dark and undersaturated.
- A similar effect occurs with chroma reconstructed onto white pixels.