Towards Better Chroma Subsampling - SMPTE Presentation Notes
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Non-Constant Luminance
- Chroma subsampling does not maintain constant luminance.
The calculation of luma only approximates luminance.
- To maintain constant luminance, it must be calculated in the linear light
domain. Convert the R'G'B' values to linear light RGB values, calculate luminance,
then convert back to gamma-corrected R'G'B' values.
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| Original |
Typical processing |
Linear light processing |
- Errors in chroma affect luminance, resulting in dark bands where color transitions
occur.
- These errors are proportional to chroma strength. In real world scenery
(except titles), colors tend not to be highly saturated so these errors rarely
appear.
- Linear light processing solves the problem of non-constant luminance if
it is used in both (1) forming luminance and (2) in resampling/rescaling the
chroma.