(this is rescaled smaller and then larger)
Towards Better Chroma Subsampling - SMPTE Presentation Notes
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Step #2: B'-Y' and R'-Y' components are rescaled smaller and later rescaled to their original size.
The color space conversion can roughly be visualized as this:
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| Original | Luma (Y’) channel only | Color difference components (this is rescaled smaller and then larger) |
Final subsampled image |
For the majority of real world scenes, chroma subsampling works very well and is visually lossless.
*The examples in this presentation are all 4:1:1 (4X horizontal subsampling, no subsampling vertically).
**This particular example uses linear/triangle resampling for the chroma. Other methods will yield different results.