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Introducing Daala part 4: Chroma from Luma (xiph video codec)

53 points by jobstijl 13y ago

deleted 13y ago
[deleted]
quink 13y ago
Thank you Monty! Awesome as always and already waiting for the next part - no pressure :) And just because I know someone is going to ask: Motion prediction in H.264 is based on luma, but there's also a chroma option. I've done some quick searches and found a patent for HEVC that covers using the correlation for motion prediction.
jobstijl 13y ago
xiphmont_: huh demo4:CfL is on HN already jobstijl0: I posted it, didn't saw you where still working on it xiphmont: ah, it wasn't actually due to be up for real until I got back from vacation in two weeks xiphmont: no harm, just 'agh, nothing is tested yet!'
- quink 13y ago
  I noticed > [some RDO graphs will be nice-- add these]
Gravityloss 13y ago
"Luma predicts from luma, and chroma predicts from chroma. There's little or no attempt to account for remaining cross-channel correlation." Interesting, would have thought these are one of the first things to try...
- walrus 13y ago
  They did try in HEVC! It was scrapped because it decreased the encoder performance and its benefits didn't show up in their primary test metric (PSNR).
forgottenpaswrd 13y ago
Great tutorial. They use some terms like DC(or TF) without explaining what they mean. I could not understand them without significant effort. For example, for "DC" I know(after careful analysis) that they mean constant average value, it could mean Discrete Cosine, or Discrete Component. What does it mean? "Direct current"? How Direct current will make any sense in a digital signal article?
- nimrody 13y ago
  DC is the low frequency (zero frequency) component of the signal and is indeed obtained by simple averaging.
- walrus 13y ago
  The term DC is borrowed from electrical engineering. https://en.wikipedia.org/wiki/DC_bias https://en.wikipedia.org/wiki/DC_bias explains: The term originated in electronics, where it refers to a direct current voltage, but the concept has been extended to any representation of a waveform. The term's use is extended to two-dimensional transformations like the discrete cosine transform used in JPEG. TF is defined in the previous demo page, http://people.xiph.org/~xiphmont/demo/daala/demo3.shtml http://people.xiph.org/~xiphmont/demo/daala/demo3.shtml. It means Time/Frequency Resolution Switching, a idea from Xiph's Opus codec.

53 points by jobstijl 13y ago

deleted 13y ago

[deleted]

quink 13y ago

Thank you Monty! Awesome as always and already waiting for the next part - no pressure :) And just because I know someone is going to ask: Motion prediction in H.264 is based on luma, but there's also a chroma option. I've done some quick searches and found a patent for HEVC that covers using the correlation for motion prediction.

jobstijl 13y ago

xiphmont_: huh demo4:CfL is on HN already jobstijl0: I posted it, didn't saw you where still working on it xiphmont: ah, it wasn't actually due to be up for real until I got back from vacation in two weeks xiphmont: no harm, just 'agh, nothing is tested yet!'

quink 13y ago
I noticed > [some RDO graphs will be nice-- add these]

Gravityloss 13y ago

"Luma predicts from luma, and chroma predicts from chroma. There's little or no attempt to account for remaining cross-channel correlation." Interesting, would have thought these are one of the first things to try...

walrus 13y ago
They did try in HEVC! It was scrapped because it decreased the encoder performance and its benefits didn't show up in their primary test metric (PSNR).

forgottenpaswrd 13y ago

Great tutorial. They use some terms like DC(or TF) without explaining what they mean. I could not understand them without significant effort. For example, for "DC" I know(after careful analysis) that they mean constant average value, it could mean Discrete Cosine, or Discrete Component. What does it mean? "Direct current"? How Direct current will make any sense in a digital signal article?

nimrody 13y ago
DC is the low frequency (zero frequency) component of the signal and is indeed obtained by simple averaging.
walrus 13y ago
The term DC is borrowed from electrical engineering. https://en.wikipedia.org/wiki/DC_bias https://en.wikipedia.org/wiki/DC_bias explains: The term originated in electronics, where it refers to a direct current voltage, but the concept has been extended to any representation of a waveform. The term's use is extended to two-dimensional transformations like the discrete cosine transform used in JPEG. TF is defined in the previous demo page, http://people.xiph.org/~xiphmont/demo/daala/demo3.shtml http://people.xiph.org/~xiphmont/demo/daala/demo3.shtml. It means Time/Frequency Resolution Switching, a idea from Xiph's Opus codec.