AV1: Bit depth of a reference image query

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Jason matis

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Oct 11, 2021, 2:40:22 AMOct 11
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Good morning.

Is there a possibility to use bit depth of a reference image smaller than that of the image in the enhancement layer? I was reviewing the AV1 specification and it appears that the bit depth of the entire coded video sequence (which includes both the base and enhancement layer) is the same.

Is my understanding correct or is it possible to use bit depth of a reference image smaller than that of the image in the enhancement layer?


Thanks

Jason

Wan-Teh Chang

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Oct 11, 2021, 12:29:30 PMOct 11
to av1-d...@aomedia.org
Hi Jadon,

Your understanding is correct. The bit depth of a coded video sequence
is specified in the sequence header OBU and applies to all the layers
in the coded video sequence. You can verify this by searching for
"BitDepth = " in the AV1 specification. You will see that the BitDepth
variable is only set in the color_config() function, which is called
only by the sequence_header_obu() function.

See also this requirement of bitstream conformance on page 153:

ref_frame_idx[ i ] specifies which reference frames are used by inter
frames. It is a requirement of bitstream conformance that RefValid[
ref_frame_idx[ i ] ] is equal to 1, and that the selected reference
frames match the current frame in bit depth, profile, chroma
subsampling, and color space.

Wan-Teh Chang

Jason matis

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Oct 13, 2021, 1:02:01 AMOct 13
to AV1 Discussion
Thank you Wan-Teh Chang. Appreciate it.

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