[FFmpeg-devel] 回复: [PATCH v2 3/3] tests/checkasm/vvc_alf: change alf step size to 8

[Wu Jianhua <toqsxw@outlook.com>]

Bross, Benjamin:
> 发件人: Bross, Benjamin <benjamin.bross@hhi.fraunhofer.de>
> 发送时间: 2024年6月3日 3:42
> 收件人: FFmpeg development discussions and patches
> 抄送: Wu Jianhua
> 主题: Re: [FFmpeg-devel] [PATCH v2 3/3] tests/checkasm/vvc_alf: change alf step size to 8
> 
>> From Benjamin Bross:
>>> for ALF where functions are in increments of 4 while 8 should be sufficient according to the spec.
> 
> Actually, it is not only the increment but the size has to be a multiple of 8, hence in addition loops should start at 8 instead of at 4.
> 
> ALF filter and classification is applied on CTU-level.
> According to VVC spec, CTU sizes can be: 32x32, 64x64, 128x128 luma samples.
> However, if width or height are not a multiple of CTU size, the larger CTU is "forced to split" until width or height fits.
> E.g. width=840 luma samples fits 26.25 CTUs, i.e. 26 32x32 and one 8x32.
> Width and height are restricted to be at least a multiple of 8 (see H.266 09/2023, 7.4.3.4 Sequence parameter set RBSP semantics)

> sps_pic_width_max_in_luma_samples shall not be equal to 0 and shall be an integer multiple of
> Max( 8, MinCbSizeY )
> …
> sps_pic_height_max_in_luma_samples shall not be equal to 0 and shall be an integer multiple of
> Max( 8, MinCbSizeY ).
> 
> Please note that this applies only for classification and 7x7 luma filtering. For chroma 5x5 filtering and 420 subsampling, CTU sizes can be as small as multiples of 4 chroma samples.


Hi Benjamin,

I will update some patches according to your comments.

Thanks for your suggestion!
Jianhua
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