[FFmpeg-devel] [PATCH v2 1/8] swscale: document SWS_FULL_CHR_H_* flags

[Niklas Haas]

On Thu, 04 Jul 2024 16:30:57 +0200 Niklas Haas <ffmpeg at haasn.xyz> wrote:
> From: Niklas Haas <git at haasn.dev>
> 
> Based on my best understanding of what they do, given the source code.
> ---
>  libswscale/swscale.h | 28 ++++++++++++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/libswscale/swscale.h b/libswscale/swscale.h
> index 9d4612aaf3..e22931cab4 100644
> --- a/libswscale/swscale.h
> +++ b/libswscale/swscale.h
> @@ -82,11 +82,35 @@ const char *swscale_license(void);
>  #define SWS_PRINT_INFO              0x1000
>  
>  //the following 3 flags are not completely implemented
> -//internal chrominance subsampling info
> +
> +/**
> + * Perform full chroma upsampling when converting to RGB as part of scaling.
> + *
> + * For example, when converting 50x50 yuv420p to 100x100 rgba, setting this flag
> + * will scale the chroma plane from 25x25 to 100x100 (4:4:4), and then convert
> + * the 100x100 yuv444p image to rgba in the final output step.
> + *
> + * Without this flag, the chroma plane is instead scaled to 50x100 (4:2:2),
> + * with a single chroma sample being re-used for both horizontally adjacent RGBA
> + * output pixels.
> + */
>  #define SWS_FULL_CHR_H_INT    0x2000
> -//input subsampling info
> +
> +/**
> + * Perform full chroma interpolation when downscaling RGB sources.
> + *
> + * For example, when converting a 100x100 rgba source to 50x50 yuv444p, setting
> + * this flag will generate a 100x100 (4:4:4) chroma plane, which is then
> + * downscaled to the required 50x50.
> + *
> + * Without this flag, the chroma plane is instead generated at 50x100 (dropping
> + * every other pixel), before then being downscaled to the required 50x50
> + * resolution.
> + */
>  #define SWS_FULL_CHR_H_INP    0x4000
> +
>  #define SWS_DIRECT_BGR        0x8000
> +
>  #define SWS_ACCURATE_RND      0x40000
>  #define SWS_BITEXACT          0x80000
>  #define SWS_ERROR_DIFFUSION  0x800000
> -- 
> 2.45.2
> 

Forgot about this one. Merged as 68957f58..1b9c89c64.