Re: [FFmpeg-devel] [PATCH] avutil/pixfmt: fix AV_PIX_FMT_RGB8 description

[Stefano Sabatini <stefasab@gmail.com>]

On date Monday 2024-01-08 09:53:37 -0500, Jeffrey Knockel wrote:
> Previously the description was partially mistaken, explaining the format
> as RGB 3:3:2, (msb)2R 3G 3B(lsb).  While the RGB 3:3:2 part is correct,
> the latter part should be: (msb)3R 3G 2B(lsb). The corresponding bit
> masks are red: 0xE0, green: 0x1C, blue: 0x03.
> 
> Signed-off-by: Jeffrey Knockel <jeff@jeffreyknockel.com>
> ---
>  libavutil/pixfmt.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavutil/pixfmt.h b/libavutil/pixfmt.h
> index 58f9ad28bd..9c87571f49 100644
> --- a/libavutil/pixfmt.h
> +++ b/libavutil/pixfmt.h
> @@ -83,7 +83,7 @@ enum AVPixelFormat {
>      AV_PIX_FMT_BGR8,      ///< packed RGB 3:3:2,  8bpp, (msb)2B 3G 3R(lsb)
>      AV_PIX_FMT_BGR4,      ///< packed RGB 1:2:1 bitstream,  4bpp, (msb)1B 2G 1R(lsb), a byte contains two pixels, the first pixel in the byte is the one composed by the 4 msb bits
>      AV_PIX_FMT_BGR4_BYTE, ///< packed RGB 1:2:1,  8bpp, (msb)1B 2G 1R(lsb)

> -    AV_PIX_FMT_RGB8,      ///< packed RGB 3:3:2,  8bpp, (msb)2R 3G 3B(lsb)
> +    AV_PIX_FMT_RGB8,      ///< packed RGB 3:3:2,  8bpp, (msb)3R 3G 2B(lsb)

This is not consistent with pixdesc definition:
    [AV_PIX_FMT_RGB8] = {
        .name = "rgb8",
        .nb_components = 3,
        .log2_chroma_w = 0,
        .log2_chroma_h = 0,
        .comp = {
            { 0, 1, 0, 6, 2 },        /* R */
            { 0, 1, 0, 3, 3 },        /* G */
            { 0, 1, 0, 0, 3 },        /* B */
        },
        .flags = AV_PIX_FMT_FLAG_RGB,
    },

so either the documentation or the pixdesc description is wrong.

Do you confirm "(msb)3R 3G 2B(lsb)" is the correct definition?

In this case pixdesc should be fixed accordingly.

Thanks.
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