Re: [FFmpeg-devel] [PATCH] avcodec/mjpegdec: support weird RGB subsampling with progressive

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Leo Izen:
> This allows weird subsampling with progressive JPEGs to be decoded,
> such as full-RG and only B subsampled.
> ---
>  libavcodec/mjpegdec.c | 38 ++++++++++++++++++++++++++++----------
>  1 file changed, 28 insertions(+), 10 deletions(-)
> 
> diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c
> index c833d66c4d..062730f3e1 100644
> --- a/libavcodec/mjpegdec.c
> +++ b/libavcodec/mjpegdec.c
> @@ -571,10 +571,15 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
>          case 0x22221100:
>          case 0x22112200:
>          case 0x11222200:
> -            if (s->bits <= 8) s->avctx->pix_fmt = s->cs_itu601 ? AV_PIX_FMT_YUV444P : AV_PIX_FMT_YUVJ444P;
> -            else
> +            if (s->bits > 8)
>                  goto unk_pixfmt;
> -            s->avctx->color_range = s->cs_itu601 ? AVCOL_RANGE_MPEG : AVCOL_RANGE_JPEG;
> +            if (s->adobe_transform == 0 || s->component_id[0] == 'R' &&
> +                    s->component_id[1] == 'G' && s->component_id[2] == 'B') {
> +                s->avctx->pix_fmt = AV_PIX_FMT_GBRP;
> +            } else {
> +                s->avctx->pix_fmt = s->cs_itu601 ? AV_PIX_FMT_YUV444P : AV_PIX_FMT_YUVJ444P;
> +                s->avctx->color_range = s->cs_itu601 ? AVCOL_RANGE_MPEG : AVCOL_RANGE_JPEG;
> +            }
>              break;
>          case 0x11000000:
>          case 0x13000000:
> @@ -673,10 +678,6 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
>              avpriv_report_missing_feature(s->avctx, "Lowres for weird subsampling");
>              return AVERROR_PATCHWELCOME;
>          }
> -        if ((AV_RB32(s->upscale_h) || AV_RB32(s->upscale_v)) && s->progressive && s->avctx->pix_fmt == AV_PIX_FMT_GBRP) {
> -            avpriv_report_missing_feature(s->avctx, "progressive for weird subsampling");
> -            return AVERROR_PATCHWELCOME;
> -        }
>          if (s->ls) {
>              memset(s->upscale_h, 0, sizeof(s->upscale_h));
>              memset(s->upscale_v, 0, sizeof(s->upscale_v));
> @@ -1697,9 +1698,6 @@ int ff_mjpeg_decode_sos(MJpegDecodeContext *s, const uint8_t *mb_bitmask,
>          s->h_scount[i]  = s->h_count[index];
>          s->v_scount[i]  = s->v_count[index];
>  
> -        if((nb_components == 1 || nb_components == 3) && s->nb_components == 3 && s->avctx->pix_fmt == AV_PIX_FMT_GBR24P)
> -            index = (index+2)%3;
> -
>          s->comp_index[i] = index;
>  
>          s->dc_index[i] = get_bits(&s->gb, 4);
> @@ -2745,6 +2743,26 @@ the_end:
>              }
>          }
>      }
> +
> +    if (s->avctx->pix_fmt == AV_PIX_FMT_GBRP) {
> +        int w = s->picture_ptr->width;
> +        int h = s->picture_ptr->height;
> +        av_assert0(s->nb_components == 3);
> +        for (int i = 0; i < h; i++) {
> +            uint8_t *dst[3];
> +            for (int index = 0; index < 3; index++)
> +                dst[index] = s->picture_ptr->data[index] + i * s->picture_ptr->linesize[index];
> +            for (int j = 0; j < w; j++) {
> +                uint8_t r = dst[0][j];
> +                uint8_t g = dst[1][j];
> +                uint8_t b = dst[2][j];
> +                dst[0][j] = g;
> +                dst[1][j] = b;
> +                dst[2][j] = r;
> +            }
> +        }
> +    }

Is there a reason you are not just swapping the pointers?

> +
>      if (s->adobe_transform == 2 && s->avctx->pix_fmt == AV_PIX_FMT_YUVA444P) {
>          int w = s->picture_ptr->width;
>          int h = s->picture_ptr->height;

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