Re: [FFmpeg-devel] [PATCH v2 2/2] avcodec/pngdec: read colorspace info when decoding with AVDISCARD_ALL

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

Leo Izen:
> These chunks are lightweight and it's useful information to have when
> running ffmpeg -i or ffprobe, for example.
> 
> Signed-off-by: Leo Izen <leo.izen@gmail.com>
> ---
>  libavcodec/pngdec.c          | 126 +++++++++++++++++++++--------------
>  tests/ref/fate/png-icc       |   8 +--
>  tests/ref/fate/png-side-data |   2 +-
>  3 files changed, 80 insertions(+), 56 deletions(-)
> 
> diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
> index 0d969decf2..c83da08eb9 100644
> --- a/libavcodec/pngdec.c
> +++ b/libavcodec/pngdec.c
> @@ -75,6 +75,7 @@ typedef struct PNGDecContext {
>      int have_chrm;
>      uint32_t white_point[2];
>      uint32_t display_primaries[3][2];
> +    int gamma;
>      int have_srgb;
>      int have_cicp;
>      enum AVColorPrimaries cicp_primaries;
> @@ -1203,7 +1204,7 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
>  
>              if (avctx->codec_id == AV_CODEC_ID_PNG &&
>                  avctx->skip_frame == AVDISCARD_ALL) {
> -                return 0;
> +                goto exit_loop;
>              }
>  
>              if (CONFIG_APNG_DECODER && avctx->codec_id == AV_CODEC_ID_APNG && length == 0) {
> @@ -1256,6 +1257,10 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
>              case MKTAG('t', 'E', 'X', 't'):
>              case MKTAG('I', 'D', 'A', 'T'):
>              case MKTAG('t', 'R', 'N', 'S'):
> +            case MKTAG('s', 'R', 'G', 'B'):
> +            case MKTAG('c', 'I', 'C', 'P'):
> +            case MKTAG('c', 'H', 'R', 'M'):
> +            case MKTAG('g', 'A', 'M', 'A'):
>                  break;
>              default:
>                  continue;
> @@ -1358,10 +1363,10 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
>          case MKTAG('g', 'A', 'M', 'A'): {
>              AVBPrint bp;
>              char *gamma_str;
> -            int num = bytestream2_get_be32(&gb_chunk);
> +            s->gamma = bytestream2_get_be32(&gb_chunk);
>  
>              av_bprint_init(&bp, 0, AV_BPRINT_SIZE_UNLIMITED);
> -            av_bprintf(&bp, "%i/%i", num, 100000);
> +            av_bprintf(&bp, "%i/%i", s->gamma, 100000);
>              ret = av_bprint_finalize(&bp, &gamma_str);
>              if (ret < 0)
>                  return ret;
> @@ -1382,6 +1387,73 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
>      }
>  exit_loop:
>  
> +    if (s->have_cicp) {
> +        if (s->cicp_primaries >= AVCOL_PRI_NB)
> +            av_log(avctx, AV_LOG_WARNING, "unrecognized cICP primaries\n");
> +        else
> +            avctx->color_primaries = p->color_primaries = s->cicp_primaries;
> +        if (s->cicp_trc >= AVCOL_TRC_NB)
> +            av_log(avctx, AV_LOG_WARNING, "unrecognized cICP transfer\n");
> +        else
> +            avctx->color_trc = p->color_trc = s->cicp_trc;
> +        /* we don't support tv-range RGB */
> +        avctx->color_range = p->color_range = AVCOL_RANGE_JPEG;
> +        if (s->cicp_range == 0)
> +            av_log(avctx, AV_LOG_WARNING, "unsupported tv-range cICP chunk\n");
> +    } else if (s->iccp_data) {
> +        AVFrameSideData *sd = av_frame_new_side_data(p, AV_FRAME_DATA_ICC_PROFILE, s->iccp_data_len);
> +        if (!sd) {
> +            ret = AVERROR(ENOMEM);
> +            goto fail;
> +        }
> +        memcpy(sd->data, s->iccp_data, s->iccp_data_len);
> +
> +        av_dict_set(&sd->metadata, "name", s->iccp_name, 0);
> +    } else if (s->have_srgb) {
> +        avctx->color_primaries = p->color_primaries = AVCOL_PRI_BT709;
> +        avctx->color_trc = p->color_trc = AVCOL_TRC_IEC61966_2_1;
> +    } else if (s->have_chrm) {
> +        AVColorPrimariesDesc desc;
> +        enum AVColorPrimaries prim;
> +        desc.wp.x = av_make_q(s->white_point[0], 100000);
> +        desc.wp.y = av_make_q(s->white_point[1], 100000);
> +        desc.prim.r.x = av_make_q(s->display_primaries[0][0], 100000);
> +        desc.prim.r.y = av_make_q(s->display_primaries[0][1], 100000);
> +        desc.prim.g.x = av_make_q(s->display_primaries[1][0], 100000);
> +        desc.prim.g.y = av_make_q(s->display_primaries[1][1], 100000);
> +        desc.prim.b.x = av_make_q(s->display_primaries[2][0], 100000);
> +        desc.prim.b.y = av_make_q(s->display_primaries[2][1], 100000);
> +        prim = av_csp_primaries_id_from_desc(&desc);
> +        if (prim != AVCOL_PRI_UNSPECIFIED)
> +            avctx->color_primaries = p->color_primaries = prim;
> +        else
> +            av_log(avctx, AV_LOG_WARNING, "unknown cHRM primaries\n");
> +    }
> +
> +    /* these chunks override gAMA */
> +    if (s->iccp_data || s->have_srgb || s->have_cicp) {
> +        av_dict_set(&s->frame_metadata, "gamma", NULL, 0);
> +    } else if (s->gamma) {
> +        /*
> +         * these values are 100000/2.2, 100000/2.8, and 100000/2.6
> +         * respectively. 45455, 35714, and 38462. There's a 0.001
> +         * gamma tolerance here in case of floating point issues
> +         * when the PNG was written.
> +         *
> +         * None of the other enums have a pure gamma curve so it makes
> +         * sense to leave those to sRGB and cICP.
> +         */
> +        if (s->gamma > 45355 && s->gamma < 45555)
> +            avctx->color_trc = p->color_trc = AVCOL_TRC_GAMMA22;
> +        else if (s->gamma > 35614 && s->gamma < 35814)
> +            avctx->color_trc = p->color_trc = AVCOL_TRC_GAMMA28;
> +        else if (s->gamma > 38362 && s->gamma < 38562)
> +            avctx->color_trc = p->color_trc = AVCOL_TRC_SMPTE428;

It seems that this patch does more than the commit message claims.

> +    }
> +
> +    avctx->colorspace = p->colorspace = AVCOL_SPC_RGB;
> +    avctx->color_range = p->color_range = AVCOL_RANGE_JPEG;
> +
>      if (avctx->codec_id == AV_CODEC_ID_PNG &&
>          avctx->skip_frame == AVDISCARD_ALL) {
>          return 0;
> @@ -1499,56 +1571,8 @@ static void clear_frame_metadata(PNGDecContext *s)
>  
>  static int output_frame(PNGDecContext *s, AVFrame *f)
>  {
> -    AVCodecContext *avctx = s->avctx;
>      int ret;
>  
> -    if (s->have_cicp) {
> -        if (s->cicp_primaries >= AVCOL_PRI_NB)
> -            av_log(avctx, AV_LOG_WARNING, "unrecognized cICP primaries\n");
> -        else
> -            avctx->color_primaries = f->color_primaries = s->cicp_primaries;
> -        if (s->cicp_trc >= AVCOL_TRC_NB)
> -            av_log(avctx, AV_LOG_WARNING, "unrecognized cICP transfer\n");
> -        else
> -            avctx->color_trc = f->color_trc = s->cicp_trc;
> -        avctx->color_range = f->color_range =
> -            s->cicp_range == 0 ? AVCOL_RANGE_MPEG : AVCOL_RANGE_JPEG;
> -    } else if (s->iccp_data) {
> -        AVFrameSideData *sd = av_frame_new_side_data(f, AV_FRAME_DATA_ICC_PROFILE, s->iccp_data_len);
> -        if (!sd) {
> -            ret = AVERROR(ENOMEM);
> -            goto fail;
> -        }
> -        memcpy(sd->data, s->iccp_data, s->iccp_data_len);
> -
> -        av_dict_set(&sd->metadata, "name", s->iccp_name, 0);
> -    } else if (s->have_srgb) {
> -        avctx->color_primaries = f->color_primaries = AVCOL_PRI_BT709;
> -        avctx->color_trc = f->color_trc = AVCOL_TRC_IEC61966_2_1;
> -    } else if (s->have_chrm) {
> -        AVColorPrimariesDesc desc;
> -        enum AVColorPrimaries prim;
> -        desc.wp.x = av_make_q(s->white_point[0], 100000);
> -        desc.wp.y = av_make_q(s->white_point[1], 100000);
> -        desc.prim.r.x = av_make_q(s->display_primaries[0][0], 100000);
> -        desc.prim.r.y = av_make_q(s->display_primaries[0][1], 100000);
> -        desc.prim.g.x = av_make_q(s->display_primaries[1][0], 100000);
> -        desc.prim.g.y = av_make_q(s->display_primaries[1][1], 100000);
> -        desc.prim.b.x = av_make_q(s->display_primaries[2][0], 100000);
> -        desc.prim.b.y = av_make_q(s->display_primaries[2][1], 100000);
> -        prim = av_csp_primaries_id_from_desc(&desc);
> -        if (prim != AVCOL_PRI_UNSPECIFIED)
> -            avctx->color_primaries = f->color_primaries = prim;
> -        else
> -            av_log(avctx, AV_LOG_WARNING, "unknown cHRM primaries\n");
> -    }
> -
> -    /* these chunks override gAMA */
> -    if (s->iccp_data || s->have_srgb || s->have_cicp)
> -        av_dict_set(&s->frame_metadata, "gamma", NULL, 0);
> -
> -    avctx->colorspace = f->colorspace = AVCOL_SPC_RGB;
> -
>      if (s->stereo_mode >= 0) {
>          AVStereo3D *stereo3d = av_stereo3d_create_side_data(f);
>          if (!stereo3d) {
> diff --git a/tests/ref/fate/png-icc b/tests/ref/fate/png-icc
> index 14de544639..1f4eab1fb0 100644
> --- a/tests/ref/fate/png-icc
> +++ b/tests/ref/fate/png-icc
> @@ -1,5 +1,5 @@
> -a50d37a0e72bddea2fcbba6fb773e2a0 *tests/data/fate/png-icc.image2
> -49397 tests/data/fate/png-icc.image2
> +c460cd06a88ace94d7c76a6309aa8fb8 *tests/data/fate/png-icc.image2
> +49441 tests/data/fate/png-icc.image2
>  #tb 0: 1/25
>  #media_type 0: video
>  #codec_id 0: rawvideo
> @@ -21,7 +21,7 @@ pkt_duration_time=0.040000
>  duration=1
>  duration_time=0.040000
>  pkt_pos=0
> -pkt_size=49397
> +pkt_size=49441
>  width=128
>  height=128
>  pix_fmt=rgb24
> @@ -34,7 +34,7 @@ top_field_first=0
>  repeat_pict=0
>  color_range=pc
>  color_space=gbr
> -color_primaries=unknown
> +color_primaries=bt709
>  color_transfer=unknown
>  chroma_location=unspecified
>  [SIDE_DATA]
> diff --git a/tests/ref/fate/png-side-data b/tests/ref/fate/png-side-data
> index a4c16eb395..8f955f76bc 100644
> --- a/tests/ref/fate/png-side-data
> +++ b/tests/ref/fate/png-side-data
> @@ -26,7 +26,7 @@ top_field_first=0
>  repeat_pict=0
>  color_range=pc
>  color_space=gbr
> -color_primaries=unknown
> +color_primaries=bt709
>  color_transfer=unknown
>  chroma_location=unspecified
>  [SIDE_DATA]

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