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

[Leo Izen <leo.izen@gmail.com>]

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 ++++++++++++++++++++++++++------------------
 1 file changed, 75 insertions(+), 51 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;
+    }
+
+    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) {
-- 
2.39.1

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