[FFmpeg-devel] [PATCH] avcodec/pngdec: improve handling of bad cICP range tags

[Leo Izen]

FFmpeg doesn't support tv-range RGB throughout most of its pipeline, so
we should keep the warning. However, in case something does support it
we should at least keep it tagged properly. Additionally, the encoder
writes this tag if the space is tagged as such so this makes a round
trip work as it should.

Also, PNG doesn't support nonzero matrices but we only warn and ignore
in that case, so we have no reason to error out for illegal cICP ranges
either (i.e. greater than 1).

Signed-off-by: Leo Izen <leo.izen at gmail.com>
Reported-by: Kacper Michajłow <kasper93 at gmail.com>
---
 libavcodec/pngdec.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
index d812ffd348..d1aae4c70e 100644
--- a/libavcodec/pngdec.c
+++ b/libavcodec/pngdec.c
@@ -661,8 +661,13 @@ static int populate_avctx_color_fields(AVCodecContext *avctx, AVFrame *frame)
             av_log(avctx, AV_LOG_WARNING, "unrecognized cICP transfer\n");
         else
             avctx->color_trc = frame->color_trc = s->cicp_trc;
-        if (s->cicp_range == 0)
-            av_log(avctx, AV_LOG_WARNING, "unsupported tv-range cICP chunk\n");
+        if (s->cicp_range == 0) {
+            av_log(avctx, AV_LOG_WARNING, "tv-range cICP tag found. Colors may be wrong\n");
+            avctx->color_range = frame->color_range = AVCOL_RANGE_MPEG;
+        } else if (s->cicp_range != 1) {
+            /* we already printed a warning when parsing the cICP chunk */
+            avctx->color_range = frame->color_range = AVCOL_RANGE_UNSPECIFIED;
+        }
     } else if (s->iccp_data) {
         AVFrameSideData *sd = av_frame_new_side_data(frame, AV_FRAME_DATA_ICC_PROFILE, s->iccp_data_len);
         if (!sd)
@@ -713,9 +718,10 @@ static int populate_avctx_color_fields(AVCodecContext *avctx, AVFrame *frame)
             avctx->color_trc = frame->color_trc = AVCOL_TRC_LINEAR;
     }
 
-    /* we only support pc-range RGB */
+    /* PNG only supports RGB */
     avctx->colorspace = frame->colorspace = AVCOL_SPC_RGB;
-    avctx->color_range = frame->color_range = AVCOL_RANGE_JPEG;
+    if (!s->have_cicp || s->cicp_range == 1)
+        avctx->color_range = frame->color_range = AVCOL_RANGE_JPEG;
 
     /*
      * tRNS sets alpha depth to full, so we ignore sBIT if set.
@@ -1455,11 +1461,8 @@ static int decode_frame_common(AVCodecContext *avctx, PNGDecContext *s,
             if (bytestream2_get_byte(&gb_chunk) != 0)
                 av_log(avctx, AV_LOG_WARNING, "nonzero cICP matrix\n");
             s->cicp_range = bytestream2_get_byte(&gb_chunk);
-            if (s->cicp_range != 0 && s->cicp_range != 1) {
-                av_log(avctx, AV_LOG_ERROR, "invalid cICP range: %d\n", s->cicp_range);
-                ret = AVERROR_INVALIDDATA;
-                goto fail;
-            }
+            if (s->cicp_range != 0 && s->cicp_range != 1)
+                av_log(avctx, AV_LOG_WARNING, "invalid cICP range: %d\n", s->cicp_range);
             s->have_cicp = 1;
             break;
         case MKTAG('s', 'R', 'G', 'B'):
@@ -1814,8 +1817,6 @@ static av_cold int png_dec_init(AVCodecContext *avctx)
 {
     PNGDecContext *s = avctx->priv_data;
 
-    avctx->color_range = AVCOL_RANGE_JPEG;
-
     s->avctx = avctx;
     s->last_picture.f = av_frame_alloc();
     s->picture.f = av_frame_alloc();
-- 
2.43.0