[FFmpeg-devel] [PATCH] pgssubdec: fix subpicture output colorspace and range

[Jan Ekström]

Functionality used before didn't widen the values from limited to
full range. Additionally, now the decoder uses BT.709 where it
should be used according to the video resolution.

Default for not yet set colorimetry is BT.709 due to most observed
HDMV content being HD.

BT.709 coefficients were gathered from the first two parts of BT.709
to BT.2020 conversion guide in ARIB STD-B62 (Pt. 1, Chapter 6.2.2).

Based on a patch by Carl Eugen Hoyos.
---
 libavcodec/pgssubdec.c | 20 ++++++++++++++++++--
 libavutil/colorspace.h | 10 ++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/libavcodec/pgssubdec.c b/libavcodec/pgssubdec.c
index 07a2a78..4145f1c 100644
--- a/libavcodec/pgssubdec.c
+++ b/libavcodec/pgssubdec.c
@@ -96,6 +96,7 @@ typedef struct PGSSubContext {
     PGSSubPalettes     palettes;
     PGSSubObjects      objects;
     int forced_subs_only;
+    int hdtv;
 } PGSSubContext;
 
 static void flush_cache(AVCodecContext *avctx)
@@ -136,6 +137,9 @@ static PGSSubPalette * find_palette(int id, PGSSubPalettes *palettes)
 
 static av_cold int init_decoder(AVCodecContext *avctx)
 {
+    PGSSubContext *ctx = avctx->priv_data;
+    ctx->hdtv          = -1;
+
     avctx->pix_fmt     = AV_PIX_FMT_PAL8;
 
     return 0;
@@ -354,8 +358,14 @@ static int parse_palette_segment(AVCodecContext *avctx,
         cb        = bytestream_get_byte(&buf);
         alpha     = bytestream_get_byte(&buf);
 
-        YUV_TO_RGB1(cb, cr);
-        YUV_TO_RGB2(r, g, b, y);
+        /* Default to HDTV (-1 or 1) */
+        if (ctx->hdtv) {
+            YUV_TO_RGB1_CCIR_BT709(cb, cr);
+        } else {
+            YUV_TO_RGB1_CCIR(cb, cr);
+        }
+
+        YUV_TO_RGB2_CCIR(r, g, b, y);
 
         ff_dlog(avctx, "Color %d := (%d,%d,%d,%d)\n", color_id, r, g, b, alpha);
 
@@ -388,6 +398,12 @@ static int parse_presentation_segment(AVCodecContext *avctx,
     int w = bytestream_get_be16(&buf);
     int h = bytestream_get_be16(&buf);
 
+    // Set colorimetry according to resolution
+    if (h > 576)
+        ctx->hdtv = 1;
+    else
+        ctx->hdtv = 0;
+
     ctx->presentation.pts = pts;
 
     ff_dlog(avctx, "Video Dimensions %dx%d\n",
diff --git a/libavutil/colorspace.h b/libavutil/colorspace.h
index 826ffd5..7d3f711 100644
--- a/libavutil/colorspace.h
+++ b/libavutil/colorspace.h
@@ -41,6 +41,16 @@
     b_add = FIX(1.77200*255.0/224.0) * cb + ONE_HALF;\
 }
 
+#define YUV_TO_RGB1_CCIR_BT709(cb1, cr1)\
+{\
+    cb = (cb1) - 128;\
+    cr = (cr1) - 128;\
+    r_add = FIX(1.5747*255.0/224.0) * cr + ONE_HALF;\
+    g_add = - FIX(0.1873*255.0/224.0) * cb - FIX(0.4682*255.0/224.0) * cr + \
+            ONE_HALF;\
+    b_add = FIX(1.8556*255.0/224.0) * cb + ONE_HALF;\
+}
+
 #define YUV_TO_RGB2_CCIR(r, g, b, y1)\
 {\
     y = ((y1) - 16) * FIX(255.0/219.0);\
-- 
2.5.5