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

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

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;
+            }
+        }
+    }
+
     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;
-- 
2.39.2

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