Write TIFF Tag ExtraSamples when encoding pix_fmts that contain transparency information.

libavcodec/tiff.h

@@ -69,6 +69,7 @@ enum TiffTags{
     TIFF_TILE_LENGTH = 0x143,
     TIFF_TILE_OFFSETS = 0x144,
     TIFF_TILE_BYTE_COUNTS = 0x145,
+    TIFF_EXTRASAMPLES = 0x152,
     TIFF_YCBCR_COEFFICIENTS = 0x211,
     TIFF_YCBCR_SUBSAMPLING = 0x212,
     TIFF_YCBCR_POSITIONING = 0x213,

libavcodec/tiffenc.c

@@ -248,7 +248,7 @@ static int encode_frame(AVCodecContext * avctx, AVPacket *pkt,
     uint32_t res[2] = { s->dpi, 1 };        // image resolution (72/1)
     uint16_t bpp_tab[4];
     int ret = -1;
-    int is_yuv = 0;
+    int is_yuv = 0, alpha = 0;
     int shift_h, shift_v;
 
     *p = *pict;
@@ -264,6 +264,7 @@ static int encode_frame(AVCodecContext * avctx, AVPacket *pkt,
     switch (avctx->pix_fmt) {
     case PIX_FMT_RGBA64LE:
     case PIX_FMT_RGBA:
+        alpha = 1;
     case PIX_FMT_RGB48LE:
     case PIX_FMT_RGB24:
         s->photometric_interpretation = 2;
@@ -271,6 +272,7 @@ static int encode_frame(AVCodecContext * avctx, AVPacket *pkt,
     case PIX_FMT_GRAY8:
         avctx->bits_per_coded_sample = 0x28;
     case PIX_FMT_GRAY8A:
+        alpha = avctx->pix_fmt == PIX_FMT_GRAY8A;
     case PIX_FMT_GRAY16LE:
     case PIX_FMT_MONOBLACK:
         s->photometric_interpretation = 1;
@@ -451,6 +453,8 @@ static int encode_frame(AVCodecContext * avctx, AVPacket *pkt,
         }
         add_entry(s, TIFF_PAL, TIFF_SHORT, 256 * 3, pal);
     }
+    if (alpha)
+        add_entry1(s,TIFF_EXTRASAMPLES,      TIFF_SHORT,            2);
     if (is_yuv){
         /** according to CCIR Recommendation 601.1 */
         uint32_t refbw[12] = {15, 1, 235, 1, 128, 1, 240, 1, 128, 1, 240, 1};