vf_colorspace: Add support for ycgco color space

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavfilter/vf_colorspace.c

@@ -175,6 +175,13 @@ typedef struct ColorSpaceContext {
 // FIXME dithering if bitdepth goes down?
 // FIXME bitexact for fate integration?
 
+static const double ycgco_matrix[3][3] =
+{
+    {  0.25, 0.5,  0.25 },
+    { -0.25, 0.5, -0.25 },
+    {  0.5,  0,   -0.5  },
+};
+
 /*
  * All constants explained in e.g. https://linuxtv.org/downloads/v4l-dvb-apis/ch02s06.html
  * The older ones (bt470bg/m) are also explained in their respective ITU docs
@@ -187,6 +194,7 @@ static const struct LumaCoefficients luma_coefficients[AVCOL_SPC_NB] = {
     [AVCOL_SPC_SMPTE170M]  = { 0.299,  0.587,  0.114  },
     [AVCOL_SPC_BT709]      = { 0.2126, 0.7152, 0.0722 },
     [AVCOL_SPC_SMPTE240M]  = { 0.212,  0.701,  0.087  },
+    [AVCOL_SPC_YCOCG]      = { 0.25,   0.5,    0.25   },
     [AVCOL_SPC_BT2020_NCL] = { 0.2627, 0.6780, 0.0593 },
     [AVCOL_SPC_BT2020_CL]  = { 0.2627, 0.6780, 0.0593 },
 };
@@ -209,6 +217,12 @@ static void fill_rgb2yuv_table(const struct LumaCoefficients *coeffs,
 {
     double bscale, rscale;
 
+    // special ycgco matrix
+    if (coeffs->cr == 0.25 && coeffs->cg == 0.5 && coeffs->cb == 0.25) {
+        memcpy(rgb2yuv, ycgco_matrix, sizeof(double) * 9);
+        return;
+    }
+
     rgb2yuv[0][0] = coeffs->cr;
     rgb2yuv[0][1] = coeffs->cg;
     rgb2yuv[0][2] = coeffs->cb;
@@ -1047,6 +1061,7 @@ static const AVOption colorspace_options[] = {
     ENUM("bt470bg",     AVCOL_SPC_BT470BG,     "csp"),
     ENUM("smpte170m",   AVCOL_SPC_SMPTE170M,   "csp"),
     ENUM("smpte240m",   AVCOL_SPC_SMPTE240M,   "csp"),
+    ENUM("ycgco",       AVCOL_SPC_YCGCO,       "csp"),
     ENUM("bt2020ncl",   AVCOL_SPC_BT2020_NCL,  "csp"),
 
     { "range",      "Output color range",