Add sRGB to XYZ matrix

src/matrix.h

@@ -24,6 +24,14 @@ static float XYZD65_to_sRGB[] = {
         // clang-format on
 };
 
+static float sRGB_to_XYZD65[] = {
+        // clang-format off
+        0.4124564f, 0.3575761f, 0.1804375f,
+        0.2126729f, 0.7151522f, 0.0721750f,
+        0.0193339f, 0.1191920f, 0.9503041f,
+        // clang-format on
+};
+
 static float YUV_to_RGB[] = {
         // clang-format off
          0.299f,  0.587f,   0.114f,