Add somewhat speculative Rec 1886 and Rec 2020 colour conversions.

3 files changed, 46 insertions, 1 deletions

diff --git a/src/colour_conversion.cc b/src/colour_conversion.cc
index 8c48c2e1..46bc717e 100644
--- a/src/colour_conversion.cc
+++ b/src/colour_conversion.cc
@@ -97,6 +97,44 @@ ColourConversion::p3_to_xyz ()
 	return *c;
 }
 
+ColourConversion const &
+ColourConversion::rec1886_to_xyz ()
+{
+	/* According to Olivier on DCP-o-matic bug #832, Rec. 1886 is Rec. 709 with
+	   2.4 gamma, so here goes ...
+	*/
+	static ColourConversion* c = new ColourConversion (
+		shared_ptr<const TransferFunction> (new GammaTransferFunction (2.4)),
+		YUV_TO_RGB_REC709,
+		Chromaticity (0.64, 0.33),
+		Chromaticity (0.3, 0.6),
+		Chromaticity (0.15, 0.06),
+		/* D65 */
+		Chromaticity (0.3127, 0.329),
+		optional<Chromaticity> (),
+		shared_ptr<const TransferFunction> (new GammaTransferFunction (2.6))
+		);
+	return *c;
+}
+
+ColourConversion const &
+ColourConversion::rec2020_to_xyz ()
+{
+	/* From Wikipedia */
+	static ColourConversion* c = new ColourConversion (
+		shared_ptr<const TransferFunction> (new ModifiedGammaTransferFunction (1 / 0.45, 0.08145, 0.0993, 4.5)),
+		YUV_TO_RGB_REC709,
+		Chromaticity (0.708, 0.292),
+		Chromaticity (0.170, 0.797),
+		Chromaticity (0.131, 0.046),
+		/* D65 */
+		Chromaticity (0.3127, 0.329),
+		optional<Chromaticity> (),
+		shared_ptr<const TransferFunction> (new GammaTransferFunction (2.6))
+		);
+	return *c;
+}
+
 ColourConversion::ColourConversion (
 	shared_ptr<const TransferFunction> in,
 	YUVToRGB yuv_to_rgb,
diff --git a/src/colour_conversion.h b/src/colour_conversion.h
index 47071dd1..f974a182 100644
--- a/src/colour_conversion.h
+++ b/src/colour_conversion.h
@@ -139,6 +139,8 @@ public:
 	static ColourConversion const & rec601_to_xyz ();
 	static ColourConversion const & rec709_to_xyz ();
 	static ColourConversion const & p3_to_xyz ();
+	static ColourConversion const & rec1886_to_xyz ();
+	static ColourConversion const & rec2020_to_xyz ();
 
 protected:
 	/** Input transfer function (probably a gamma function, or something similar) */
diff --git a/src/modified_gamma_transfer_function.h b/src/modified_gamma_transfer_function.h
index e8875d4b..c200743a 100644
--- a/src/modified_gamma_transfer_function.h
+++ b/src/modified_gamma_transfer_function.h
@@ -25,10 +25,15 @@
 
 namespace dcp {
 
-/** A transfer function which for an input x gives an output y where
+/** A transfer function which for an input x gives a linear output y where
  *
  *  y = x / B                      for x <= threshold
  *  y = ((x + A) / (1 + A))^power  for x >  threshold
+ *
+ *  The reverse transform is
+ *
+ *  x = y * B                          for y <= threshold / B
+ *  x = (1 + A) * y ^ (1 / power) - A  for y >  threshold / B
  */
 class ModifiedGammaTransferFunction : public TransferFunction
 {