Try non-linearised gamma of 2.4 for Rec 2020.

Some discussion of this on #892.  Also influenced by discussions
with Dennis (email Tue, 30 Jun 2015) on how the oft-quoted
(e.g. by Wikipedia) gamma functions are camera transforms and not
intended for uses like ours.

Also see ITU-r BT1886 which talks about a gamma of 2.4.

diff --git a/src/colour_conversion.cc b/src/colour_conversion.cc
index be5e999c4955b54f175a826553393fa4f4d666dd..aa22a615bddb727e93dc52baa87ab9bbd330885f 100644 (file)
--- a/src/colour_conversion.cc
+++ b/src/colour_conversion.cc
@@ -134,9 +134,8 @@ ColourConversion::rec1886_to_xyz ()
 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)),
+               shared_ptr<const TransferFunction> (new GammaTransferFunction (2.4)),
                YUV_TO_RGB_REC709,
                Chromaticity (0.708, 0.292),
                Chromaticity (0.170, 0.797),