Specify unspecified gamma instead of lying and saying we use Rec. 709. Again, for...

[nageru] / theme.cpp

diff --git a/theme.cpp b/theme.cpp
index 56d5f84553c5d00bcbb0406c6548ec703fecd059..9914952948477e1a6223f23e298057b9ba34a691 100644 (file)
--- a/theme.cpp
+++ b/theme.cpp
@@ -128,14 +128,26 @@ int EffectChain_finalize(lua_State* L)
        // what's put in the H.264 stream (sps_rbsp()).
        ImageFormat inout_format;
        inout_format.color_space = COLORSPACE_REC_709;
-       inout_format.gamma_curve = GAMMA_REC_709;
+
+       // Output gamma is tricky. We should output Rec. 709 for TV, except that
+       // we expect to run with web players and others that don't really care and
+       // just output with no conversion. So that means we'll need to output sRGB,
+       // even though H.264 has no setting for that (we use “unspecified”).
+       inout_format.gamma_curve = GAMMA_sRGB;
+
        if (is_main_chain) {
                YCbCrFormat output_ycbcr_format;
                // We actually output 4:2:0 in the end, but chroma subsampling
                // happens in a pass not run by Movit (see Mixer::subsample_chroma()).
                output_ycbcr_format.chroma_subsampling_x = 1;
                output_ycbcr_format.chroma_subsampling_y = 1;
-               output_ycbcr_format.luma_coefficients = YCBCR_REC_709;
+
+               // Rec. 709 would be the sane thing to do, but it seems many players
+               // (e.g. MPlayer and VLC) just default to BT.601 coefficients no matter
+               // what (see discussions in e.g. https://trac.ffmpeg.org/ticket/4978).
+               // We _do_ set the right flags, though, so that a player that works
+               // properly doesn't have to guess.
+               output_ycbcr_format.luma_coefficients = YCBCR_REC_601;
                output_ycbcr_format.full_range = false;
                output_ycbcr_format.num_levels = 256;
 
@@ -323,6 +335,13 @@ LiveInputWrapper::LiveInputWrapper(Theme *theme, EffectChain *chain, bool overri
 {
        ImageFormat inout_format;
        inout_format.color_space = COLORSPACE_sRGB;
+
+       // Gamma curve depends on the input signal, and we don't really get any
+       // indications. A camera would be expected to do Rec. 709, but
+       // I haven't checked if any do in practice. However, computers _do_ output
+       // in sRGB gamma (ie., they don't convert from sRGB to Rec. 709), and
+       // I wouldn't really be surprised if most non-professional cameras do, too.
+       // So we pick sRGB as the least evil here.
        inout_format.gamma_curve = GAMMA_sRGB;
 
        // The Blackmagic driver docs claim that the device outputs Y'CbCr