vo_opengl: use more precise gamma for BT.709 with color management

Change from gamma 2.2 to the slightly more precise 1/0.45 as per BT.709.

https://www.itu.int/rec/R-REC-BT.709-5-200204-I/en mentions a value of
γ=0.45 for the conceptual non-linear precorrection of video signals.

This is approximately the inverse of 2.22, and not 2.20 as the code had
been using until now.

2 files changed, 5 insertions, 5 deletions

diff --git a/video/out/vo_opengl.c b/video/out/vo_opengl.c
index 9e333b90b5..d1808af265 100644
--- a/video/out/vo_opengl.c
+++ b/video/out/vo_opengl.c
@@ -1908,7 +1908,7 @@ static bool load_icc(struct gl_priv *p, const char *icc_file,
         .Green = {0.30, 0.60, 1.0},
         .Blue  = {0.15, 0.06, 1.0},
     };
-    cmsToneCurve *tonecurve = cmsBuildGamma(NULL, 2.2);
+    cmsToneCurve *tonecurve = cmsBuildGamma(NULL, 1.0/0.45);
     cmsHPROFILE vid_profile = cmsCreateRGBProfile(&d65, &bt709prim,
                         (cmsToneCurve*[3]){tonecurve, tonecurve, tonecurve});
     cmsFreeToneCurve(tonecurve);
@@ -2318,7 +2318,7 @@ static const char help_text[] =
 "    Enable gamma-correct scaling by working in linear light. This\n"
 "    makes use of sRGB textures and framebuffers.\n"
 "    This option forces the options 'indirect' and 'gamma'.\n"
-"    NOTE: For YUV colorspaces, gamma 2.2 is assumed. RGB input is always\n"
+"    NOTE: For YUV colorspaces, gamma 1/0.45 is assumed. RGB input is always\n"
 "    assumed to be in sRGB.\n"
 "  pbo\n"
 "    Enable use of PBOs. This is faster, but can sometimes lead to\n"
diff --git a/video/out/vo_opengl_shaders.glsl b/video/out/vo_opengl_shaders.glsl
index 1f302889e4..13595ec77e 100644
--- a/video/out/vo_opengl_shaders.glsl
+++ b/video/out/vo_opengl_shaders.glsl
@@ -74,7 +74,7 @@ void main() {
 #ifdef USE_OSD_LINEAR_CONV
     // If no 3dlut is being used, we need to pull up to linear light for
     // the sRGB function. *IF* 3dlut is used, we do not.
-    color.rgb = pow(color.rgb, vec3(2.2));
+    color.rgb = pow(color.rgb, vec3(1.0/0.45));
 #endif
 #ifdef USE_OSD_3DLUT
     color = vec4(texture3D(lut_3d, color.rgb).rgb, color.a);
@@ -331,12 +331,12 @@ void main() {
     color = mat3(colormatrix) * color + colormatrix[3];
 #endif
 #ifdef USE_LINEAR_CONV
-    color = pow(color, vec3(2.2));
+    color = pow(color, vec3(1.0/0.45));
 #endif
 #ifdef USE_LINEAR_CONV_INV
     // Convert from linear RGB to gamma RGB before putting it through the 3D-LUT
     // in the final stage.
-    color = pow(color, vec3(1.0/2.2));
+    color = pow(color, vec3(0.45));
 #endif
 #ifdef USE_GAMMA_POW
     color = pow(color, inv_gamma);