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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.
This commit is contained in:
nand 2012-12-23 19:49:19 +01:00 committed by wm4
parent 6be50fa773
commit b32f2ef0d3
3 changed files with 7 additions and 7 deletions
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4
DOCS/man/en/vo.rst
View File

@ -325,8 +325,8 @@ opengl
Enable gamma-correct scaling by working in linear light. This
makes use of sRGB textures and framebuffers.
This option forces the options 'indirect' and 'gamma'.
NOTE: for YUV colorspaces, gamma 2.2 is assumed. RGB input is always
assumed to be in sRGB.
NOTE: for YUV colorspaces, gamma 1/0.45 (2.222) is assumed. RGB input
is always assumed to be in sRGB.
This option is not really useful, as gamma-correct scaling has not much
influence on typical video playback. Most visible effect comes from
slightly different gamma.

4
video/out/vo_opengl.c
View File

@ -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"

6
video/out/vo_opengl_shaders.glsl
View File

@ -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);