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vo_opengl: Add :icc-approx-gamma suboption to approximate BT.709 gamma 

This uses the value of 1.95 as an approximation for the exact gamma
curve, which replicates the behavior of popular video software including
anything in the Apple ecosystem, as per issue #534.
This commit is contained in:
Niklas Haas 2014-02-24 13:39:39 +01:00
parent e3f7d4f5ea
commit 701c8c8254
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GPG Key ID: 3BA77D4BFDB10BCE
3 changed files with 24 additions and 5 deletions
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8
DOCS/man/en/vo.rst
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@ -462,6 +462,14 @@ Available video output drivers are:
3
absolute colorimetric (default)
``icc-approx-gamma``
Approximate the actual BT.709 gamma function as a pure power curve of
1.95. This is not quite correct, but it was historically used as a
faster version of the actual function, and seems to still be used by
many video editing programs and perhaps even studios. If you find your
videos displaying ever so slightly slightly brighter than you'd expect
them to, try enabling this option.
``3dlut-size=<r>x<g>x<b>``
Size of the 3D LUT generated from the ICC profile in each dimension.
Default is 128x256x64.

20
video/out/gl_lcms.c
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@ -73,6 +73,7 @@ const struct m_sub_options mp_icc_conf = {
OPT_STRING("icc-profile", profile, 0),
OPT_STRING("icc-cache", cache, 0),
OPT_INT("icc-intent", intent, 0),
OPT_FLAG("icc-approx-gamma", approx, 0),
OPT_STRING_VALIDATE("3dlut-size", size_str, 0, validate_3dlut_size_opt),
{0}
},
@ -164,13 +165,22 @@ struct lut3d *mp_load_icc(struct mp_icc_opts *opts, struct mp_log *log,
.Blue = {0.15, 0.06, 1.0},
};
/* Rec BT.709 defines the tone curve as:
V = 1.099 * L^0.45 - 0.099 for L >= 0.018
V = 4.500 * L for L < 0.018
cmsToneCurve *tonecurve;
if (opts->approx) {
/* Apple's CMS, among other programs that rely on it, uses 1.95 as a
faster approximation of this curve. It's not quite correct, but the
option is provided for compatibility with such incorrect clips. */
tonecurve = cmsBuildGamma(NULL, 1.95);
} else {
/* Rec BT.709 defines the tone curve as:
V = 1.099 * L^0.45 - 0.099 for L >= 0.018
V = 4.500 * L for L < 0.018
The 0.081 parameter comes from inserting 0.018 into the function */
cmsToneCurve *tonecurve = cmsBuildParametricToneCurve(NULL, 4,
The 0.081 parameter comes from inserting 0.018 into the function */
tonecurve = cmsBuildParametricToneCurve(NULL, 4,
(cmsFloat64Number[5]){1/0.45, 1/1.099, 0.099/1.099, 1/4.5, 0.081});
}
cmsHPROFILE vid_profile = cmsCreateRGBProfile(&d65, &bt709prim,
(cmsToneCurve*[3]){tonecurve, tonecurve, tonecurve});
cmsFreeToneCurve(tonecurve);

1
video/out/gl_lcms.h
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@ -8,6 +8,7 @@ struct mp_icc_opts {
char *cache;
char *size_str;
int intent;
int approx;
};
struct lut3d;