vo_opengl: generate 3DLUT against source and use full BT.1886

This commit refactors the 3DLUT loading mechanism to build the 3DLUT
against the original source characteristics of the file. This allows us,
among other things, to use a real BT.1886 profile for the source. This
also allows us to actually use perceptual mappings. Finally, this
reduces errors on standard gamut displays (where the previous 3DLUT
target of BT.2020 was unreasonably wide).

This also improves the overall accuracy of the 3DLUT due to eliminating
rounding errors where possible, and allows for more accurate use of
LUT-based ICC profiles.

The current code is somewhat more ugly than necessary, because the idea
was to implement this commit in a working state first, and then maybe
refactor the profile loading mechanism in a later commit.

Fixes #2815.

1 files changed, 98 insertions, 25 deletions

diff --git a/video/out/opengl/lcms.c b/video/out/opengl/lcms.c
index c956127a75..8f6b40830a 100644
--- a/video/out/opengl/lcms.c
+++ b/video/out/opengl/lcms.c
@@ -44,6 +44,8 @@ struct gl_lcms {
     size_t icc_size;
     char *icc_path;
     bool changed;
+    enum mp_csp_prim prev_prim;
+    enum mp_csp_trc prev_trc;
 
     struct mp_log *log;
     struct mpv_global *global;
@@ -166,16 +168,88 @@ void gl_lcms_set_memory_profile(struct gl_lcms *p, bstr *profile)
     p->icc_size = profile->len;
 }
 
-// Return and _reset_ whether the lookul table has changed since the last call.
-// If it has changed, gl_lcms_get_lut3d() should be called.
-bool gl_lcms_has_changed(struct gl_lcms *p)
+// Return and _reset_ whether the profile or config has changed since the last
+// call. If it has changed, gl_lcms_get_lut3d() should be called.
+bool gl_lcms_has_changed(struct gl_lcms *p, enum mp_csp_prim prim,
+                         enum mp_csp_trc trc)
 {
-    bool change = p->changed;
+    bool change = p->changed || p->prev_prim != prim || p->prev_trc != trc;
     p->changed = false;
+    p->prev_prim = prim;
+    p->prev_trc = trc;
     return change;
 }
 
-bool gl_lcms_get_lut3d(struct gl_lcms *p, struct lut3d **result_lut3d)
+static cmsHPROFILE get_vid_profile(cmsContext cms, cmsHPROFILE disp_profile,
+                                   enum mp_csp_prim prim, enum mp_csp_trc trc)
+{
+    // The input profile for the transformation is dependent on the video
+    // primaries and transfer characteristics
+    struct mp_csp_primaries csp = mp_get_csp_primaries(prim);
+    cmsCIExyY wp_xyY = {csp.white.x, csp.white.y, 1.0};
+    cmsCIExyYTRIPLE prim_xyY = {
+        .Red   = {csp.red.x,   csp.red.y,   1.0},
+        .Green = {csp.green.x, csp.green.y, 1.0},
+        .Blue  = {csp.blue.x,  csp.blue.y,  1.0},
+    };
+
+    cmsToneCurve *tonecurve = NULL;
+    switch (trc) {
+    case MP_CSP_TRC_LINEAR:  tonecurve = cmsBuildGamma(cms, 1.0); break;
+    case MP_CSP_TRC_GAMMA18: tonecurve = cmsBuildGamma(cms, 1.8); break;
+    case MP_CSP_TRC_GAMMA22: tonecurve = cmsBuildGamma(cms, 2.2); break;
+    case MP_CSP_TRC_GAMMA28: tonecurve = cmsBuildGamma(cms, 2.8); break;
+
+    case MP_CSP_TRC_SRGB:
+        // Values copied from Little-CMS
+        tonecurve = cmsBuildParametricToneCurve(cms, 4,
+                (double[5]){2.40, 1/1.055, 0.055/1.055, 1/12.92, 0.04045});
+        break;
+
+    case MP_CSP_TRC_PRO_PHOTO:
+        tonecurve = cmsBuildParametricToneCurve(cms, 4,
+                (double[5]){1.8, 1.0, 0.0, 1/16.0, 0.03125});
+        break;
+
+    case MP_CSP_TRC_BT_1886: {
+        // To build an appropriate BT.1886 transformation we need access to
+        // the display's black point, so we use the reverse mappings
+        cmsHPROFILE xyz_profile = cmsCreateXYZProfileTHR(cms);
+        cmsHTRANSFORM rgb2xyz = cmsCreateTransformTHR(cms,
+                disp_profile, TYPE_RGB_16, xyz_profile, TYPE_XYZ_DBL,
+                INTENT_RELATIVE_COLORIMETRIC, 0);
+        cmsCloseProfile(xyz_profile);
+        if (!rgb2xyz)
+            return false;
+
+        uint64_t black[3] = {0};
+        cmsCIEXYZ disp_black;
+        cmsDoTransform(rgb2xyz, black, &disp_black, 1);
+
+        // Build the parametric BT.1886 transfer curve
+        const double gamma = 2.40;
+        double binv = pow(disp_black.Y, 1.0/gamma);
+        tonecurve = cmsBuildParametricToneCurve(cms, 6,
+                (double[4]){gamma, 1.0 - binv, binv, 0.0});
+        break;
+    }
+
+    default:
+        abort();
+    }
+
+    if (!tonecurve)
+        return false;
+
+    cmsHPROFILE *vid_profile = cmsCreateRGBProfileTHR(cms, &wp_xyY, &prim_xyY,
+                (cmsToneCurve*[3]){tonecurve, tonecurve, tonecurve});
+    cmsFreeToneCurve(tonecurve);
+
+    return vid_profile;
+}
+
+bool gl_lcms_get_lut3d(struct gl_lcms *p, struct lut3d **result_lut3d,
+                       enum mp_csp_prim prim, enum mp_csp_trc trc)
 {
     int s_r, s_g, s_b;
     bool result = false;
@@ -197,8 +271,8 @@ bool gl_lcms_get_lut3d(struct gl_lcms *p, struct lut3d **result_lut3d)
         // because we may change the parameter in the future or make it
         // customizable, same for the primaries.
         char *cache_info = talloc_asprintf(tmp,
-                "ver=1.1, intent=%d, size=%dx%dx%d, gamma=2.4, prim=bt2020\n",
-                p->opts.intent, s_r, s_g, s_b);
+                "ver=1.2, intent=%d, size=%dx%dx%d, prim=%d, trc=%d\n",
+                p->opts.intent, s_r, s_g, s_b, prim, trc);
 
         uint8_t hash[32];
         struct AVSHA *sha = av_sha_alloc();
@@ -242,23 +316,12 @@ bool gl_lcms_get_lut3d(struct gl_lcms *p, struct lut3d **result_lut3d)
     if (!profile)
         goto error_exit;
 
-    // We always generate the 3DLUT against BT.2020, and transform into this
-    // space inside the shader if the source differs.
-    struct mp_csp_primaries csp = mp_get_csp_primaries(MP_CSP_PRIM_BT_2020);
-
-    cmsCIExyY wp = {csp.white.x, csp.white.y, 1.0};
-    cmsCIExyYTRIPLE prim = {
-        .Red   = {csp.red.x,   csp.red.y,   1.0},
-        .Green = {csp.green.x, csp.green.y, 1.0},
-        .Blue  = {csp.blue.x,  csp.blue.y,  1.0},
-    };
+    cmsHPROFILE vid_profile = get_vid_profile(cms, profile, prim, trc);
+    if (!vid_profile) {
+        cmsCloseProfile(profile);
+        goto error_exit;
+    }
 
-    // 2.4 is arbitrarily used as a gamma compression factor for the 3DLUT,
-    // reducing artifacts due to rounding errors on wide gamut profiles
-    cmsToneCurve *tonecurve = cmsBuildGamma(cms, 2.4);
-    cmsHPROFILE vid_profile = cmsCreateRGBProfileTHR(cms, &wp, &prim,
-                        (cmsToneCurve*[3]){tonecurve, tonecurve, tonecurve});
-    cmsFreeToneCurve(tonecurve);
     cmsHTRANSFORM trafo = cmsCreateTransformTHR(cms, vid_profile, TYPE_RGB_16,
                                                 profile, TYPE_RGB_16,
                                                 p->opts.intent,
@@ -333,7 +396,17 @@ struct gl_lcms *gl_lcms_init(void *talloc_ctx, struct mp_log *log,
 
 void gl_lcms_set_options(struct gl_lcms *p, struct mp_icc_opts *opts) { }
 void gl_lcms_set_memory_profile(struct gl_lcms *p, bstr *profile) { }
-bool gl_lcms_get_lut3d(struct gl_lcms *p, struct lut3d **x) { return false; }
-bool gl_lcms_has_changed(struct gl_lcms *p) { return false; }
+
+bool gl_lcms_has_changed(struct gl_lcms *p, enum mp_csp_prim prim,
+                         enum mp_csp_trc trc)
+{
+    return false;
+}
+
+bool gl_lcms_get_lut3d(struct gl_lcms *p, struct lut3d **result_lut3d,
+                       enum mp_csp_prim prim, enum mp_csp_trc trc)
+{
+    return false;
+}
 
 #endif