video: Add BT.2020-NCL colorspace and transfer function

Source: http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.2020-0-201208-I!!PDF-E.pdf

DOCS/man/options.rst

@@ -537,6 +537,7 @@ OPTIONS
     :auto:          automatic selection (default)
     :BT.601:        ITU-R BT.601 (SD)
     :BT.709:        ITU-R BT.709 (HD)
+    :BT.2020-NC:    ITU-R BT.2020 non-constant luminance system
     :SMPTE-240M:    SMPTE-240M
 
 ``--colormatrix-input-range=<color-range>``

DOCS/man/vo.rst

@@ -509,7 +509,7 @@ Available video output drivers are:
             absolute colorimetric
 
     ``approx-gamma``
-        Approximate the actual BT.709 gamma function as a pure power curve of
+        Approximate the actual gamma function as a pure power curve of
         1.95. A number of video editing programs and studios apparently use this
         for mastering instead of the true curve. Most notably, anything in the
         Apple ecosystem uses this approximation - including all programs

old-configure

@@ -797,6 +797,12 @@ api_statement_check \
     libavcodec/avcodec.h \
     'int x, y; avcodec_enum_to_chroma_pos(&x, &y, AVCHROMA_LOC_UNSPECIFIED)'
 
+api_statement_check \
+    "libavcodec avcol_spc_bt2020 available" \
+    HAVE_AVCOL_SPC_BT2020 \
+    libavcodec/avcodec.h \
+    'int x = AVCOL_SPC_BT2020_NCL'
+
 api_statement_check \
     "libavcodec metadata update side data" \
     HAVE_AVCODEC_METADATA_UPDATE_SIDE_DATA \

options/options.c

@@ -389,6 +389,7 @@ const m_option_t mp_opts[] = {
                 {"BT.601", MP_CSP_BT_601},
                 {"BT.709", MP_CSP_BT_709},
                 {"SMPTE-240M", MP_CSP_SMPTE_240M},
+                {"BT.2020-NC", MP_CSP_BT_2020_NC},
                 {"YCgCo", MP_CSP_YCGCO})),
     OPT_CHOICE("colormatrix-input-range", requested_input_range, 0,
                ({"auto", MP_CSP_LEVELS_AUTO},

video/csputils.c

@@ -27,6 +27,8 @@
  * version 2.1 of the License, or (at your option) any later version.
  */
 
+#include "config.h"
+
 #include <stdint.h>
 #include <math.h>
 #include <assert.h>
@@ -40,6 +42,7 @@ const char *const mp_csp_names[MP_CSP_COUNT] = {
     "BT.601 (SD)",
     "BT.709 (HD)",
     "SMPTE-240M",
+    "BT.2020 (NC)",
     "RGB",
     "XYZ",
     "YCgCo",
@@ -70,6 +73,9 @@ enum mp_csp avcol_spc_to_mp_csp(int avcolorspace)
     switch (avcolorspace) {
         case AVCOL_SPC_BT709:      return MP_CSP_BT_709;
         case AVCOL_SPC_BT470BG:    return MP_CSP_BT_601;
+#if HAVE_AVCOL_SPC_BT2020
+        case AVCOL_SPC_BT2020_NCL: return MP_CSP_BT_2020_NC;
+#endif
         case AVCOL_SPC_SMPTE170M:  return MP_CSP_BT_601;
         case AVCOL_SPC_SMPTE240M:  return MP_CSP_SMPTE_240M;
         case AVCOL_SPC_RGB:        return MP_CSP_RGB;
@@ -92,6 +98,9 @@ int mp_csp_to_avcol_spc(enum mp_csp colorspace)
     switch (colorspace) {
         case MP_CSP_BT_709:     return AVCOL_SPC_BT709;
         case MP_CSP_BT_601:     return AVCOL_SPC_BT470BG;
+#if HAVE_AVCOL_SPC_BT2020
+        case MP_CSP_BT_2020_NC: return AVCOL_SPC_BT2020_NCL;
+#endif
         case MP_CSP_SMPTE_240M: return AVCOL_SPC_SMPTE240M;
         case MP_CSP_RGB:        return AVCOL_SPC_RGB;
         case MP_CSP_YCGCO:      return AVCOL_SPC_YCOCG;
@@ -218,6 +227,7 @@ void mp_get_yuv2rgb_coeffs(struct mp_csp_params *params, float m[3][4])
     case MP_CSP_BT_601:     luma_coeffs(m, 0.299,  0.587,  0.114 ); break;
     case MP_CSP_BT_709:     luma_coeffs(m, 0.2126, 0.7152, 0.0722); break;
     case MP_CSP_SMPTE_240M: luma_coeffs(m, 0.2122, 0.7013, 0.0865); break;
+    case MP_CSP_BT_2020_NC: luma_coeffs(m, 0.2627, 0.6780, 0.0593); break;
     case MP_CSP_RGB: {
         static const float ident[3][4] = {{1, 0, 0}, {0, 1, 0}, {0, 0, 1}};
         memcpy(m, ident, sizeof(ident));

video/csputils.h

@@ -37,6 +37,7 @@ enum mp_csp {
     MP_CSP_BT_601,
     MP_CSP_BT_709,
     MP_CSP_SMPTE_240M,
+    MP_CSP_BT_2020_NC,
     MP_CSP_RGB,
     MP_CSP_XYZ,
     MP_CSP_YCGCO,

video/mp_image.c

@@ -521,6 +521,7 @@ void mp_image_params_guess_csp(struct mp_image_params *params)
     if (fmt.flags & MP_IMGFLAG_YUV) {
         if (params->colorspace != MP_CSP_BT_601 &&
             params->colorspace != MP_CSP_BT_709 &&
+            params->colorspace != MP_CSP_BT_2020_NC &&
             params->colorspace != MP_CSP_SMPTE_240M &&
             params->colorspace != MP_CSP_YCGCO)
         {

video/out/gl_video_shaders.glsl

@@ -49,10 +49,10 @@ vec3 srgb_compand(vec3 v)
                lessThanEqual(vec3(0.0031308), v));
 }
 
-vec3 bt709_expand(vec3 v)
+vec3 bt2020_expand(vec3 v)
 {
-    return mix(v / 4.5, pow((v + vec3(0.099))/1.099, vec3(1/0.45)),
+    return mix(v / 4.5, pow((v + vec3(0.0993))/1.0993, vec3(1/0.45)),
-               lessThanEqual(vec3(0.0812), v));
+               lessThanEqual(vec3(0.08145), v));
 }
 #endif
 
@@ -85,8 +85,8 @@ void main() {
     // Although we are not scaling in linear light, both 3DLUT and SRGB still
     // operate on linear light inputs so we have to convert to it before
     // either step can be applied.
-    color.rgb = bt709_expand(color.rgb);
+    color.rgb = bt2020_expand(color.rgb);
-    // NOTE: This always applies the true BT709, maybe we need to use
+    // NOTE: This always applies the true BT2020, maybe we need to use
     // approx-gamma here too?
 #endif
 #ifdef USE_OSD_3DLUT
@@ -387,13 +387,18 @@ void main() {
 #endif
 #ifdef USE_LINEAR_LIGHT
     // If we are scaling in linear light (SRGB or 3DLUT option enabled), we
-    // expand our source colors before scaling
+    // expand our source colors before scaling. This shader currently just
+    // assumes everything uses the BT.2020 12-bit gamma function, since the
+    // difference between this and BT.601, BT.709 and BT.2020 10-bit is well
+    // below the rounding error threshold for both 8-bit and even 10-bit
+    // content. It only makes a difference for 12-bit sources, so it should be
+    // fine to use here.
 #ifdef USE_APPROX_GAMMA
-    // We differentiate between approximate BT.709 (gamma 1.95) ...
+    // We differentiate between approximate BT.2020 (gamma 1.95) ...
     color = pow(color, vec3(1.95));
 #else
-    // ... and actual BT709 (two-part function)
+    // ... and actual BT.2020 (two-part function)
-    color = bt709_expand(color);
+    color = bt2020_expand(color);
 #endif
 #endif
     // Image upscaling happens roughly here

wscript

@@ -364,6 +364,12 @@ Libav libraries ({0}). Aborting.".format(" ".join(libav_pkg_config_checks))
         'func': check_statement('libavcodec/avcodec.h', """int x, y;
             avcodec_enum_to_chroma_pos(&x, &y, AVCHROMA_LOC_UNSPECIFIED)""",
             use='libav')
+    }, {
+        'name': 'avcol-spc-bt2020',
+        'desc': 'libavcodec avcol_spc_bt2020 available',
+        'func': check_statement('libavcodec/avcodec.h',
+                                'int x = AVCOL_SPC_BT2020_NCL',
+                                use='libav')
     }, {
         'name': 'avutil-qp-api',
         'desc': 'libavutil QP API',