Release Movit 1.7.1.

[movit] / colorspace_conversion_effect.cpp

diff --git a/colorspace_conversion_effect.cpp b/colorspace_conversion_effect.cpp
index baced38fb9b6c03e6d1ca94d4b0a38a36d3c2d34..c14a8898f9ab2e10588479dc4601a37e34257ab4 100644 (file)
--- a/colorspace_conversion_effect.cpp
+++ b/colorspace_conversion_effect.cpp
@@ -1,12 +1,15 @@
 #include <assert.h>
-
+#include <Eigen/Core>
 #include <Eigen/LU>
 
 #include "colorspace_conversion_effect.h"
-#include "util.h"
 #include "d65.h"
+#include "util.h"
 
 using namespace Eigen;
+using namespace std;
+
+namespace movit {
 
 // Color coordinates from Rec. 709; sRGB uses the same primaries.
 static const double rec709_x_R = 0.640, rec709_x_G = 0.300, rec709_x_B = 0.150;
@@ -18,6 +21,10 @@ static const double rec601_525_y_R = 0.340, rec601_525_y_G = 0.595, rec601_525_y
 static const double rec601_625_x_R = 0.640, rec601_625_x_G = 0.290, rec601_625_x_B = 0.150;
 static const double rec601_625_y_R = 0.330, rec601_625_y_G = 0.600, rec601_625_y_B = 0.060;
 
+// Color coordinates from Rec. 2020.
+static const double rec2020_x_R = 0.708, rec2020_x_G = 0.170, rec2020_x_B = 0.131;
+static const double rec2020_y_R = 0.292, rec2020_y_G = 0.797, rec2020_y_B = 0.046;
+
 ColorspaceConversionEffect::ColorspaceConversionEffect()
        : source_space(COLORSPACE_sRGB),
          destination_space(COLORSPACE_sRGB)
@@ -26,17 +33,33 @@ ColorspaceConversionEffect::ColorspaceConversionEffect()
        register_int("destination_space", (int *)&destination_space);
 }
 
-Matrix3d get_xyz_matrix(Colorspace space)
+Matrix3d ColorspaceConversionEffect::get_xyz_matrix(Colorspace space)
 {
        if (space == COLORSPACE_XYZ) {
                return Matrix3d::Identity();
        }
+       if (space == COLORSPACE_sRGB) {
+               // sRGB is not defined by the color primaries, but by concrete
+               // forward and inverse matrices that are rounded-off versions
+               // of the Rec. 709 color space (see
+               // https://photosauce.net/blog/post/what-makes-srgb-a-special-color-space).
+               // We're not compliant with the inverse matrix, since we'd be
+               // too accurate (sRGB is specified for 8-bit only); however,
+               // results should be very close in practice (and even closer to
+               // scRGB's inverse matrix, which is a higher-accuracy inversion of
+               // the same forward matrix).
+               return Matrix3d{
+                       { 0.4124, 0.3576, 0.1805 },
+                       { 0.2126, 0.7152, 0.0722 },
+                       { 0.0193, 0.1192, 0.9505 }
+               };
+       }
 
        double x_R, x_G, x_B;
        double y_R, y_G, y_B;
 
        switch (space) {
-       case COLORSPACE_REC_709:  // And sRGB.
+       case COLORSPACE_REC_709:
                x_R = rec709_x_R; x_G = rec709_x_G; x_B = rec709_x_B;
                y_R = rec709_y_R; y_G = rec709_y_G; y_B = rec709_y_B;
                break;
@@ -48,6 +71,10 @@ Matrix3d get_xyz_matrix(Colorspace space)
                x_R = rec601_625_x_R; x_G = rec601_625_x_G; x_B = rec601_625_x_B;
                y_R = rec601_625_y_R; y_G = rec601_625_y_G; y_B = rec601_625_y_B;
                break;
+       case COLORSPACE_REC_2020:
+               x_R = rec2020_x_R; x_G = rec2020_x_G; x_B = rec2020_x_B;
+               y_R = rec2020_y_R; y_G = rec2020_y_G; y_B = rec2020_y_B;
+               break;
        default:
                assert(false);
        }
@@ -57,14 +84,6 @@ Matrix3d get_xyz_matrix(Colorspace space)
        double z_G = 1.0 - x_G - y_G;
        double z_B = 1.0 - x_B - y_B;
 
-       // Find the XYZ coordinates of D65 (white point for both Rec. 601 and 709),
-       // normalized so that Y=1.
-       Vector3d d65_XYZ(
-               d65_x / d65_y,
-               1.0,
-               d65_z / d65_y
-       );
-
        // We have, for each primary (example is with red):
        //
        //   X_R / (X_R + Y_R + Z_R) = x_R
@@ -73,8 +92,8 @@ Matrix3d get_xyz_matrix(Colorspace space)
        //
        // Some algebraic fiddling yields (unsurprisingly):
        //
-       //   X_R = (x_R / y_R) Y_R
-       //   Z_R = (z_R / y_R) Y_R
+       //   X_R = (x_R / y_R) Y_R   (so define k1 = x_R / y_R)
+       //   Z_R = (z_R / y_R) Y_R   (so define k4 = z_R / y_R)
        //
        // We also know that since RGB=(1,1,1) should give us the
        // D65 illuminant, we must have
@@ -83,8 +102,8 @@ Matrix3d get_xyz_matrix(Colorspace space)
        //   Y_R + Y_G + Y_B = D65_Y
        //   Z_R + Z_G + Z_B = D65_Z
        //
-       // But since we already know how to express Y and Z by
-       // some constant multiple of X, this reduces to
+       // But since we already know how to express X and Z by
+       // some constant multiple of Y, this reduces to
        //
        //   k1 Y_R + k2 Y_G + k3 Y_B = D65_X
        //      Y_R +    Y_G +    Y_B = D65_Y
@@ -105,6 +124,7 @@ Matrix3d get_xyz_matrix(Colorspace space)
        temp(2,1) = z_G / y_G;
        temp(2,2) = z_B / y_B;
 
+       Vector3d d65_XYZ(d65_X, d65_Y, d65_Z);
        Vector3d Y_RGB = temp.inverse() * d65_XYZ;
 
        // Now convert xyY -> XYZ.
@@ -125,7 +145,7 @@ Matrix3d get_xyz_matrix(Colorspace space)
        return m;
 }
 
-std::string ColorspaceConversionEffect::output_fragment_shader()
+string ColorspaceConversionEffect::output_fragment_shader()
 {
        // Create a matrix to convert from source space -> XYZ,
        // another matrix to convert from XYZ -> destination space,
@@ -140,3 +160,5 @@ std::string ColorspaceConversionEffect::output_fragment_shader()
        return output_glsl_mat3("PREFIX(conversion_matrix)", m) +
                read_file("colorspace_conversion_effect.frag");
 }
+
+}  // namespace movit