add rec.2020 utilities

Author: Chris Lilley

css-color-4/utilities.js

@@ -45,6 +45,18 @@ function P3_to_LCH(RGB) {
 
     return Lab_to_LCH(XYZ_to_Lab(D65_to_D50(lin_P3_to_XYZ(lin_P3(RGB)))));
 }
+
+function 2020_to_LCH(RGB) {
+    // convert an array of gamma-corrected rec.2020 values
+    // in the 0.0 to 1.0 range
+    // to linear-light sRGB, then to CIE XYZ,
+    // then adapt from D65 to D50,
+    // then convert XYZ to CIE Lab
+    // and finally, convert to CIE LCH
+
+    return Lab_to_LCH(XYZ_to_Lab(D65_to_D50(lin_2020_to_XYZ(lin_2020(RGB)))));
+}
+
 function LCH_to_sRGB(LCH) {
     // convert an array of CIE LCH values
     // to CIE Lab, and then to XYZ,
@@ -71,4 +83,18 @@ function LCH_to_P3(LCH) {
     // so check for that :)
 
     return gam_P3(XYZ_to_lin_P3(D50_to_D65(Lab_to_XYZ(LCH_to_Lab(LCH)))));
+}
+
+function LCH_to_2020(LCH) {
+    // convert an array of CIE LCH values
+    // to CIE Lab, and then to XYZ,
+    // adapt from D50 to D65,
+    // then convert XYZ to linear-light rec.2020
+    // and finally to gamma corrected rec.2020
+    // for in-gamut colors, components are in the 0.0 to 1.0 range
+    // out of gamut colors may have negative components
+    // or components greater than 1.0
+    // so check for that :)
+
+    return gam_2020(XYZ_to_lin_2020(D50_to_D65(Lab_to_XYZ(LCH_to_Lab(LCH)))));
 }