finish off the sRGB - LCH utilities

Author: svgeesus

css-color-4/utilities.js

@@ -20,7 +20,7 @@ function contrast(RGB1, RGB2) {
     var L1 = sRGB_to_luminance(RGB1);
     var L2 = sRGB_to_luminance(RGB2);
 
-    if L1 > L2 return (L1 + 0.05) / (L2 + 0.05);
+    if (L1 > L2) return (L1 + 0.05) / (L2 + 0.05);
     return (L2 + 0.05) / (L1 + 0.05);
 }
 
@@ -32,5 +32,19 @@ function sRGB_to_LCH(RGB) {
     // then convert XYZ to CIE Lab
     // and finally, convert to CIE LCH
 
-    return lin_sRGB_to_XYZ(lin_sRGB(RGB));
+    return Lab_to_LCH(XYZ_to_Lab(D65_to_D50(lin_sRGB_to_XYZ(lin_sRGB(RGB)))));
+}
+
+functions LCH_to_sRGB(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 sRGB
+    // and finally to gamma corrected sRGB
+    // 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(sRGB(XYZ_to_lin_sRGB(Lab_to_XYZ(D50_to_D65(LCH_to_Lab(LCH)))));
 }

css-color-5/Overview.bs

@@ -71,9 +71,9 @@ Mixing colors: the ''color-mix'' function {#colormix}
 
 <div class="example">
 	This example produces the mixture of red and yellow,
-	in ''lch'' colorspace (the default),
+	in ''lch()'' colorspace (the default),
 	with the lightness being 30% of the lightness of red
-	and 70% of the lightness of yellow.
+	(and thus, 70% of the lightness of yellow).
 	The chroma and hue of red are left unchanged.
 
 	<pre class="lang-css">mix-color(red, yellow, lightness(30%));</pre>
@@ -84,6 +84,8 @@ Mixing colors: the ''color-mix'' function {#colormix}
 	  * mix lightness is 54.2917 * 0.3 + 97.6071 * 0.7 = 84.6125
 	  * mixed result is lch(84.6125 106.8390 40.8526)
 	  * which is a very light red (and outside the gamut of sRGB: rgb(140.4967% 51.2654% 32.6891%))
+
+	<!-- Maybe the first example should reslve to an in-gamut color; show out of gamut colors later? -->
 </div>
 
 Instead of a list of color functions,