[css-color-4] list steps to interconvert predefined RGB spaces

Author: svgeesus

css-color-4/Overview.bs

@@ -3643,7 +3643,7 @@ Converting predefined color spaces to Lab</h4>
 
 	<!-- make these steps links to the appropriate section in a calculations appendix -->
 	<ol>
-		<li>Convert from gamma-corrected RGB to linear-light RGB (undo gamma encoding)
+		<li>Convert from gamma-encoded RGB to linear-light RGB (undo gamma encoding)
 		<li>Convert from linear RGB to CIE XYZ
 		<li>Convert from a D65 whitepoint (used by sRGB, ''display-p3'', ''a98-rgb'' and ''rec2020'') to the D50 whitepoint used in Lab,
 			with the Bradford transform. ''prophoto-rgb''' already has a D50 whitepoint.
@@ -3669,6 +3669,26 @@ Converting Lab to predefined color spaces</h4>
 	(for example, using an ICC profile with relative colorimetric rendering intent)
 	provided the results are the same for colors inside both the source and destination gamuts.
 
+<h4 id="predefined-to-predefined">
+	Converting between predefined RGB color spaces
+</h4>
+
+	Conversion from one predefined RGB colorspace to another
+	requires multiple steps,
+	one of which is only used when the whitepoints differ.
+	To convert from <em>src</em> to <em>dest</em>:
+
+	<ol>
+		<li>Convert from gamma-encoded <em>src</em>RGB to linear-light <em>src</em>RGB (undo gamma encoding)
+			<li>Convert from linear RGB to CIE XYZ
+		<li>If <em>src</em> and <em>dest</em> have different whitepoints,
+			convert the XYZ value from <em>src</em>White to <em>dest</em>White
+			with the Bradford transform.
+		</li>
+		<li>Convert from CIE XYZ to linear <em>dest</em>RGB
+		<li>Convert from linear-light <em>dest</em>RGB to <em>dest</em>RGB (do gamma encoding)
+	</ol>
+
 <h3 id="at-profile">
 Specifying a color profile: the ''@color-profile'' at-rule</h3>