[css-color-hdr] dded color-hdr function. Added ISO 21496-1 informative reference #11616

Author: svgeesus

css-color-hdr-1/Overview.bs

@@ -38,14 +38,19 @@ WPT Display: open
 			"href": "https://www.arib.or.jp/english/html/overview/doc/2-STD-B67v1_0.pdf",
 			"title": "Essential Parameter Values for the Extended Image Dynamic Range Television (EIDRTV) System for Programme Production",
 			"publisher": "ARIB",
-			"ate": "3 July 2015"
+			"date": "3 July 2015"
 		},
 		"DisplayHDR": {
 			"title": "Summary of DisplayHDR Specs under CTS 1.2",
 			"href": "https://displayhdr.org/performance-criteria/",
 			"publisher": "VESA",
 			"date": "17 May 2024"
 		},
+		"ISO 21496-1": {
+			"title": "Gain map metadata for image conversion: Part 1: Dynamic Range Conversion",
+			"href": "https://www.iso.org/standard/86775.html",
+			"publisher": "ISO"
+		},
 		"Perrin": {
 			"authors": [
 				"Perrin, A-F.",
@@ -450,6 +455,30 @@ Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynami
 	</pre>
 	</div>
 
+<h2 id="hdr-color-function">HDR colors parameterized by headroom: the ''hdr-color()'' function</h2>
+
+	The ''hdr-color()'' function allows a range of colors to be specified, 
+	whose value is automatically calculated based on the [=HDR headroom=].
+
+	It does this by specifying two <<color>> values, 
+	each with an associated level of HDR headroom.
+	The actual value is computed by interpolating between these two colors,
+	based on the current amount of HDR headroom.
+
+	This is a similar meachanism to gain maps, 
+	in raster images conforming to [[?ISO 21496-1]].
+	
+	The actual calculated result is not exposed, 
+	nor is the actual HDR headroom,
+	as this is a fingerprinting vector.
+
+	Its syntax is as follows:
+
+	<pre class='prod'>
+		<dfn>hdr-color()</dfn> = color-hdr([ <<color>> && <<number [1,infty]>>? ]#{2})
+	</pre>
+
+
 <h2 id="color-function">
 	Specifying Predefined and Custom Color Spaces: the ''color()'' Function
 </h2>