[cs-color-hdr] PQ and HLG media whites, composting

Author: svgeesus

css-color-hdr/Overview.bs

@@ -20,6 +20,12 @@ Abstract: This module explores additions to CSS Color 4 to enable High Dynamic R
 			"date": "3 July 2015",
 			"rawDate": "2015-07-03"
 		},
+		"Dolby-PQ-levels": {
+			"href": "https://www.dolby.com/us/en/technologies/dolby-vision/operational-guidelines-for-pq-2.pdf",
+			"title": "Reference Level Guidelines for PQ (BT.2100)",
+			"publisher": "Dolby Laoratories, Inc.",
+			"date": "2016"
+		},
 		"Rec.2100": {
 			"href": "https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.2100-2-201807-I!!PDF-E.pdf",
 			"title": "ITU-R  BT.2100-2 Image parameter values for high dynamic range television for use in production and international programme exchange",
@@ -114,15 +120,17 @@ Predefined colorspaces for HDR: {#predefined-HDR}
 	(IEEE standard 754-2008.)
 	from BT.2100 pp. 9-10? (or any wider representation, like float or double)?
 
-	Issue: should the range be in absolute nits, ie [0.0, 10,000]?
+	Issue: should the range be in absolute nits, ie [0.0, 10,000]? Probably not.
+
+	Issue: should th values acept % as wel as number? so 19% as well as 0.19.
 
 	The Perceptual Quantizer (PQ) electro-optical transfer function is used
 	[[SMPTE-ST-2084]],[[!Rec.2100]].
 
 	ITU Reference 2100 is used for HDR 4k and 8k television.
 
 	In contrast to SDR colorspaces and some HDR colorspaces,
-	the values are absolute rather than relative.
+	the values are <em>absolute</em> rather than relative.
 
 	Issue: add a diagram showing SDR and HDR dynamic ranges on a log scale
 
@@ -136,6 +144,7 @@ Predefined colorspaces for HDR: {#predefined-HDR}
 		<tr><th>Blue chromaticity</th><td>0.131</td><td>0.046</td></tr>
 		<tr><th>White chromaticity</th><td>0.3127</td><td>0.3290</td></tr>
 		<tr><th>Transfer function</th><td colspan="2">Perceptual Quantizer</td></tr>
+		<tr><th>White luminance</th></tr><td colspan="2">140 cd/m² [[!Dolby-PQ-levels]]</td></tr>
 		<tr><th>Peak white luminance</th><td colspan="2">10,000 cd/m²</td></tr>
 		<tr><th>Black luminance</th><td colspan="2">0.001 cd/m²</td></tr>
 	</table>
@@ -239,6 +248,7 @@ Predefined colorspaces for HDR: {#predefined-HDR}
 		<tr><th>Blue chromaticity</th><td>0.131</td><td>0.046</td></tr>
 		<tr><th>White chromaticity</th><td>0.3127</td><td>0.3290</td></tr>
 		<tr><th>Transfer function</th><td colspan="2">Hybrid log Gamma</td></tr>
+		<tr><th>White luminance</th></tr><td colspan="2">depends on viewing conditions</td></tr>
 		<tr><th>Peak white luminance</th><td colspan="2">12 times reference white</td></tr>
 		<tr><th>Black luminance</th><td colspan="2">depends on reference white, see text</td></tr>
 	</table>
@@ -367,6 +377,32 @@ Converting JzCzHz colors to Jzazbz  colors</h4>
 			<li>Jz is the same
 		</ol>
 
+Compositing SDR and HDR content {#Compositing-SDR-HDR}
+===============================
+
+Compositing should take place in CE XYZ,
+as it is a linear-light space witout gamut limitations.
+Implementations may chose to composite in a linear-light RGB space instead,
+wich will give the same result
+provided out-fgamut values (negative, or greater than 100%)
+are corectly handled
+and not clipped orgamut mapped until
+the final transfer to the device colorspace.
+
+Relative HDR using the HLG transfer function
+must map SDR media white
+to the same luminance as is used
+to display the 75% HLG value.
+
+Absolute HDR using the PQ transfer function
+should map SDR media white
+to 140 cd/m², the same luminance as is used
+to display the 54% PQ value.
+However, implementations may chose to incorporate
+a color re-rendering step (OOTF)
+to acount for non-reference viewing conditions.
+
+
 <!-- Sample section {#sample-topic}
 ==============================