[css-color-hdr] Define serialization, bit depths

Author: svgeesus

css-color-hdr/Overview.bs

@@ -185,48 +185,48 @@ Introducing Headroom {#introducing-headroom}
 The 'dynamic-range-limit' property {#the-dynamic-range-limit-property}
 -------------------------------
 
-		<pre class='propdef'>
-			Name: dynamic-range-limit
-			Value: standard | high | constrained-high
-			Initial: high
-			Applies to: all elements
-			Inherited: no
-			Percentages: n/a
-			Computed value: specified value
-			Animation type: by computed value type 
-			Canonical order: per grammar
+	<pre class='propdef'>
+		Name: dynamic-range-limit
+		Value: standard | high | constrained-high
+		Initial: high
+		Applies to: all elements
+		Inherited: no
+		Percentages: n/a
+		Computed value: specified value
+		Animation type: by computed value type 
+		Canonical order: per grammar
+	</pre>
+
+	<dl dfn-type="value" dfn-for="dynamic-range-limit">
+		<dt><dfn>standard</dfn>
+		<dd>
+			The highest luminance color
+			that is displayed is the same as '
+			media white, i.e. the CSS color ''white''.
+		</dd>
+		<dt><dfn>high</dfn>
+		<dd>
+			The highest peak luminance
+			that is displayed is much greater than
+			media white, i.e. the CSS color ''white'';
+			the precise level is not specified.
+		</dd>
+		<dt><dfn>constrained-high</dfn>
+		<dd>
+			The highest peak luminance
+			that is displayed is somewhat greater than
+			media white, i.e. the CSS color ''white'',
+			such that a mix of SDR and HDR content
+			can be comfortably viewed together.
+		</dd>	
+	</dl>
+
+	<div class="example" id="ex-hdr-limit-photogrid">
+		<pre class="lang-css">
+			body { dynamic-range-limit: standard; }
+			div.photogrid img { dynamic-range-limit: constrained-high }
 		</pre>
-	
-		<dl dfn-type="value" dfn-for="dynamic-range-limit">
-			<dt><dfn>standard</dfn>
-			<dd>
-				The highest luminance color
-				that is displayed is the same as '
-				media white, i.e. the CSS color ''white''.
-			</dd>
-			<dt><dfn>high</dfn>
-			<dd>
-				The highest peak luminance
-				that is displayed is much greater than
-				media white, i.e. the CSS color ''white'';
-				the precise level is not specified.
-			</dd>
-			<dt><dfn>constrained-high</dfn>
-			<dd>
-				The highest peak luminance
-				that is displayed is somewhat greater than
-				media white, i.e. the CSS color ''white'',
-				such that a mix of SDR and HDR content
-				can be comfortably viewed together.
-			</dd>	
-		</dl>
-
-		<div class="example" id="ex-hdr-limit-photogrid">
-			<pre class="lang-css">
-				body { dynamic-range-limit: standard; }
-				div.photogrid img { dynamic-range-limit: constrained-high }
-			</pre>
-		</div>
+	</div>
 
 Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynamic-range-limit-mix}
 --------------------------------------------------------
@@ -291,14 +291,6 @@ Predefined color spaces for HDR: {#predefined-HDR}
 	with each having a valid range of [0, 1]
 	regardless of the actual bit depth (10 or 12 bits per component).
 
-	Issue: should this specification recommend that the CSS Object Model
-	store these values in the 16-bit half-floating point representation
-	(IEEE standard 754-2008.)
-	from BT.2100 pp. 9-10? (or any wider representation, like float or double)?
-
-	Issue: should the values accept % as well as number? so 19% as well as 0.19.
-	Probably yes.
-
 	The Perceptual Quantizer (PQ) electro-optical transfer function is used
 	[[SMPTE-ST-2084]],[[!Rec_BT.2100]].
 	PQ assumes a reference viewing condition
@@ -741,6 +733,59 @@ However, implementations may chose to incorporate
 a color re-rendering step (OOTF)
 to account for non-reference viewing conditions.
 
+<!--
+ ██████  ████████ ████████  ████    ███    ██
+██    ██ ██       ██     ██  ██    ██ ██   ██
+██       ██       ██     ██  ██   ██   ██  ██
+ ██████  ██████   ████████   ██  ██     ██ ██
+      ██ ██       ██   ██    ██  █████████ ██
+██    ██ ██       ██    ██   ██  ██     ██ ██
+ ██████  ████████ ██     ██ ████ ██     ██ ████████
+-->
+
+<h2 id='serializing-color-values'>
+Serializing <<color>> Values</h2>
+
+<h3 id="serializing-color-function-values">
+Serializing values of the ''color()'' function</h3>
+
+	This section extends [[css-color-4#serializing-color-function-values]]
+	
+	The serialized form of ''color()'' values
+	is derived from the [=computed value=]
+	and uses the ''color()'' form,
+	with <a href="https://infra.spec.whatwg.org/#ascii-lowercase">ASCII lowercase</a> 
+	letters for the function name
+	and the color space name.
+
+	The component values are serialized in base 10,
+	as <<number>>.
+	A single ASCII space character " "
+	must be used as the separator
+	between the component values,
+	and also between the color space name and the first color component.
+
+	For the predefined HDR color spaces,
+	the <em>minimum</em> precision for round-tripping is as follows:
+
+	<table class="data" id="predefined-precision-table">
+		<tr><th>HDR color space</th><th>Minimum bits</th></tr>
+		<tr>
+			<td>''rec2100-pq'', ''rec2100-hlg''</td>
+			<td>10</td>
+			<!-- to conform to BT.2100 which recommends 12 but allows 10 -->
+		</tr>
+		<tr>
+			<td>''rec2100-linear'', ''jzazbz'', ''jzczhz'', ''ictcp''</td>
+			<td>16</td>
+		</tr>
+	</table>
+
+	(16bit, half-float, or float <em>per component</em>
+	is recommended for internal storage).
+	Values must be <a href="https://drafts.csswg.org/css-values-4/#combine-integers">rounded towards +∞</a>, not truncated.
+
+
 
 <!-- Sample section {#sample-topic}
 ==============================