[css-color-4] Canonical D50, D65 fix w3c#6618

Author: svgeesus

css-color-4/Overview.bs

@@ -245,7 +245,7 @@ Value Definitions</h3>
 
 	<figure>
 		<img src="images/UCS-display-p3.svg"
-		width=500 height=500
+		width=500 height=464
 			alt="uv chromaticity diagram of the display-p3 colorspace">
 		<figcaption>A chromaticity diagram showing
 			(in solid colors) the ''display-p3'' colorspace
@@ -255,6 +255,57 @@ Value Definitions</h3>
 		</figcaption>
 	</figure>
 
+	RGB colorspaces are additive,
+	and their gamut is defined
+	by the chromaticities of the red, green and blue primaries,
+	plus the chromaticity of the <dfn export>white point</dfn>
+	(the color formed by all three primaries at full intensity).
+
+	Most colorspaces use one of a few
+	daylight-simulating [=white points=],
+	which are named by the color temperature
+	of the corresponding black-body radiator.
+	For example, [=D65=] is a daylight whitepoint
+	corresponding to a correlated color temperature
+	of 6500 Kelvin
+	(actually 6504,
+	because the value of Plank's constant has changed
+	since the color was originally defined).
+
+	To avoid cumulative round-trip errors,
+	it is important that the identical chromaticity values
+	are used consistently,
+	at all places in a calculation. Thus,
+	for maximum compatibility,
+	for this specification,
+	the following two standard
+	daylight-simulating [=white points=] are defined:
+
+	<table class="data">
+		<thead>
+			<tr>
+				<th>Name&nbsp;</th>
+				<th>x</th>
+				<th>y</th>
+				<th>CCT</th>
+			</tr>
+		</thead>
+		<tbody>
+			<tr>
+				<td><dfn export>D50</dfn></td>
+				<td>0.345700</td>
+				<td>0.358500</td>
+				<td>6503K</td>
+			</tr>
+			<tr>
+				<td><dfn export>D65</dfn></td>
+				<td>0.312700</td>
+				<td>0.329000</td>
+				<td>6504K</td>
+			</tr>
+		</tbody>
+	</table>
+
 
 	When the measured physical characteristics
 	(such as the <abbr title="measured color, irrespective of lightness">chromaticities</abbr> of the primary colors it uses,
@@ -2991,7 +3042,7 @@ Device-independent Colors: Lab and LCH</h2>
 
 	<!-- diagram here -->
 
-	The illuminant is D50 white, a standardized daylight spectrum with a color temperature of 5000K,
+	The illuminant is [=D50=] white, a standardized daylight spectrum with a color temperature of 5000K,
 	as reflected by a perfect diffuse reflector; it approximates the color of sunlight on a sunny day.
 	D50 is also the whitepoint used for the profile connection space in ICC color interconversion,
 	the whitepoint used in image editors which offer Lab editing,
@@ -3192,7 +3243,7 @@ Converting RGB colors to Lab colors</h3>
 			so that arithmetic operations on the values
 			give the correct results.
 		<li>Convert from linear sRGB to CIE XYZ
-		<li>Convert from a D65 whitepoint (used by sRGB) to the D50 whitepoint used
+		<li>Convert from a [=D65=] whitepoint (used by sRGB) to the [=D50=] whitepoint used
 			in Lab, with the Bradford transform [[!Bradford-CAT]]
 		<li>Convert D50-adapted XYZ to Lab
 	</ol>
@@ -3212,7 +3263,7 @@ Converting Lab colors to RGB colors</h3>
 
 	<ol>
 		<li>Convert Lab to (D50-adapted) XYZ
-		<li>Convert from a D50 whitepoint (used by Lab) to the D65 whitepoint used
+		<li>Convert from a [=D50=] whitepoint (used by Lab) to the [=D65=] whitepoint used
 			in display-p3, with the Bradford transform
 		<li>Convert from (D65-adapted) CIE XYZ to linear-light display-p3
 		<li>Convert from linear-light display-p3 to display-p3 (do gamma encoding)
@@ -3524,11 +3575,11 @@ and ''xyz''.</h3>
 			It has the following characteristics:
 
 			<table>
-				<thead><td></td><td>x</td><td>y</td><td>notes</td></thead>
+				<thead><td></td><td>x</td><td>y</td></thead>
 				<tr><th>Red chromaticity</th><td>0.640</td><td>0.330</td></tr>
 				<tr><th>Green chromaticity</th><td>0.300</td><td>0.600</td></tr>
 				<tr><th>Blue chromaticity</th><td>0.150</td><td>0.060</td></tr>
-				<tr><th>White chromaticity</th><td>0.31272</td><td>0.32903</td><td>(D65)</td></tr>
+				<tr><th>White chromaticity</th> <td  colspan="2">[=D65=]</td></tr>
 				<tr><th>Transfer function</th><td colspan="2">see below</td></tr>
 				<tr><th>White luminance</th><td colspan="2">80.0 cd/m<sup>2</sup></td></tr>
 				<tr><th>Black luminance</th><td colspan="2">0.80 cd/m<sup>2</sup></td></tr>
@@ -3570,7 +3621,7 @@ and ''xyz''.</h3>
 			representing the red, green, and blue channels of the color,
 			with each having a valid range of [0, 1].
 			It uses the same primary chromaticities as [[!DCI-P3]],
-			but with a D65 whitepoint, and the same transfer curve as sRGB.
+			but with a [=D65=] whitepoint, and the same transfer curve as sRGB.
 
 			Modern displays, TVs, laptop screens and phone screens
 			are able to display all, or nearly all,
@@ -3579,11 +3630,11 @@ and ''xyz''.</h3>
 			It has the following characteristics:
 
 			<table>
-				<thead><td></td><td>x</td><td>y</td><td>notes</td></thead>
+				<thead><td></td><td>x</td><td>y</td></thead>
 				<tr><th>Red chromaticity</th><td>0.680</td><td>0.320</td></tr>
 				<tr><th>Green chromaticity</th><td>0.265</td><td>0.690</td></tr>
 				<tr><th>Blue chromaticity</th><td>0.150</td><td>0.060</td></tr>
-				<tr><th>White chromaticity</th><td>0.31272</td><td>0.32903</td><td>(D65)</td></tr>
+				<tr><th>White chromaticity</th> <td  colspan="2">[=D65=]</td></tr>
 				<tr><th>Transfer function</th><td colspan="2">same as srgb</td></tr>
 				<tr><th>White luminance</th><td colspan="2">80.0 cd/m<sup>2</sup></td></tr>
 				<tr><th>Black luminance</th><td colspan="2">0.80 cd/m<sup>2</sup></td></tr>
@@ -3622,11 +3673,11 @@ and ''xyz''.</h3>
 			It has the following characteristics:
 
 			<table>
-				<thead><td></td><td>x</td><td>y</td><td>notes</td></thead>
+				<thead><td></td><td>x</td><td>y</td></thead>
 				<tr><th>Red chromaticity</th><td>0.6400</td><td>0.3300</td></tr>
 				<tr><th>Green chromaticity</th><td>0.2100</td><td>0.7100</td></tr>
 				<tr><th>Blue chromaticity</th><td>0.1500</td><td>0.0600</td></tr>
-				<tr><th>White chromaticity</th><td>0.31272</td><td>0.32903</td><td>(D65)</td></tr>
+				<tr><th>White chromaticity</th> <td  colspan="2">[=D65=]</td></tr>
 				<tr><th>Transfer function</th><td colspan="2">256/563 </td></tr>
 				<tr><th>White luminance</th><td colspan="2">160.0 cd/m<sup>2</sup></td></tr>
 				<tr><th>Black luminance</th><td colspan="2">0.5557 cd/m<sup>2</sup></td></tr>
@@ -3666,7 +3717,7 @@ and ''xyz''.</h3>
 				with each having a valid range of [0, 1]. The transfer curve is
 				a gamma function with a value of 1/1.8,
 				and a small linear portion near black.
-				The white point is D50, the same as is used by CIE Lab. Thus,
+				The white point is [=D50=], the same as is used by CIE Lab. Thus,
 				conversion to Lab does not require the chromatic adaptation step.
 
 				The ProPhoto RGB space uses hyper-saturated,
@@ -3687,11 +3738,11 @@ and ''xyz''.</h3>
 				It has the following characteristics:
 
 				<table>
-					<thead><td></td><td>x</td><td>y</td><td>notes</td></thead>
+					<thead><td></td><td>x</td><td>y</td></thead>
 					<tr><th>Red chromaticity</th><td>0.734699</td><td>0.265301</td></tr>
 					<tr><th>Green chromaticity</th><td>0.159597</td><td>0.840403</td></tr>
 					<tr><th>Blue chromaticity</th><td>0.036598</td><td>0.000105</td></tr>
-					<tr><th>White chromaticity</th><td>0.345704</td><td>0.358540</td><td>(D50)</td></tr>
+					<tr><th>White chromaticity</th><td  colspan="2">[=D50=]</td></tr>
 					<tr><th>Transfer function</th><td colspan="2">see below </td></tr>
 					<tr><th>White luminance</th><td colspan="2">160.0 to 640.0 cd/m<sup>2</sup></td></tr>
 					<tr><th>Black luminance</th><td colspan="2">See text</td></tr>
@@ -3756,11 +3807,11 @@ and ''xyz''.</h3>
 			It has the following characteristics:
 
 			<table>
-				<thead><td></td><td>x</td><td>y</td><td>notes</td></thead>
+				<thead><td></td><td>x</td><td>y</td></thead>
 				<tr><th>Red chromaticity</th><td>0.708</td><td>0.292</td></tr>
 				<tr><th>Green chromaticity</th><td>0.170</td><td>0.797</td></tr>
 				<tr><th>Blue chromaticity</th><td>0.131</td><td>0.046</td></tr>
-				<tr><th>White chromaticity</th><td>0.31272</td><td>0.32903</td><td>(D65)</td></tr>
+				<tr><th>White chromaticity</th> <td  colspan="2">[=D65=]</td></tr>
 				<tr><th>Transfer function</th><td colspan="2">see below, from [[!Rec.2020]] table 4</td></tr>
 				<tr><th>Image state</th><td colspan="2">display-referred</td></tr>
 				<tr>
@@ -3812,7 +3863,7 @@ and ''xyz''.</h3>
 				representing the X,Y and Z values.
 				It represents the CIE XYZ color space,
 				scaled such that diffuse white has a luminance (Y) of 1.0
-				and, if necessary, chromatically adapted to a D50 reference white.
+				and, if necessary, chromatically adapted to a [=D50=] reference white.
 
 				Values greater than 1.0 are allowed and must not be clamped;
 				they represent colors brighter than diffuse white.
@@ -3868,8 +3919,8 @@ Converting predefined color spaces to Lab</h4>
 	<ol>
 		<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.
+		<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.
 		<li>Convert D50-adapted XYZ to Lab
 	</ol>
 
@@ -3882,7 +3933,7 @@ Converting Lab to predefined color spaces</h4>
 
 	<ol>
 		<li>Convert Lab to (D50-adapted) XYZ
-		<li>Convert from a D50 whitepoint (used by Lab) to the D65 whitepoint used in sRGB and most other RGB spaces,
+		<li>Convert from a [=D50=] whitepoint (used by Lab) to the [=D65=] whitepoint used in sRGB and most other RGB spaces,
 			with the Bradford transform. ''prophoto-rgb''' does not require this step.
 		<li>Convert from (D65-adapted) CIE XYZ to linear RGB
 		<li>Convert from linear-light RGB to RGB (do gamma encoding)
@@ -5392,7 +5443,7 @@ Changes</h2>
 	<li>User-defined color spaces now dashed-ident, making predefined color spaces extensible without clashes</li>
 	<li>Added lab option to the color() function</li>
 	<li>Added normative reference for CIE Lab</li>
-	<li>Clarified that prophoto-rgb uses D50 whitepoint so does not require adaptation</li>
+	<li>Clarified that prophoto-rgb uses [=D50=] whitepoint so does not require adaptation</li>
 	<li>Clarified direction of increasing angle in LCH</li>
 	<li>Clarified that color names are ASCII case insensitive</li>
 	<li>Initial value of the "color" property is now CanvasText</li>