[css-color-4] ProPhotoRGB space, #292

Author: svgeesus

css-color-4/Overview.bs

@@ -2007,6 +2007,40 @@ Predefined colorspaces: ''srgb'', ''image-p3'', and ''rec2020''.</h3>
 				<tr><th>Black luminance</th><td rowspan="2">0.5557 cd/m<sup>2</sup></td></tr>
 			</table>
 
+		<dt><dfn>prophotorgb</dfn>
+			<dd>
+				The ''prophotorgb'' colorspace accepts three numeric parameters,
+				representing the red, green, and blue channels of the color,
+				with each having a valid range of [0, 1]. The transfer curve is
+				a gamma function with a value of 1/1.8.
+				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 primaries chosen to allow
+				a wide color gamut and to minimise hue shifts under tonal manipulation.
+				It is often used in digital photography as a wide gamut
+				colorspace for the master version of
+				photographic images. The ''prophotorgb'' colorspace allows CSS to
+				specify colors that will match colors in such images
+				having the same RGB values.
+
+				The white luminance is given as a range, and
+				the viewing flare (and thus, the black luminance)
+				is 0.5% to 1.0% of this.
+
+				It has the following characteristics:
+
+				<table>
+					<thead><td></td><td>x</td><td>y</td></thead>
+					<tr><th>Red chromaticity</th><td>0.7347</td><td>0.2653</td></tr>
+					<tr><th>Green chromaticity</th><td>0.1596</td><td>0.8404</td></tr>
+					<tr><th>Blue chromaticity</th><td>0.0366</td><td>0.0001</td></tr>
+					<tr><th>White chromaticity</th><td>0.3457</td><td>0.3585</td></tr>
+					<tr><th>Transfer function</th><td rowspan="2">1/1.800 </td></tr>
+					<tr><th>White luminance</th><td rowspan="2">160.0 to 640.0 cd/m<sup>2</sup></td></tr>
+					<tr><th>Black luminance</th><td rowspan="2">See text</td></tr>
+				</table>
+
 		<dt><dfn>rec2020</dfn>
 		<dd>
 			The ''rec2020'' [[!Rec.2020]] colorspace accepts three numeric parameters,