[css-color] Fix the CMYK -> RGB naive conversion algo.

Author: tabatkins

css-color/Overview.bs

@@ -1732,19 +1732,19 @@ Converting Between CMYK and RGB-Based Colors</h3>
 	Otherwise:
 
 	<ul>
-		<li><code>red   = 1.0 - min(1.0, cyan + black)</code>
-		<li><code>green = 1.0 - min(1.0, magenta + black)</code>
-		<li><code>blue  = 1.0 - min(1.0, yellow + black)</code>
+		<li><code>red   = 1 - min(1, cyan    * (1 - black) + black)</code>
+		<li><code>green = 1 - min(1, magenta * (1 - black) + black)</code>
+		<li><code>blue  = 1 - min(1, yellow  * (1 - black) + black)</code>
 		<li>Alpha is same as for input color.
 	</ul>
 
 	To <dfn title="naively convert from RGBA to CMYK | naively converted to CMYK">naively convert from RGBA to CMYK</dfn>:
 
 	<ul>
-		<li>k = 1 - max(r, g, b)
-		<li>c = (1 - r - k) / (1 - k), or 0 if k is 1
-		<li>m = (1 - g - k) / (1 - k), or 0 if k is 1
-		<li>y = (1 - b - k) / (1 - k), or 0 if k is 1
+		<li>black   = 1 - max(red, green, blue)
+		<li>cyan    = (1 - red - black)   / (1 - black), or 0 if black is 1
+		<li>magenta = (1 - green - black) / (1 - black), or 0 if black is 1
+		<li>yellow  = (1 - blue - black)  / (1 - black), or 0 if black is 1
 		<li>alpha is the same as the input color
 		<li>fallback color must be set to the input color
 	</ul>
@@ -2990,9 +2990,10 @@ The CMYKColor Class</h3>
 
 			<pre>
 			function() {
-				const r = 1 - Math.min(1, this.c + this.k);
-				const g = 1 - Math.min(1, this.m + this.k);
-				const b = 1 - Math.min(1, this.y + this.k);
+				const k_ = 1 - this.k;
+				const r = 1 - Math.min(1, this.c * k_ + this.k);
+				const g = 1 - Math.min(1, this.m * k_ + this.k);
+				const b = 1 - Math.min(1, this.y * k_ + this.k);
 				return new RGBColor(r, g, b, this.a);
 			}
 			</pre>

css-color/Overview.html

@@ -82,7 +82,7 @@
 </p>
   <h1 class="p-name no-ref" id=title>CSS Color Module Level 4</h1>
   <h2 class="no-num no-toc no-ref heading settled heading" id=subtitle><span class=content>Editor’s Draft,
-    <span class=dt-updated><span class=value-title title=20140714>14 July 2014</span></span></span></h2>
+    <span class=dt-updated><span class=value-title title=20140715>15 July 2014</span></span></span></h2>
   <div data-fill-with=spec-metadata><dl>
 	<dt>This version:
 	<dd><a class=u-url href=http://dev.w3.org/csswg/css-color/>http://dev.w3.org/csswg/css-color/</a>
@@ -1884,19 +1884,19 @@ <h3 class="heading settled heading" data-level=9.1 id=cmyk-rgb><span class=secno
 	Otherwise:</p>
 
 	<ul>
-		<li><code>red   = 1.0 - min(1.0, cyan + black)</code>
-		<li><code>green = 1.0 - min(1.0, magenta + black)</code>
-		<li><code>blue  = 1.0 - min(1.0, yellow + black)</code>
+		<li><code>red   = 1 - min(1, cyan    * (1 - black) + black)</code>
+		<li><code>green = 1 - min(1, magenta * (1 - black) + black)</code>
+		<li><code>blue  = 1 - min(1, yellow  * (1 - black) + black)</code>
 		<li>Alpha is same as for input color.
 	</ul>
 
 <p>To <dfn data-dfn-type=dfn data-noexport="" id=naively-convert-from-rgba-to-cmyk title="naively convert from RGBA to CMYK | naively converted to CMYK">naively convert from RGBA to CMYK<a class=self-link href=#naively-convert-from-rgba-to-cmyk></a></dfn>:</p>
 
 	<ul>
-		<li>k = 1 - max(r, g, b)
-		<li>c = (1 - r - k) / (1 - k), or 0 if k is 1
-		<li>m = (1 - g - k) / (1 - k), or 0 if k is 1
-		<li>y = (1 - b - k) / (1 - k), or 0 if k is 1
+		<li>black   = 1 - max(red, green, blue)
+		<li>cyan    = (1 - red - black)   / (1 - black), or 0 if black is 1
+		<li>magenta = (1 - green - black) / (1 - black), or 0 if black is 1
+		<li>yellow  = (1 - blue - black)  / (1 - black), or 0 if black is 1
 		<li>alpha is the same as the input color
 		<li>fallback color must be set to the input color
 	</ul>
@@ -3098,9 +3098,10 @@ <h3 class="heading settled heading" data-level=15.4 id=api-CMYKColor><span class
 			Defined as follows in ECMAScript:
 
 			<pre>function() {
-  const r = 1 - Math.min(1, this.c + this.k);
-  const g = 1 - Math.min(1, this.m + this.k);
-  const b = 1 - Math.min(1, this.y + this.k);
+  const k_ = 1 - this.k;
+  const r = 1 - Math.min(1, this.c * k_ + this.k);
+  const g = 1 - Math.min(1, this.m * k_ + this.k);
+  const b = 1 - Math.min(1, this.y * k_ + this.k);
   return new RGBColor(r, g, b, this.a);
 }
 </pre>