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POAnomalous results getting color components of some UIColors
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copied!<p>I'm trying to extract the rgb components of a <code>UIColor</code> in order to hand-build the pixels in a <code>CGBitmapContext</code>. The following sample code works fine for most of the <code>UIColor</code> constants but, confusingly, not all. To wit:</p> <pre><code>CGColorRef color = [[UIColor yellowColor] CGColor]; const float* rgba = CGColorGetComponents(color); float r = rgba[0]; float g = rgba[1]; float b = rgba[2]; float a = rgba[3]; NSLog( @"r=%f g=%f b=%f a=%f", r, g, b, a); </code></pre> <p>The results for <code>[UIColor yellowColor]</code> above are<br> r=1.000000 g=1.000000 b=0.000000 a=1.000000, as expected.</p> <p><code>[UIColor redColor]</code> gives r=1.000000 g=0.000000 b=0.000000 a=1.000000, again as expected. Similarly for <code>blueColor</code> and <code>greenColor</code>.</p> <p><em>However</em>, the results for <code>[UIColor blackColor]</code> and <code>[UIColor whiteColor]</code> seem completely anomalous, and I don't know what I'm doing wrong (if indeed I am).</p> <p>To wit, <code>[UIColor blackColor]</code> gives r=0.000000 g=1.000000 b=0.000000 a=0.000000, which is a tranparent green, </p> <p>and <code>[UIColor whiteColor]</code> gives r=1.000000 g=1.000000 b=0.000000 a=0.000000, which is a transparent yellow.</p> <p>I'd appreciate it if somebody could either:</p> <p>(1) explain what I'm doing wrong<br> (2) replicate my anomalous results and tell me it's not me, or<br> (3) hit me over the head with a big hammer so it stops hurting so much.</p> <p>Howard</p>

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