title: Higlight Artifacts When Using Hard Light Blend Mode
body: <p>I'm blending two images in my iPhone app, using the HardLight blend mode of the top image. It looks something like this:</p>
  
  <pre><code>UIGraphicsBeginImageContext(size);
  [sourceImage drawInRect:rectangle blendMode:kCGBlendModeNormal alpha:1.0];
  [effectOverlay drawInRect:rectangle blendMode:kCGBlendModeHardLight alpha:0.75];
  mainImage.image =  UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  </code></pre>
  
  <p>It works fine. However, the blown-out highlights in the image appear with a weird color artifact. Note the purple artifact in the bottom-right corner of this photo:</p>
  
  <p><a href="http://dl.dropbox.com/u/626891/artifact.jpg" rel="nofollow noreferrer">http://dl.dropbox.com/u/626891/artifact.jpg http://dl.dropbox.com/u/626891/artifact.jpg</a></p>
  
  <p>This only occurs using Hard Light; other blend modes are fine. Anyone know what to do about this?</p>