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copied!<p>I'm not really sure I have grasped the question, so this is a real punt.</p> <p>But I noticed LaC's answer depends on the pixels being written on top of each other in the normal way. In the manner you would in Photoshop call the "Normal Blend Mode".</p> <p>You can merge two layers in lots of other ways including "Multiply":</p> <p><img src="https://i.stack.imgur.com/MweNX.jpg" alt="enter image description here"></p> <p>This individually multiplies the R, G, and B of each pixel. So if you had the text on a white background, you could get a further-back layer to show through by setting the top layer to "Multiply" which causes both layers to burn into each other like so.</p> <p>This should work for your use case too:</p> <p><img src="https://i.stack.imgur.com/ofnuG.png" alt="enter image description here"></p> <p>Both text layers in this shot have an opaque white background, but the one on the right has the blend mode set to "<strong>Multiply</strong>".</p> <p>With "Multiply":</p> <ul> <li>white pixels in the top layer multiply lower layers by 1, leaving them unchanged</li> <li>black pixels in the top layer multiply lower layers by 0, reducing them to black</li> <li>shades in between darken the lower layers proportionally</li> </ul> <p>In other words, the same result that you would have got just laying the text directly onto the background.</p> <p>I haven't subpixel antialiased the text in this screenshot but it would work equally well with differing R, G, and B values.</p> <hr> <p>I'm not remotely familiar with Mac's API, but according to <a href="http://parmanoir.com/Photoshop-like_compositing_with_Core_Animation" rel="nofollow noreferrer">this link</a>, Core Animation does have this capability, which you get by writing:</p> <pre><code>myLayer.compositingFilter = [CIFilter filterWithName:@"CIMultiplyBlendMode"]; </code></pre> <p>or</p> <pre><code>myLayer.compositingFilter = [CIFilter filterWithName:@"CIMultiplyCompositing"]; </code></pre> <p>(I have no idea what "Blend Mode" vs "Compositing" relates to in Mac parlance so you'll have to try both!)</p> <hr> <p>EDIT: I'm not sure you ever specified your text was Black. If it's White, you can use a white-on-black layer set to a Blend Mode of "Screen".</p>

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