title: Processing images bigger than 4096px in Core Image for iOS 8
body: <p>I am trying to write Core Image filter with custom kernel for iOS 8. My code works correct for images less than 4096x4096. For images bigger than 4096 I obtain "tile" effect. In other words it looks like image split into several sub-images and filters runs independently for each sub-image.</p>
  
  <p>Here is good sample kernel:</p>
  
  <pre><code>kernel vec4 effectFoo(__sampler source_image) {
      return sample(source_image, samplerTransform(source_image, destCoord() + vec2(200.0, 200.0)));
  };
  </code></pre>
  
  <p>I apply it to big image with size 6000x4500. I expect to get image translated by (200, 200) offset with extrapolation by border color at two sides. However, the result is "tiled", so each tile has been translated and extrapolated independently.</p>
  
  <p><img src="https://i.stack.imgur.com/x8sB2.jpg" alt="enter image description here"></p>
  
  <p>Using log in ROI callback I got evidence that Core Image split image into 4 tiles of different sizes. Biggest tile was 4096x4096.</p>
  
  <p>Thus there are two problems for me:</p>
  
  <ol>
  <li>I can't get coordinates neither in full input image nor in full output image.</li>
  <li>Core image extrapolate tiles without respect to neighbour tiles.</li>
  </ol>