title: GPUImage: blending two images
body: <p>I was using GPUImage framework (some old version) to blend two images (adding border overlay to a certain image).
  After I have updated to latest framework version, after applying such a blend, I get an empty black image.</p>
  
  <p>I'm using next method:</p>
  
  <pre><code>- (void)addBorder {
      if (currentBorder != kBorderInitialValue) {
          GPUImageAlphaBlendFilter *blendFilter = [[GPUImageAlphaBlendFilter alloc] init];
          GPUImagePicture *imageToProcess = [[GPUImagePicture alloc] initWithImage:self.imageToWorkWithView.image];
          GPUImagePicture *border = [[GPUImagePicture alloc] initWithImage:self.imageBorder];
  
          blendFilter.mix = 1.0f;
          [imageToProcess addTarget:blendFilter];
          [border addTarget:blendFilter];
  
          [imageToProcess processImage];
          self.imageToWorkWithView.image = [blendFilter imageFromCurrentlyProcessedOutput];
  
          [blendFilter release];
          [imageToProcess release];
          [border release];
      }
  }
  </code></pre>
  
  <p>What is the problem?</p>