title: Wrong scaling with GPUImageTransformFilter
body: <p>I try to use GPUImage to resize a image mask to the size of an given image</p>
  
  <pre><code>-(void)imageTaken:(UIImage *)image
  {
      [super imageTaken:image];
  
  
      CGFloat sx = image.size.width / self.imageMask.size.width;
      CGFloat sy = image.size.height / self.imageMask.size.height;
  
  
      GPUImageTransformFilter *scaleFilter = [[GPUImageTransformFilter alloc] init];
      CATransform3D t3d = CATransform3DMakeScale(sx, sy, 1);
      scaleFilter.transform3D = t3d;
  
      GPUImagePicture *scaleImageSource = [[GPUImagePicture alloc] initWithImage:self.imageMask];
  
      [scaleImageSource addTarget:scaleFilter];
  
      [scaleImageSource processImage];
  
      UIImage *scaledMaskImage = [scaleFilter imageFromCurrentlyProcessedOutput] ;
  
  
      NSLog(@" sx: %f, sy : %f", sx,sy);
      NSLog(@"[image size] : %@", NSStringFromCGSize([image size]));
      NSLog(@"[_imageMask size] : %@", NSStringFromCGSize([_imageMask size]));
      NSLog(@"[scaledMaskImage size] : %@", NSStringFromCGSize([scaledMaskImage size]));
  
  
      [self.delegate photo:image
                 imageMask:scaledMaskImage takenOnPhotoMaskViewController:self];
  
  }
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>sx: 1.500000, sy : 1.126761
  [image size] : {480, 640}
  [_imageMask size] : {320, 568}
  [scaledMaskImage size] : {640, 1136}
  </code></pre>
  
  <p>By what I understand <code>[scaledMaskImage size]</code>should be <code>{480, 640}</code>, as sx is 1.5 and sy is 1.126761, but as it is <code>{640, 1136}</code>, its as scaled by 2.0. What did I do wrong?</p>