Image Analyzer examples

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Retouching portraits

A major challenge in retouching portraits is to soften the skin and still make them appear appear natural and not too smooth and plastic-like. To achieve that we need to keep some of the texture in the skin and only smooth out selected details.
This can be done with what is called a band-stop filter in signal processing and sometimes referred to as degrunge photography papers. In digital image processing the "frequency" in an image is the inverse of the size of local features in pixels, so small features like the pores of the skin are high frequency contents and larger features like the nose are low frequency contents. Skin imperfections like wrinkles usually falls somewhere in between in the frequency domain and it is possible to make a filter that reduces only frequencies in this band.
You can see a visualization of the frequency contents in an image and play with removing some of them globally in Image Analyzer's Frequency domain filter dialog, but this is too hard to control when we want to use it for retouching portraits.
Instead we want to make "degrunge" brush that is matched to the photo we are working on and which we can apply to selected regions of it. This is fairly easy to do in Image Analyzer - see how below the example.


Model: Aisling Nee. (Click the images to open in high resolution.)

• Open the photo in Image Analyzer and create two copes of it - just select copy and then paste twice.
• Smooth the first copy just enough hide the details that we don't want to keep. In this example it can e.g. be done with a gauss filer of size 15 (Operations | Filters | Smooth).
  
  
  
  
• Smooth the second copy just enough to hide the details that we do to keep. This may seem a bit counter intuitive but don't worry, we will get them back in a minute. I have done it with a gauss filer of size 3.
  
  
  
  
• Now we need to combine them to get a band-stop filtered image. This can be done in the (Operations | Pixel Format Conversion | Combine images dialog). Just set it up like this:
  
  
  
  This will produce an image that all in all does not look very appealing but at least then skin has softened but not too smooth look we were after. I may have overdone it a bit in the sample, but you can play with other filter values to achieve even better results...
  
  
  
  
• Now we can to transfer only the skin to the original photo. This can be done with the Clone brush in the toolbar. Activate the combined result image, select the Clone brush and then first click on the image while holding the [Ctrl] key down and then click again in the same spot without holding the key. It important that the two clicks are made without moving the mouse because we want to clone to the exact same location.
• Activate the original photo and begin painting on the skin - but only on the skin and avoid painting across edges. This will clone the pixels from the filtered image. You can adjust the brush size and softness in the toolbar.