post processing - How to set white balance when there's no neutral region to select with the eyedropper?

If, in an image, there is no region which is neutral white, grey or black, how to set white balance?

Answer

You can mimick auto white balance using Photoshop's Average Blur filter in a duplicate throw-away layer. This will determine the overall color cast in the image. Then add a curves adjustment layer, use the gray point eye dropper and click on your average blur layer, which will turn it to grey. In other words the curves layer will neutralize that color cast. Then remove the average blur layer, and the curves layer will make that same adjustment on your overall image.

This is basically what your auto white balance does in camera. Samples all the light coming in and adjusts.

If your image is a close up of skin (red) or a forest (green), then the light should have a red or green cast to it, so this technique may overdo the adjustment (so may your auto white balance). If so adjust the opacity of the curves adjustment. It will at least point you in the direction of removing the dominant color in the image.

So the steps again are:

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  duplicate your layer in Photoshop

  
  


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  in the top layer, Filter > Blur > Average

  
  


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  add a curves adjustment layer

  
  
  


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  use gray point dropper, select the color in the average blur layer

  
  


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  delete the average blur layer

  
  


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  adjust opacity of curves layer