In this 1m 53s video, Michael demonstrates a cool technique in Photoshop to correct White Balance even if no gray card was used during the shoot. You will need to be comfortable with Curves though.
Skill level: Intermediate
Tools: Layers (50% Gray Fill, Threshold, Curves) / Blend Modes / Color Sampler Tool
Summarised for the busy person
- Create a new layer, fill it with 50% gray, set the blending mode to difference
- Create a threshold adjustment layer. Slide the slider to the left till there’s only a few areas in black which are areas closest to 50% gray
- Select the Color Sampler Tool & click at a black area to save a sampler point
- Hide the first 2 layers
- In a Curves layer, select the Gray point sampler & click on the saved sampler point in step (3) above. The White Balance is magically corrected by this action.
- Clear the saved sampler point by going back to the Color Sampler Tool and clicking CLEAR on the top bar.