There is a quick and easy way to use Photoshop to correct for a color cast in a photo. It is described in today’s email issue of Digital Darkroom Questions (DDQ) and is reproduced (with permission) below.
The contents of the email that follows (between the asterisks ***) are copyrighted by Tim Grey.
When I was at Photoshop World in Orlando I saw you present a cool technique for fixing really bad color casts in an image, but I missed part of it. Can you remind me of the steps involved?
Absolutely. This techniques comes across as being pure magic (which is why I like to present it!), and it can be incredibly helpful when you have an extreme color cast. This can happen with digital captures when the color temperature is set to a wrong value, but usually this degree of color cast comes from things such as old color photos that have become faded or otherwise shifted in color with time.
The first step is to create a copy of the Background image layer by dragging that layer to the Create a New Layer button at the bottom of the Layers palette. Then you need to determine the color of the color cast so you can compensate for it. To do so, select Filter > Blur > Average from the menu. This will convert this layer to a single color that represents the average color of all pixels in the image. Of course, this is the problem color, so you need to determine the opposite of it so you can apply it as a compensation for the color cast. To determine that opposite color, select Image > Adjustments > Invert from the menu. This will convert the layer to the opposite of the average layer, which means it is the opposite of the color cast.
To apply this color to the underlying image, set the blend mode to Color using the dropdown at the top-left of the Layers palette. This blend mode will cause the layer to alter only the color of the underlying image, completely offsetting the strong color cast. The problem is, this will result in too strong an effect, with a color cast that is the opposite of the original, but much stronger. To tone things down and produce an image without a color cast, simply reduce the Opacity using the slider at the top-right of the Layers palette. Adjust the value until you have a perfectly neutral color in the image.
The final result will represent relatively accurate color, but it will probably appear a bit flat and possibly lacking saturation. To compensate for this you’ll need to boost saturation (using a Hue/Saturation adjustment layer) and contrast (using Levels or Curves).
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