Photoshop offers many excellent methods for correcting casts. But if you can’t work out what they are, how can you fix them?
The first and most important step is to familiarise yourself with the color Wheel:
It’s important to know instinctively what colors are adjacent to each other, and what colors are opposite to each other.
Study that color wheel, learn it, make one of your own and pin it up on your wall if you have to. It’s a great tool.
Read the cast:
When you look at a photo, or part of a photo, and say “There’s something wrong with the color”, then you need to be able to do two things:
(1) identify the problem color; and
(2) identify the adjacent or opposing color that will fix it.
Some casts are easy to identify, others are harder. To make it simpler, let’s discuss the two types of cast – cast in neutrals, and cast in colors.
Cast in Neutrals
Cast in neutrals is generally global cast, and that’s addressed by white balance. If you shoot Raw, you should be fixing white balance in your Raw converter, and the problem should rarely reach Photoshop at all.
If you can see something in your photo that should be white or gray, but isn’t, then you’ve got yourself a neutral cast. Cast in neutrals is fixed by subtracting the problem color, adding the opposite color, or occasionally by desaturating.
Global casts, and even localised casts in neutrals, can almost always be summarised as either “too warm” or “too cool”. That’s a pretty broad generalisation, but it should help you a great deal. Use a Photo Filter adjustment layer and try the Warming filters (if your photo is too cool) or the Cooling filters (if too warm).
It’s pretty easy to spot casts in neutrals, because our feeble eyes and brains have a pretty good idea of what gray is supposed to look like, thanks to Adobe assisting us with all the other gray on the screen (palettes etc).
Cast in colors
Identifying casts in colors is tougher, particularly because they usually only occur in small areas here and there. If you’re having trouble, here’s a couple of things to keep in mind …
(a) The six colors in the color Wheel tend to fall into three “cast groups” – Red/Magenta, Blue/Cyan, and Yellow/Green. How is this helpful? Well, if you think a cast is yellow, for example, but fixing yellow isn’t working, the real cast is probably the other color in the “cast group” – ie green. Likewise, when you think there’s a red cast, it’s often actually magenta, and when you think there’s a blue cast, it might be cyan instead.
(b) A cast will always be one of the colors beside the desired color. Take a look at the color Wheel again. If you are trying to fix a cast in a yellow shirt, for example, the cast will be either red or green, because they are the colors either side of yellow on the wheel. In skintones, which are red, the cast will always be either magenta or yellow.
(c) A color can’t have its own cast. Well, that sounds like commonsense, doesn’t it? Can a blue sky have a blue cast? Of course not. Can green grass have a green cast? Of course not. But for some reason many people complain “my skintones have a red cast”. That’s impossible, because skintones are red. See the previous point.
(d) Dull color is a form of cast, but often its correction is as simple as adding some saturation. Don’t try to over-engineer it – if the colors are correct, just a bit lifeless, then boost them up!
Practise Practise Practise
Like everything about digital imaging, don’t expect to learn this overnight – it takes patience and practice.