Photo Editing
Colour Balance

Getting the colour right can be the most difficult part of photo editing but a little knowledge of how the colours are made will make this much easier. On the right we have a 'colour wheel' to help illustrate the concepts that you need to grasp.

All colours are made from three primary colours - red, blue and green. Forget what you learned in Art at school we are now dealing with light not pigments.

Where the three colours overlap in the middle of the colour wheel we get a neutral grey (somewhere between black and white depending on the intensity of the colours). I have faked it here slightly for the purpose of illustration.

Where two of the colours overlap they form other colours known as 'subtractive primary colours'. Another way of looking at it is that if you remove one colour from the middle of the wheel you will get a new colour. For example, if you remove red from grey you will be left with a mixture of blue and green, this colour is called 'cyan'. If you remove or subtract green from neutral grey you are left with a mixture of red and blue known as 'magenta'. Red and green combine to make the third 'subtractive primary colour' - yellow. Knowlege of these six colours and how they relate to each other will enable you to correct any colour cast in a picture.

Now let's look at the tools available in Photoshop to help you with colour correction. First and most primitive there is auto colour (auto levels is a combination of auto colour and auto contrast). Auto colour can be found on the 'image->adjustments' menu. It works on a well established principle that has been used in the photo finishing industry for many years. Observation of the photographs that the 'man in the street' takes led to the conclusion that in 95% of all photos taken the colours in the picture, when integrated or added together, balance each other out and integrate to neutral grey.

The large machines that were used to print your photos from negatives all worked on the same principle, they put a diffuser in front of your negative and adjusted the colour head to print grey. As I said this worked well enough in 95% of all photos sent to the labs and it can indeed work well in Photoshop. If your composition 'fits the mould', and an awful lot of them do, then 'auto colour' will work very well.

If, on the other hand, you have a predominance of one side of the colour spectrum in your picture then 'auto colour' will introduce a colour cast of the opposite colour. When this happens, and the photo looks worse than it did before, hit the 'undo' button and move on to the next tool.

Colour Balance

Selecting the 'colour balance' choice on the 'image->adjustments' menu brings up the window below.

This is by far the best window for adjusting the colour of photographs. Unlike some of the other windows for adjusting colour, like the 'hue saturation' window, this one is quite subtle in it's effect and, unlike the 'variations' window, you can preview the effect on the actual picture itself.

First let's talk about the 'tone balance' box at the bottom. You'll find that most of the time you can leave the radio button set to 'midtones' for best results, unless you are dealing with very difficult lighting. Keep the 'preserve luminosity' ticked to stop the picture getting darker or lighter as you change the colour.

Now let's move on to the 'colour balance' box. Here you can see the colour wheel in action. The three sliders show the opposing colours at each end. Look carefully at your picture, decide which colour you need to decrease and adjust the appropriate slide. The hard part is deciding which colour you need to get rid of, I have a lot of trouble deciding between cyan and green, also between green and yellow. Try different sliders to see whether the colour cast is disappearing and to see whether you are introducing a new, different colour cast. If too much of the new colour is appearing before you have got rid of the colour cast you are trying to get rid of, then you have got the wrong colour. I realise that the last sentence may be a bit hard to follow so here's an illustration.

The picture above is too red right? The opposite of red is cyan so let's dial in some cyan.	Now the picture is turning blue even though it still looks a little too red.	The first picture wasn't too red it was too magenta. We needed to add green not cyan.

You might argue that the last picture is too yellow though, as it was taken in the late afternoon sun, that is the way I think it should be. There are no 'right' and 'wrong' answers to colour balancing, in the end, it's what you like. You can drive yourself crazy trying to get the colour right, especially on an indoor picture under mixed lighting or a picture taken on a cloudy day that you would like to brighten up, it's just good to be able to 'fine tune' the colour in your photographs.

I mentioned the 'variations' window that you will find in Photoshop at the bottom of the adjustments menu. This is quite good for complete beginners and for pictures that are a long way out of balance but I find that it is quite difficult to see what the effect is going to look like from the preview window so I don't use it very often.

The 'hue & saturation' window that I also mentioned earlier is more for creating colour effects and one slider covers the whole colour spectrum. The adjustment is far too coarse for the small amounts of colour change we need.