Changing Colour

Ever stop to think about how many different ways there are to change the colour of an image in Photoshop. Sometimes two different paths lead to the same result, other times one tool is clearly superior to others.

Here's a list of ways and some particular uses to which they can be put.

Image/Auto Colour - does an auto colour balance and auto contrast adjustment to the image. I most often use it as a quick preview of what an image would look like without a strong colour cast it has now. I never end up using the adjustment it makes, but I could see doing so if I had hundreds of images to present to a client - especially as proofs.

Colour Profle - not really a way to adjust colour - even though assigning a profle does sometimes radically alter the colour - its simply that without a profile the computer has no reference point. For example, some stitching programmes (PTMac) forget the profile when doing the stitching and when you reassign it in Photoshop the colour warms up considerably. Likewise Akvis Enhancer in it's preview does not take into consideration the colour profile and shows the colours as quite different. Fortunately it has no effect on the actual image that is enhanced.

Levels and Curves - increasing contrast in an image also increases colour saturation unless you deliberately set the layer effect to luminosity instead of normal (top left in the layers palette). Both levels and curves allow you to adjust each colour independently and so potentially can be used to adjust colour. Frankly I never do this as I find it way to difficult to adequately control. It's too powerful to use often though it does allow you to control colours in highlights separately from shadows (but so does colour balance tool).

A really powerful tool though is to use the grey balance tool of the curves adjustment layer to click on part of the image that should be but isn't neutral. Sometimes the result is way over the top but I can then use the layer opacity slider to tune down the colour adjustment just made. This is often better than trying to click on a different 'wanabe white' till I find the right amount of shift.

Colour Balance - this is nice to affect overall colour, or to match colour between two image layers (say in stitching (most stitching programmes do some colour balancing between image segments for you but sometimes you have to fine tune). WHile in theory you can colour balance the highlights separately from the midtones and shadows, the overlap in the control is such that really the entire image is affected regardless of which you select.

The nice thing about colour balance is that it can be used easily for subtle colour changes and it's easy to get back to the baseline by resetting to zero. Normally I use colour temperature in Camera Raw to affect the warmth of the image but if I can fine tune this with colour balance.

Hue/Saturation - is a powerful tool because you can adjust each individual colour. You can even define which part of the spectrum is covered by each individual colour slider by adjusting the range sliders on the bottom. Since it makes a difference in which order colour layer adjustments are made (which layer comes first), I usually will do an overall saturation adjustment in one layer, individual colour adjustment with a second layer. Whether it goes on top or underneeth the general adjustment depends on the effect I want. I'm afraid that if I drive saturation up to max. with one layer, tuning it down in the layer above will not restore the selected colour. It's rather like dodging till you get pure white - no matter how much you burn, you ain't gona get your image back.

Colour Channels - lets you modify the colour of individual colours. With this you can make an orange flower green or red or blue - which while cute, hopefully you don't do too often. Where I find it handier is where I want to make some more subtle changes to a colour. Let's say I'm photographing a rock and either I remember the streaks in the rock being red, or I want them red and the camera recorded them as orange. In theory I could use a masked colour balance adjustment to affect selected areas, but it's less work to take the oranges and downgrade their yellow content and increase their magenta content and voila I have red instead of orange. I did this with Sundance Rose in which the camera recorded some of the streaks in the background rock as orange instead of red. To be honest, I can't even remember whether that was accurate or not, all I know is it clashes with the red/magenta colour of the rose hips and so I modified it with the colour channels control. I commonly combine this with a hue saturation layer to really control the kind and amount of colour in a particular part of an image. I can get further control if I use masking.

Colour Filters - I confess I rarely use these but for example if you wanted just a little warming of the image without distorting the overall relationship of the colours, using a warming filter can be more subtle than adjusting colour balance.

I'm quite sure I have left out many ways of adjusting colour (eg. working on the red, green and blue image channels (which has nothing to do with the colour channel adjustment layer control) but in fact lists the controls for colour that I use.