Using Curves to adjust colour and white balance in pictures

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By John Sweeney - 16th of January 2007

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What is White Balance?
Any time you take a photo of a solid white object, the colour of that object will vary depending on colour temperature of the source of light that is hitting it. This can range from very blue light to very yellow/gold light. Adjusting an image's white balance refers to making corrections to the image (or adjusting settings on the camera prior to shooting) to, essentially, make the white point white. Without proper white balance, it's impossible to get proper colour in your photos.
White Point on Your Digital Camera
Most mid-range and up consumer digital cameras these days offer a variety of white point settings for different lighting conditions, natural, incandescent, fluorescent, etc. Some allow you to manually set the white point by first photographing a white object and then telling the camera to reference that as your white point.
While these methods often work well, they are not infallible and chances are, you'll need to adjust the white point yourself in post-processing on more than one occasion, particularly if you do a lot of low-light photography.

Adjusting The White Point in Photoshop
There are a few methods for adjusting and correcting white balance in Photoshop. Some will work better than others, depending on the situation and the image at hand. The method outlined below works most of the time.
Open your image in Photoshop and then bring up either the curves adjustment dialogue(Ctrl+M). sometimes curves work better than levels, but for many situations this is just a matter of personal preference. To open the Curves Pallet start on the layers pallet (F7 on your keyboard) and click on the icon at the bottom of the pallet which looks like a black and white circle and then select curves, or as listed above Ctrl M to bring up the pallet directly))When you open curves you should see the three eyedroppers at the bottom right of the pallet. (The levels dialogue also has droppers which function in a similar way).
If you run your mouse cursor over the eye droppers you will see that the droppers are labelled black, grey and white. These droppers basically operate the same way that the standard eyedropper tool does, except that they pick up the tonal value of the image rather than the colour.
So now click on the white dropper and then click on the brightest point on your image that should be white. This will adjust the image, making this setting your white point to reference that area as white.
This has made a dramatic difference, but, generally speaking, when we alter our white point, it throws off the black point, so we need to do the same technique, only this time let's use the black eye dropper and select the darkest spot on the photo.
As you will see, this is a dramatic improvement from the first image to the final result:
If you find that your colours are still off, you can use the "grey" dropper to select a middle grey value, but usually this isn't necessary. You can also fine-tune your results by going to Image - Adjust - Hue/Saturation, if you're not totally satisfied with the above procedures. The overall effect shows a vast improvement in your colour balance and an altogether pleasing look to the pictures. Go on, give it a try, you know you want to.