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Adjusting Colour and Brightness

This is an art rather than a science. Not least in deciding whether or not it's necessary!

Original image (scaled)

Here's a picture of some impala taken in Zambia (July 2001; Canon AE1 SLR camera, 210mm lens, scanned from a print). It was early morning, and the light is very washed out, and I'm not the world's best photographer. There's also a distinct yellow-green colour cast. All can be corrected, but of course you may prefer the original, which does have a certain atmosphere.

• Load your image (use the above JPEG if you like). The first thing to do when enhancing a picture is look at the image's histogram, Open the Image processing window and click on Equalise (make sure Linear equalisation is selected). Open the Details pane and you'll see a graph which shows how often each colour occurs in an image. Here it shows that all the colours are in a hump in the middle, with no dark or light shades at all.
• Click on Preview, and then the Auto icon (the black and white circle). The colours (actually the brightness values, as we're looking at the RGB channel) will be stretched to fill the available range, and the contrast of the image will change markedly. This is a bit strong, so we'll reduce it in strength when we apply the effect.
• Apply using the Magic wand:Whole image tool with the Opacity slider set to 50% to soften the effect. As you've got the preview enabled, remember you'll have to click twice to apply the effect. Fix.
• Now we adjust the colour balance. In general, try to get the overall brightness and contrast right before changing the colours in an image. Go to Image processing:Balance and pull down the Details pane. Click on Preview.
• You can start tweaking the sliders to adjust the colour, but this is very difficult to get right unless you know exactly what you want to do. A much better method is to use the Sample neutral point facility.
• Look at your picture, and try to spot an area you know should be grey. I chose the bark of the tree in the centre of the picture.
• Click on the Sample neutral point syringe.
• Hold down the Alt key, and drag out a rectangle over the area you've chosen, as shown below. If you're practising with the image from this web page you may find it helpful to zoom in. Try to select an area as single-hued as possible; avoid including any leaves and suchlike.

  

  Remember to hold down the Alt key

• Some numbers will appear in the Details window and the sliders will move slightly. And since Preview is on your picture should update to look something like the picture below (but paler). If it doesn't look right try getting another sample.
• When you're happy, apply with Magic wand:Whole image (remember to change the Opacity to 100%). Fix.

Here's the result. As a further adjustment, I boosted the contrast slightly (Image processing:Gamma:Increase contrast). If you like, try some slight sharpening.

Stretched, colour-balanced, contrast-enhanced and sharpened