Virtually all image editing applications offer a Hue / Saturation control (usually called 'Hue, Saturation and Lightness), and a mighty useful control it is too. If you've never got to grips with the HSL controls then check out this step-by-step guide to what they can do, and how to use them...

Step by Step

1. Although every program has a slightly different appearance the Hue / Saturation / Lightness controls themselves are very similar. There are sliders for Hue, (colour), Saturation, ('strength') and Lightness, (self-explanatory). This is the HSL dialog box from Photoshop.	2. The Saturation slider controls the 'intensity' of the colour, (to be more specific it controls the amount of grey in the colour). Increasing saturation makes colours more vivid and 'stronger'.	3. Reducing the saturation of the image moves it closer and closer to grey, with less intense, less vivid colours.
4.If you reduce the saturation all the way to zero you end up with a greyscale monochrome image. This is one of several ways digital photographers use to turn colour photos into black and white.	5. A colour's 'hue' can be defined as its position on a traditional colour wheel, and moving the hue slider rotates all the colours on the wheel by a certain number of degrees. As you move the slider you'll see every colour in the frame changes drastically, (the two colour scales at the bottom of the HSL dialog box show the 'before' and 'after' tones). It's very rare to use the hue slider on an entire image in this way.	6. Try moving the slider from left to right to see how the colours in the image are re-mapped.
7. You can create some very weird graphic effects in seconds with the Hue controls, though the results are of questionable value, photographically speaking!	8. The lightness slider isn't one you'll use that often. Increasing it moves every colour towards white...	9. ...and reducing it moves every colour towards black.
10. Let's look at some practical applications for these controls, starting with a simple increase in saturation, which can be a quick way to give a boost to the colours in scenes shot on dull or overcast days	11. Pushing the saturation up on shots taken on fairly bright days produces images with a Technicolor 'hyper real' look to them which can be very arresting.	12. Conversely, reducing the overall saturation of an image gives a subdued, low key and slightly 'timeless' look to a shot.
13. As mentioned earlier reducing the saturation of a photo produces a greyscale image; by selecting only part of the frame you can create an attractive 'selective desaturation' effect which adds interest to an otherwise rather featureless composition.	14. One of the most useful features of the HSL controls is the ability to restrict the effect of any changes to a particular group of colours. In Photoshop and Elements you can choose the colours from the 'Edit' drop down menu.	15. Here we're working only on the 'Reds' in the frame; a very quick way to change the colour of this bright red London bus without changing all the other colours in the scene.
16. And here we're reducing the saturation and lightness of the blues in the shot from step 11 to turn a glorious summer sky into one that looks ominous and grey.	17. It's not all 'special effects'; there's some practical applications too; here's a typical flash portrait half way through a tropical holiday; the combination of harsh lighting and burnt skin is far from flattering.	18. Choosing to edit the 'reds' we can reduce the saturation and move the hue slightly to the right, (which makes them more yellow), and hey presto; tanned not burnt.
19. Last but not least most HSL controls have what is known as a 'colorize' option. This allows you to remove all of the original colour from the shot and produce a toned mono image. This makes producing 'sepia' images as easy as a couple of clicks.