The ability to isolate a single colour in your photographs is one of the best examples of how digital photography can offer techniques and effects that are difficult to create with film. While the effect is certainly possible in a chemical darkroom, it's a time-consuming process. Follow this tutorial and you'll be able to knock up a finished example on your PC in less than 10 minutes.

The best reason to create an image with a strong isolated colour – or a bold area of isolated colours – is to add impact to an element that otherwise gets lost in the composition. It can add poignant impact to a small but crucial detail, and can be a way of tugging on people's heartstrings.

Examples in photography abound – visit any tourist art market and you're bound to see a few. London telephone boxes and double-decker buses are typical examples. The fact that the technique is so popular tells you all you need to know – it gets the message across, and can turn a dull photograph onto one with an instantly obvious focal point.

Choosing your shot

The popularity of colour isolation means you need to be careful using it. You're unlikely, for instance, to find many coffee table books stuffed with colour-isolated images. As with any technique designed to have an emotional impact, overdoing it will result in images that are exhausting and repetitive to browse through.

Your best bet is to pick one photo on which the effect works well and use that, rather than applying the technique to everything you shoot.

Isolate colours in photos

While isolating a colour can save a dull photo, it's good practice to use shots that you're already happy with. Tight zooms don't work well, but choose an image with a strong, clear and brightlycoloured main subject. Bold red generally works well, hence the popularity of buses and telephone boxes.

Composition isn't so important when choosing a shot – you're forcing the viewer to notice what you want them to by rendering an object in colour, so this is a good way to use an image that's sharp and well exposed, but slightly off compositionally.

What you'll need

As well as your image, you'll need something to edit it with. The techniques used here can be translated easily to GIMP (available to download free from www.gimp.org), but most users will have more success with Photoshop Elements (£78 from www.adobe.co.uk). Elements is not only a more comprehensive application, offering a capable library as well as an editor, but some of its tools - such as quick selection - are more refined and quicker to use.

Applications that don't allow proper 'per-pixel' editing, such as Adobe's Lightroom or the free Picasa, aren't good for this kind of work. You might find that your camera has an automatic colour isolation setting, removing the need to edit your images in post-production at all and leaving you with roughly the same effect.

Isolate colours in photos

Getting going

Before you begin the walkthrough, make sure your image is otherwise finished. That means that any sharpening, cropping or tone curve adjustments should be completed before you start. Attempting to finish a photo that's already had major work done on it will result in loss of detail, particularly if you're working on a JPG image rather than a Photoshop PSD file.

When editing your image initially, remember that you're aiming for an over-the-top effect. Feel free to overdo the saturation, paying particular attention to the area that you intend to remain in colour – we're going to make sure there's plenty of contrast in the background on the final image, so make sure the colour stands out.

With this technique, representing reality accurately is secondary to achieving maximum impact. It's also a good idea to work on a copy of your image in case you save an imperfect version accidentally. Open your prepared image and save it as a work in progress file. If you're using Photoshop, saving the image as a PSD file is generally a good idea.

PSD files have a few strengths for this kind of work – crucially, they don't degrade in quality each time you save them, as JPGs images do. They also support layers, which means that once your image is finished, you don't need to flatten it and lose the ability to make wholesale changes later.

The only time you should save your work as a JPG is when it's totally finished and ready for print or uploading to an online photo album.

How it works

This technique works because of the support many advanced editing applications have for layers. A layer is a simple concept – it's effectively another image that fits exactly on top of your first image, all within the original file.

Each layer can have elements added to it such as text, and in Photoshop it can work as an adjustment layer, filtering the image beneath to give it more saturation, for example, without editing the original pixels.

In this example, we use layers very simply. The topmost layer of the image is a black and white version of the original photograph, with areas carefully removed to reveal the colour version beneath. If you have a steady hand (particularly in conjunction with a graphics tablet), you may find that you're able to simply erase sections of the topmost layer on some images by hand. In most cases, however, it will make sense to select an area precisely first and use your selection as a guide.

Isolating colours with Photoshop Elements

1. Prepare layers:

Open your image (ideally from a copied file so you have a backup), and pay attention to the Layers palette. If you can't see it, click 'Window | Layers'. You'll see a thumbnail – right-click it, choose 'Duplicate layer', and click 'OK'.

Nothing will happen to your image, but you now have two layers – one on top of the other. Making one layer black and white and exposing parts of the layer below will produce our effect.

1. prepare layers

2. Convert to mono:

Go to 'Enhance' on the menu bar and click 'Convert to black and white', or use [Ctrl]+[Alt]+[B] on your keyboard. A few styles are listed for you to click through, with the results previewed both in the conversion window and in the main image window.

Our advice is to go for something with a medium amount of contrast – not too bright or too dark. Click 'OK' when you're happy with your choice.

2. convert to mono

3. Zoom in:

This technique works by selecting an object in your photo, then removing it from the topmost layer, allowing the coloured layer to show through. It's always best to work very carefully – mistakes might not be obvious when reviewing your images on screen, but they will be once printed.

Click the magnifying glass in the toolbar or press [Z] , then click and drag around the object you want to select to zoom in on it.

3. zoom in

4. Select object:

Click the Quick Selection tool or press [A]. This tool works by selecting adjacent areas of your image which are the same colour or texture. Click and drag the mouse pointer over the part of your image you want to colourise, and don't worry if the selector makes the odd mistake. The edges will be refined when you let go of the mouse button, and the next step demonstrates how to refine your selection.

4. select object

5. Fine-tune selection:

It's very important that you don't tolerate a less-than-perfect selection, because it will have a negative impact on your final image. If the selection tool has chosen inappropriate parts of your image, press [Alt] and click and drag the mouse pointer over them. This will remove them from your selection.

Similarly, if you remove part of your selection that you wanted to keep, simply click and drag back over it.

5. fine-tune selection

6. Delete selection:

Tap [Delete], and the area you've selected will be removed, allowing the layer beneath, which is still in colour, to show through. Zoom to 100 per cent and make sure the edges look bold and confident If you find an area that needs editing, the Eraser tool (press [E]) is a good way of carefully removing stray black and white elements.

Once you're happy, save the file with layers as a PSD document.

6. delete selection

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Liked this? Then check out How to create Photoshop panoramas in Elements 9

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