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The colour of a sky can make or break a photo. Deep blue skies, or even stormy-looking ones can elicit oohs and ahhs, whereas a large expanse of overcast whiteness above the horizon can spoil otherwise spectacular subjects. Even if there was some blue up there, it could be washed-out as a result of carefully exposing the foreground.

Fortunately, a few careful clicks and drags can give your photo the blue sky it truly deserves. Whether you are enhancing what little blue there is, or generating an entirely new sky from scratch, there is several tricks that can yield effective results.

The most obvious way to create a blue sky is to select the existing one and fill it with a nice shade of blue. This, of course, creates an unconvincing result, but a giant leap in realism can in fact be had for not much extra effort.

While the latest version of Photoshop is packed with all manner of sophisticated retouching tools, one of the most effective for creating blue skies is the Gradient tool. Simply choose the start and end colours, then drag a line from where you want the gradient to begin and end. To create a realistic blue sky using the Gradient tool, choose a nice blue for the start, and transparency for the end. Then select the overcast sky area on your photo and drag a vertical line down from the top of the picture to just below the horizon line. Photoshop will fill the selected area with a smooth blend from blue to transparent, revealing a realistic white band just above the horizon.

Other tricks covered in this masterclass include pasting copies of genuine blue skies into overcast selections, or enhancing faint wisps into something

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more solid. Oohs and ahhs are only a few clicks away.

Sky selections

We've discussed several means of generating or enhancing blue skies, but all demand accurate selections of the existing overcast area in order to look remotely convincing. Photoshop offers several tools for making selections, and depending on both the foreground and background, you will find some are more effective than others.

If your sky really is pure white and the foreground is well defined, then you should first try the Magic Wand tool. You may need to adjust the tolerance and perhaps shift-click a few areas that aren't selected by the initial sweep, but it is an effective tool for this kind of job.

Unfortunately, what may have looked like a clean selection may reveal undesirable outlines after you have created, pasted or adjusted the sky. For a number of reasons, the Magic Wand's automatic selection may not sufficiently press up against the outline of your foreground.

If this happens, step back to the point at which the selection was made, then choose Select>Modify>Expand from Photoshop's Select menu. This allows you to expand the selection by a number of pixels into the subject; the number required depends on the resolution of the image, but one or two pixels can prove effective on average digital camera photos.

If your foreground is proving too complex for the Magic Wand to cut out convincingly, then you may need to create a mask. First, double-click the image in your Layers palette and click OK to turn it into a normal layer, and then drag this down to the icon at the bottom of the palette to create a new layer. With this new copy layer active, choose Image>Adjustments>Threshold and drag the slider until the foreground is a black silhouette and the sky remains white.

You can now use the Magic Wand to select the black area, then click the Eye icon on this layer in the palette to make it invisible. You should now see your colour foreground with a selection around its edges. Finally click the icon at the bottom of the Layers palette to Add Layer Mask. This turns the sky area transparent and allows you to add a blue sky underneath, either using a gradient fill or by pasting in an existing blue-sky image.