add a blue sky

using: photoshop

So often dull skies ruin what could have been a great image. Yet adding blue sky to a photograph is relatively simple.

First of all there are two different types of blue sky; there's the actual sky image, which may contain clouds or other features. And there's the gradient fill of blues to give the 'middle of the desert' overhead vault that we often see on a perfect day. In reality which of these you choose is neither here nor there. What matters is getting the job done realistically and quickly.

Without the need to take screenshots, performing the task in this tutorial takes around 4-6 minutes.

NOTE: there is a PDF download of this tutorial,with his-res images, available for members.

This is the image we wish to enhance with a brand new sky. If we take a closer look we can see that the white sky shows through the leaves in places, which can be a nuisance for this kind of operation.

If we look at the individual RGB channels, we can see that the trees are in greatest contrast to the sky in the BLUE channel.

COPY the BLUE channel.

Then, on the BLUE COPY open the LEVELS and increase the contrast further by dragging the ends of the sliders towards the middle. You will have to experiment to get the right result. What you are after is black trees on a white background. Ignore the foreground for the moment.

With a large black brush, paint out the foreground so that it matches the trees, Take care not to colour in any of the gaps in the leaves where the sky shows through.

Notice that the distant mountains are still a little grey. In order to include them in the selection they will also need to be painted black.

This is the result we want; the sky has been isolated as white with everything else rendered black.

Now, with all channels turned on, go to SELECT/LOAD SELECTION... and load the BLUE COPY channel as a selection.

You will have to INVERT the selection, because what is selected currently is the sky, and we don';t want that, we want everything else.

With the trees and the foreground selected, COPY and PASTE so they become a new layer. With the BACKGROUND LAYER turned off, it will look like the image above.

What we need now is a suitable sky. Open your 'donor' sky and drag the layer BEHIND your tree layer.

As we can see, however, the meeting of the leaves with the sky is a little stark and unrealistic. In this latest version of Photoshop (CS3) there is a new tool called REFINE EDGE which does exactly what it says. CTRL/CMMD-CLICK the tree layer icon in the LAYERS panel to select the tree llayer, then turn on REFINE EDGE. This adjusts the edge of the selection, and if you do it with a black background - as shown - you can preview what will happen to your leaves against the sky.

This is only the selection you are adjusting, so once you're happy, INVERT the selection and press DELETE. The result should look like the preview in the REFINE EDGE tool.

NOTE: in PS versions prior to CS3 you can still CONTRACT the selection and FEATHER is slightly. REFINE EDGE just does this but with more finesse and settings.

The result is looking good. Next we have the distant mountains to deal with. Select the mountains (MAGIC WAND should do the trick) and COPY/PASTE into a new layer. A couple of duplicate layers set to MULTIPLY will give them the substance that was missing under the white sky.

And there's our new sky.

Cloud Free Alternative

An alternative to using a sky is to use a GRADIENT FILL sampled from a genuine sky.

The final touch involves taking the trees that used to be beneath a dull sky and giving them the saturation that would be more likely under a blue, sunny sky. The EXPOSURE coimmand in the latest version of Photoshop is brilliant for this, but there are other tecjniques, including a combination of good old-fashioned CURVES and HUE/SATURATION.

There you have it.

The image used in this tutorial is available for Members to download.

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