Selective colouring of a part of an image can be very effective and appears to be quite popular among digital enthusiasts. It usually involves making a selection within your image, but what do you do if your image is a complicated one and a selection is not easy to make?

Why not use Photoshop's layers and layer masks and dispense with the selection completely. The advantage is that you can undo mistakes at any stage and repair them and it is easy to work at high magnification for the best result. We chose to separate the tree trunk from our leaves to make the leaves stand out far better than in the original image shown below.

Call up the layer's palette by pressing the F7 key and make a duplicate of your layer by dragging the thumbnail down over the copy icon at the base of the layer's palette.

You can rename your layers if you wish and we chose leaves for the bottom layer and Tree trunk for the upper layer. It is a good idea to get into the habit of giving your layers a label. While not essential with two layers, with 10 layers it can be essential. Click inside the bottom layer and it will turn blue to indicate to you that it is active. Turn off the top layer by clicking on the little eye as shown in the image below.

By using two layers you can adjust the levels and/or the colour saturation of the leaves and ignore the effect on the tree trunk. Just concentrate on getting the leaves correct to your liking. Then select your tree trunk and make what adjustments you want to the bark ignoring the effect on the leaves.

Try selecting Image-Adjust-desaturate to remove all colour from the tree trunk. Whenever you convert a colour image to monochrome you will probably find that you need to increase the contrast. Select Adjust-Brightness/Contrast from the image menu and move the sliders to get a satisfying result.

You now have your two layers separately adjusted. In the bottom "Leaves" layer you have the saturation and levels correct and in the upper "Tree trunk" layer you have a monochrome image with good sparkling contrast.

You now need to add a layer mask to amalgamate the best parts of each layer. Select your top layer and click the icon at the bottom left of the layer's palette. A layer mask will appear as a white square to the right of your thumbnail as shown below.

Generally your layer mask cannot be seen on screen, but you can view it by holding the Alt key and clicking on the mask. Click on the little eye to return your image.

Select your air brush tool and a soft edged brush and enlarge your image to somewhere around 400%. Apply the airbrush to just the leaves and you will see that it masks the monochrome top layer allowing the colour layer from below to show through. A little practice is all that is needed before you get the hang of it. Choose a magnification and brush size that makes the masking process as easy as possible and gradually reveal those coloured leaves from the bottom layer.

If you make a mistake select white as your foreground colour and repair the damage. Once you have finished the process, hold the Alt key again and click in the layer mask thumbnail. You will see that the mask looks somewhat different now and you can adjust your mask while in this mode if you wish.

You may decide that leaving your tree black & white with the green leaves contrasting against it is sufficient. However, try adjusting the hue and saturation of the top layer by calling up the palette from the Image-Adjust menu. Tick the colourize box and adjust the hue and saturation sliders to add a nice sepia tone, which will separate the leaves even more.

It doesn't take too much imagination to see how this technique could be used elsewhere. You could use the same technique to put a background out of focus in a portrait for instance or add a zoomed blur to give a subject the effect of movement or speed.