This tutorial shows how to decrease the depth of focus in an image as if the photo was made with a large aperture. The effect will isolate the subject from the background and will draw the attention of the viewer to the actual subject of the photo.

Step 1 - Copy layer

Copy to background layer twice by dragging the layer to the new layer button on the bottom of the Layers tab.

Step 2 - Extract subject

An important step is to isolate the actual subject from the rest of the picture. In Photoshop 6.0 the Extract tool was introduced, which simplifies the extraction process.

Select Image > Extract... (COMMAND/CONTROL + OPTION/ALT + X) to start the Extract tool.

Zoom in to see enough details. Use the Edge Highlighter Tool (B) to trace the outline of the subject. Use a brush size that is comfortable to work with. The Smart Highlighting option uses an automatic brush size (with a maximum of the set brush size) depending on the contrast in area of the brush; it also tries to automatically trace the outline. Remember to include both 'inside' and 'outside' in the marked line.

Use the Fill Tool (G) to fill the 'inside' area.

To check the extract process, use the preview option. The Cleanup Tool (C) can be used to remove unwanted areas. Use the OPTION/ALT-key plus the correction tool to include unselected areas.

If everything is correct, apply the Extract tool. Remember that the unselected areas are removed from this layer.

Step 3 - Prepare blurred background

Select the middle layer. Use the Clone Stamp tool to copy the area around the subject to the edge of the subject. Use a moderately small brush size and a smooth brush. This operation is necessary to prevent a halo around the subject in images with high contrast.

If this cloning was left out, the dark and light areas on the edge of the actual subject would be included in the blur filter we're about to apply. It should be a blurred version of only the background; cloning the background is the best way to simulate what's behind the actual image. By blurring it, details become invisible, so the illusion is sufficiently convincing.

Apply a Gaussian blur filter (Filter > Blur > Gaussian...); usually the Radius setting should be 4-9 (depending on the size of the photo).

The resulting layers are:

Step 4 - Mask the part that is in focus

To make part of the background around the subject to be in focus we mask part of the blurred layer. The sharp background will shine through.

Select the middle layer and create a layer mask by selecting the Add Layer Mask button on the bottom of the Layers tab.

We can now 'draw' a grey scale image that will be used as a layer mask. Dark areas will appear as transparant, white areas will appear as opaque.

In this case we use the Gradient tool to make a nice mask. Select the Reflected gradient and use the Reverse option (or swap foreground and background colours (X)). Start at the bottom of the camel and draw a little upwards. A band of the blurred layer will be made invisible.

Step 5 - the final touch

The resulting image looks convincing. Often the cut out subject has sharp edges which do not look photorealistic in print and at 100% zoom. Select the top layer and use the Blur tool to make the edges a bit smoother.

If there are objects in front of the subject these objects can be extracted to another layer. Put this layer on top of the subject layer and use the Blur filter to make it look out of focus.

With several background layers at different distances and each with a different amount of blur (Radius setting) the suggestion of depth can even be made perfect. The whole process gets increasingly complex and more time consuming.