Photo Retouching Tutorial:

Adding bokeh shallow depth-of-field to photos using Gaussian Blur filter.

Shallow Depth-of-Field Bokeh with Photoshop Gaussian Blur

Photo Retouching Tutorials

Bokeh and Depth-of-Field (DoF)

This photo-retouching tutorial will help in creating the blurring effect in found in professional photographs, typically caused by the shallow depth-of-field (DoF) that is inherent in a telephoto lens (85mm and larger). This blurring, or out-of-focus effect of the background or foreground in a photo is know as "bokeh" (pronounced "bo–kay" or "bouquet," also referred to as "creamy bokeh"), which is a combination of focal-length aberrations (aka "spherical aberrations"), and/or lens artifacts that are created when a subject is not in focus. The closer you are to the in-focus foreground subject in relation to the background, the shallower the DOF.

Bokeh (shallow DoF) creates a sense of depth, putting the "viewer" POV (point-of-view) closer to the subject. The longer the focal length of the lens, the "closer" the viewer appears to be, even though it is only an illusion. In addition, the wider the aperture setting (shot "wide open"), the greater the Bokeh effect. When the depth-of-field of the camera lens is set to infinity, or the aperture is closed down, both the foreground and background will be in focus.

In the samples below, Fig.1 was shot with a 300mm lens set to f/4 (no blurring filter used), Fig.2 was shot with a 50mm lens set to f/8 (cropped by 50%), and the background was blurred using only the Gaussian Blur filter (Radius: 14.5 pixels).

Bokeh vs Blurring with Photoshop Filters

As you can plainly see from these samples, bokeh that is caused by shallow DOF in a telephoto lens has some attributes which cannot be duplicated using only one Photoshop filter. One of these critical components is the "circle of confusion" (CoC) effect which is an optical spot caused by a cone of light rays failing to come to a perfect focus when imaging a point source of light. Although the point source will be blurred using the Gaussian filter it will not have the characteristic spherical aberrations seen through a camera lens.

Creating Bokeh with Photoshop Gaussian Blur Filter

Simple blurring alone cannot create a realistic "bokeh" effect, due to the lack of noise, and lens aberrations or artifacts, but with a combination of blurring, selective filter application, and the introduction of noise on several different layers, you can simulate this depth-of-field bokeh effect. See "before and after" samples below.

The first step is to isolate the background from the foreground using the Selection Tool. Feather the selection by 1 pixel to soften the transition. Cut and paste the background selection into a new layer titled "close blurred background" or any similar name. Then paste into a second layer titled "distant blurred background."

Select the first background layer ("close blurred background") using the Command key to isolate the pixels from the transparent area. This will prevent the blurring from bleeding beyond the selected area. Apply the Gaussian Blur filter with a Radius of around 10 pixels (below, left). You will want to experiment with this setting. Then select the second background layer ("far blurred background") and apply the Gaussian Blur filter with a much larger Radius, say around 20 pixels (below, right). This will simulate an increase in blurring as the distance increases.

Using the Eraser tool you will gradually erase the "far blurred background" layer over the closer objects in your background. Use a large feathered brush with a low Opacity setting of around 20%. As you erase away this layer the closer objects will slowly come into focus.

Adding Spherical Aberrations, Heat Distortion & Camera Noise

Using the "Pixelate>Crystallize..." filter (set Cell Size to around 30 pixels) you can add a mosaic pattern (below) that is similar to optical and lens aberrations that are typically caused by heat distortion (heat waves rising from the ground). By dialing back the opacity of this layer you can create a subtle effect to the mosaic pattern, making it blend in with the undisturbed layer.

Un-retouched photo showing heat distortion waves in a background with bokeh

If you are adventurous you can create your own 'bokeh' custom brush presets by using the Layer>Layer Style>Blending Options to create a new Brush Preset. Using a sampled lighter color (or pure white) you can zap certain areas with your custom brush - typically hotspots and/or highlights in the image background - adding those critical spherical aberrations to highly reflective objects (below, left). I will be adding a tutorial on the creation of these brush presets at a latter date.

Adding Bokeh with Pixelate and Crystallize Filters

If you don't feel like spending the time creating your own brushes there are several brush presets available online. A really nice tool to finish with is the "Bokeh Photoshop Brushes" (.abr extension) add-on custom brush presets from www.obsidiandawn.com." Using these custom brushes will add the necessary spherical aberrations which will give your newly-blurred background the necessary realism.

Load these brushes into the Photoshop Brushes palette then select some of the lighter background colors using the Eyedropper. Add this effect to a new layer that is set to "Screen." You can adjust the opacity to control the effect. You can also adjust the diameter of the spheres by using the "Master Diameter" slider setting in the Brush pull-down window. The final sample (above, right) shows the Bokeh Brush effect merged together with the Crystallize effect.

Adding Noise Back to the Photo

The final step is to merge all of your adjustment layers into one final layer and add enough noise back into the image so that it matches the camera noise in the original file. Apply the filter to a duplicate of the merged layer so that you can de-emphasize it using the opacity setting. Set the Add Noise filter's Distribution setting to "Gaussian" and check the Monochromatic box (below, left). You can play with the "Amount" percentage slide-bar so that the noise size matches your original camera noise.

Once you have the noise level as close to the original as possible you will need to blur the noise (above, right) so that it matches the softness of the camera noise in the original file. You will want to zoom in to around 300% to evaluate the noise and noise blurring effects. If the layers closely match at 300% they will look nearly perfect at 100% or smaller.

Conclusion

Obviously, using the correct lens and aperture setting would be preferable to using filters to create shallow depth-of-field and bokeh, but there are times when you may have a photo with great composition that was unfortunately shot with the wrong lens, a high f-stop setting or an inexpensive point-and-shoot camera with the focus set to infinity. In these cases, using Photoshop filters can closely approximate these natural optical effects.

Note: The following hardware and software was used in this tutorial: An Apple Mac Pro desktop computer, a Wacom Intuos 6x8 drawing tablet, Adobe Photoshop CS-CS5 photo editing software and a properly calibrated monitor.

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