Background blur II. in Photoshop

This article introduces an excellent Photoshop filter called Lens Blur. Although there are already more blurring tools than one would possibly need, there was a definite demand for Lens Blur, since, instead of vanilla blur, it emulates the blurring effect of lenses. Therefore, it shall be perfect for the procedure below which tries to imitate the unique effect of Tilt objectives.

Load the photo

The type of blur we want to produce requires a photo which shows objects/buildings/people from a remote, elevated point of view. A photo of the city taken from a nearby hill should be perfect.

Now you have to choose which part of the picture should remain sharp. We chose the slightly askew road through the bridge.

Putting the mask on

Click the lower Edit in Quick Mask Mode icon on the Tools palette (or press Q). Quick Mask mode lets you prepare a mask with Photoshop’s  painting tools. Masks help preserving selected areas. Subsequent changes affect only the areas outside the mask.

In order to preserve the road on the bridge, activate the Gradient tool (press G), and select the Reflected Gradient option at the top. This produces a bi-directional blur transition.

Click the middle of the road and drag an orthogonal straight line towards the top of the picture. This produces a mask that becomes gradually transparent in both directions. The mask is indicated with a red coloring by default.

Press Q again to leave Quick Mask mode and turn the mask into a selection. Only the top and the bottom regions will be selected, but not the bridge.

Lens blur

In order to achieve a natural-looking blur, click Filter/Blur/Lens Blur. Unlike Blur and Gaussian Blur, this filter imitates the blurring of a real optical lens, which helps maintaining the feeling of photographs.

On the top of the appearing dialog, you can first enable preview, then you can select whether it should be Faster (and less precise) or More Accurate. Next, you can see the Depth Map settings. As we have already created a quick mask, we won’t be needing them now. Anyway, Transparency and a previously created Layer Mask can also be used as depth maps. This setting enables you to control the focal distance of sharpness (that is, determine which areas will be sharp) with the Blur Focal Distance slider. In this example, we won’t be needing this either as we have already determined the sharpness plane (in the line of the bridge).

The Invert option is available, though. It inverts selection and thus makes the bridge blurred while leaves other areas sharp. Let’s leave it untouched for now.

Iris settings are much more important for us. You can specify the Shape of the iris. The more blades it has, the softer the blurred areas will look. An iris with few blades (such as Triangle (3)) produces sharper blurs. Radius controls the extent of blurring. We used a value of 15. Blade Curvature also affects sharpness. More curved blades result in softer blurring, so the softest result is achieved by using an Octagon (8) Shape and 100% Blade Curvature. We wanted a bit sharper background, so we used Pentagon (5) with a 0% setting. Rotation of the iris affects the placement of blurred blots in a small extent.

The Specular Highlights region controls the strength of lighter blots. Brightness is an obvious setting. Threshold specifies how much of the lighter blurred areas will be affected by it. A setting of 255 will result in ignoring these sliders. Low values  make the lighter areas strongly stand out of the blurred background. We didn’t need to use these options.

The last region adds Noise to the blurred areas. Amount specifies the extent of noise, and Distribution its type (Uniform or Gaussian). Select Monochromatic for single-colored noise. We didn’t need any noise in this example, so we left Amount at 0.

A mock-up town

Hopefully the result looks like a model city. As this kind of blur can only be achieved with traditional lens when photographing small objects from very near, the city panorama should look like a mock-up.