How to Apply the Lens Blur Filter in Photoshop CS6
If you use a Lens Blur filter on an alpha channel in Photoshop CS6, the alpha channel acts as a depth map, imitating the depth of field created by the aperture on the camera. Depth of field relates to the plane of focus or how in-focus the foreground elements are when you compare them to the background elements.
The approach of using the Lens Blur filter is great for taking a fully focused image and creating a shallow depth of field in which the foremost object is in focus and the background elements get blurrier the farther they are from the focal point.
You can achieve this effect by creating an alpha channel filled with a white-to-black gradient — black where you want the most focus, white where you want the least focus or most blur.
Here’s a brief description of setting the Lens Blur filter options:
Source: If you have an alpha channel, select it from this drop-down menu (pop-up menu on the Mac). The Lens Blur option interprets the various grayscale values of the alpha channel and applies the blur according to the value set in the Blur Focal Distance option.
Choose Transparency to make an image get blurrier while it gets more transparent. Choose Layer Mask to apply the blur according to the grayscale values on the layer mask. If your image contains none of these options, choose None. Photoshop applies the blur on the image.
Blur Focal Distance: Specifies how blurry or in focus an area of the image is. Drag the slider to specify the value or click the crosshair cursor on the part of the image that you want to be in full focus.
Iris: The Iris settings are meant to simulate a camera lens. Specify the shape of the lens, as well as the radius (size of the iris), curvature, and rotation of that shape.
Specular Highlights: The Lens Blur filter averages the highlights of an image, which, if left uncorrected, cause some highlights to appear grayish. These controls help to retain specular highlights, or those highlights that should appear very white. Set the Threshold value to specify which highlights should be specular (remain white). Set a Brightness value to specify how much to relighten any blurred areas.
Noise: Blurring, of course, obliterates any noise (or film grain) that an image may have. This absence of noise can cause the image to appear inconsistent or unrealistic, in many cases. Drag the slider to add noise back into your image. Choose monochromatic to add noise without affecting the color.