Selectively blurring an image can help your viewer find a focal point. Photoshop offers a realistic lens blur that also produces depth-of-field blurring. This allows some objects to be in focus while others fall out of focus. You can be very specific in regard to the blurring if you make an accurate alpha channel to serve as a depth matte. The depth matte defines how far away things are from the camera. Black areas in the alpha channel are treated as being the foreground, whereas white areas are seen as being in the distance.
1. Close any open files, and then open the file Lens Blur.tif (available here downloadable ZIP archive)
2. An alpha channel has already been added to the image. It was created using the Calculations command and Quick Mask mode.
3. Make sure the RGB composite channel is selected.
4. Choose Filter > Blur > Lens Blur to run the Lens Blur filter.
5. Choose the alpha channel from the Source menu. You can click the Invert box if you need to reverse the blur. For faster previews, choose Faster. When you’re ready to see the final appearance, select More Accurate.
6. Adjust the Iris shape to curve or rotate the iris. Photoshop mimics how a traditional lens operates. Even if you are not an experienced photographer, you can twiddle and adjust as desired.
7. Move the Blur Focal Distance slider until the desired pixels are in focus. Additionally, you can click inside the preview image to set the Blur Focus Distance.
8. You can add Specular Highlights by adjusting the Threshold slider. You must set the cutoff point for where highlights occur. Then increase the highlights with the Brightness slider.
9. Finally, it’s a good idea to add a little noise/grain back into the image. Normally, the blur obscures this, but putting it back in makes the photo seem more natural as opposed to processed.
Be sure to also check out the book and video training bundle —
Understanding Adobe Photoshop CS6: The Essential Techniques for Imaging Professionals