There are tradeoffs that come with every photographic decision. For instance, choosing to shoot wide open for the benefits of shallow depth of field can also make it more likely to miss focus. So instead of shooting wide open, you choose ƒ/8 to ensure sharpness but then suffer through an image with too much detail in the background. This, like many photographic issues, can be improved with some careful post-processing. And while many folks claim there’s an easy way to create blurred backgrounds in Photoshop, they typically skip one crucial step that keeps their artificial blurs from looking quite natural. Here’s my secret to creating beautiful out-of-focus background blur (or bokeh) with just a few steps in Photoshop.
First, choose an image with a single, isolated subject. Portraits, for instance, tend to work well for this. (They also tend to be the ideal subject that can benefit from added background blur.) Open the image in Photoshop, then click Command+J (or CTRL+J on Windows) to duplicate the image onto a new layer, then do it again to create a second duplicate layer. Turn off the top layer by clicking the eye icon next to the top layer in the Layers palette, then click the middle layer icon in that palette so that the middle layer is active.
The secret to my approach’s success is in this additional layer and how you treat it. Some folks advocate simply selecting the subject, inverting that selection and then blurring the background—or even creating a new layer and blurring the one below, then using a mask to isolate the subject. The problem with both of these approaches is they create a fuzzy, blurred edge around the subject. It’s because some of those “subject pixels” blur too, and then unnaturally blend into the blurred background. That ghosted edge of subject blurring into the background is a dead giveaway that the bokeh isn’t optical but digital.
So I take that middle layer in Photoshop and then open the Liquify filter. Here, I select a large brush size (roughly as big as, say, the subject’s head) and I push the edges of my portrait to make her smaller. I’m not worried about making it look real, I just want to squeeze the subject into a smaller footprint so when her edges end up blurring in the background, they’ll be hidden by her unaltered form on the top layer. So just liquify the edges and make the subject slightly smaller. (In lieu of liquify, you could also use a clone stamp if you’re more comfortable with that approach.) The key is that you want the background of the image to encroach on the outline of the subject.
Next, click the top layer’s eye icon in the layers palette to reactivate it, and use the Select Subject command to automatically select the subject. Then use Select and Mask in the Select menu to refine the edges of the selection. (I actually prefer to hold the Shift key when I click Select and Mask, which opens up the legacy version of the Refine Edge tool.)
Simply paint along the edges of the subject and Photoshop will automatically go over the edge with a virtual “fine-toothed comb” to ensure the subject is selected and the background isn’t. Now with the edge cleaned up, the selection is very accurate around the subject, so click OK when you’re ready to move to the final step.
With the subject selected and the edges of that selection refined, click the New Layer Mask icon in the Layers palette to turn that selection into a mask on the top layer. Now you have the subject isolated on her own layer, so when you modify the background layer behind her she—and her edges—will remain tack sharp and unblurred.
Finally, once again click on the middle layer to make it active. (This is the one you had previously liquefied to encroach background onto the space previously occupied by the subject.) Make sure no selection is active, then use a Gaussian Blur filter found under the Blur heading of the Filter menu. You’ll need to do some experimentation to determine what amount of blur looks best to you, and there’s no right answer. It’s all a question of taste, though I will say this is often a good example of “less is more.” Regardless of the intensity of the blur, you’ll notice there’s no blurring of the subject creating a ghostly shadow around the edges of the isolated subject.
You may have to further refine the edge of the subject’s mask—which I do by simply painting any errant areas by using a paintbrush on the layer mask. In the end, what you’ll see is a photograph with a beautifully blurred bokeh background that looks just as authentic as if it had been made by shooting with a wider aperture in camera.