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Do you see your photo and wish the subject stood out a bit more? Does your photo look somewhat flat? Or maybe the background has people or objects that are unappealing? All of these can be fixed with one simple thing: a shallow depth of field.
In this tutorial, you will learn how to achieve this in post-production using Photoshop.
Let’s start by clarifying that depth of field is the area of your photograph that is in focus, it’s also called focus range. There are three factors that affect your depth of field.
First is the aperture or f-number. The smaller the number, the smaller the focal range and vice versa, so f/5.6 will have a shallower depth of field than f/22. The second and third factors are very linked together; the focal length and the distance to the subject.
If you are using a telephoto lens and you can, therefore, stand farther from the subject you’ll have a shallower depth of field than standing closer with a wide-angle lens. You can learn more about this relationship and its effect on depth of field in my previous tutorial, How to Use Still-life Subjects to Understand Focal Lengths.
However, if you didn’t manage to set up these things when you were shooting, or you still need more (blur in the background) you can also fake the effect of shallow depth of field in post-production. Here are two techniques to do it using Photoshop.
With your image already opened in Photoshop, start by duplicating the layer by going to Menu > Layer > Duplicate Layer, then make the canvas bigger. You can do this by going to Menu > Image > Canvas Size.
It doesn’t matter the size of the canvas or the direction because you’ll be cropping it later. However, it’s important that there’s enough room for your main subject to be dragged into it on the next step.
Then select your subject. It doesn’t have to be precise so you can simply use the Lasso tool and draw a selection around it. Now change to the Content-Aware Move tool which you’ll find hidden behind the Healing Brush on the tools panel. Next, drag your selection out of the image into the empty canvas size that you created before.
Once you drag it out, Photoshop’s algorithm will fill the space you’re leaving empty with the information from the surrounding area. If you skip this step and blur the background with the subject still on it, the colors will spill out so it’s important that you do this part.
Now you can crop out the extra background, including the subject you dragged out and change the canvas back to its original size. Your background is now ready for you to blur it. Go to Menu > Filter > Blur > Field Blur. When the blur applies, a wheel appears in the center with a percentage on how strong the blur is. Adjust it to your liking.
With this blurred layer still selected, add a layer mask to it by clicking on the button that looks like a rectangle with a circle in the middle on the bottom of the Layers Panel. Then paint on the mask with a black brush, over the subject you want to keep sharp from the original image.
The part that you painted black is now transparent so the layer beneath it, which is your original image will be visible. Finally just flatten your image and you’re done!
The technique you just learned is very useful if your subject is separated from the background, but what happens if you want a shallower depth of field because the objects are closer together? Or because it’s the same subject but you only want a part of it in focus?
In these cases, you need to create an effect that is graduated (fades from one end to the other). To do this here is another technique.
First of all, you need to duplicate the layer by going to Menu > Layer > Duplicate Layer like you did in the previous example, or use the shortcut by dragging the background layer into the Duplicate layer button on the bottom of the panel (or hit Ctrl/Cmd+J).
Then apply a Layer Mask to the new layer by clicking on the mask icon. Inside the mask, you will use the Gradient tool to mark where you want the sharp areas. In this case, I used the circular one but you can use a linear one or whichever is best for your image. I turned off the background layer so you see what I mean.
Now go to Menu > Filters > Blur > Lens Blur and a new window will pop-up. Here you’ll see your image with the filter applied and a panel for adjustments on the right side.
It’s important that you set Layer Mask as the source, that way the gradient selection that you did before is what will determine how the filter gets applied.
Once you do that, the Blur Focal Distance slider will be enabled and you can start adjusting it to your liking. I also adjusted the radius and blade curvature, but you should move all the settings to get a feeling for the effects until you’re satisfied.
Hit OK to apply and flatten the image to finalize the result. That’s it!
Remember that every image will need a different treatment to look realistic because there are many things that determine the depth of field so keep experimenting and show us the results in the comments section.