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Post-production: Increasing the depth of field in Adobe Photoshop

From our digital-only Photography Magazine, we look at how to increase the depth of field in post-production

Post-production: Increasing the depth of field in Adobe Photoshop

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Portraits can often work well if the background is pleasingly out of focus, so as not to distract from the subject. There are a number of times, though, when this mightn’t be possible. If the subject is relatively close to the background, or if you’re shooting with a camera that has a smaller than full-frame sensor, or if you’re shooting with an aperture that’s too small (giving a greater than required depth of field), then the background can be too in focus. Luckily, though, this can be quickly fixed using Adobe Photoshop.

This technique of increasing the blur of the background of an image uses the comprehensive image selection tools of Adobe Photoshop — notably the quick mask function, which allows for a detailed selection to be made, and edited, without the risk of accidental deselection.

Creating a mask
The first stage is to use one of the quick selection tools, such as the Lasso Tool (L), to create a rough selection around the subject of the picture. This will subsequently be refined, so it doesn’t have to be too accurate. Next, click on the Quick Mask tool (Q) to create an editable red mask over the non-selected areas.

This quick mask can be edited using the painting tools. Using the Brush tool will add to the red mask; using the Eraser tool will delete from the red mask. You can change the size and shape of the brushes in each instance; use a large brush to cover large areas or use a smaller brush for finer details. Zoom in and work at 100% magnification when you’re at the edges of your subject for a more accurate result.

One of the brush adjustments that can be made is to soften the edges of the brush, creating a more feathered selection. As you should be creating a hard edge between an in-focus background and a blurred background, a soft brush won’t be that useful in this instance.

Saving your selection
When you’ve finished the mask, you can then click on the Quick Mask tool (Q) again to come out of mask mode. This will then outline the selected area with the ‘marching ants’ moving outline. The non-masked areas will be selected.

You can refine the selection using the Select > Modify… menu, to then feather, shrink, smooth or expand your selection.

At this point, it’s a good idea to save your selection. Go to the Selection > Save Selection… menu item, and give this selection a name. Make sure to also save the document you’re working on.

Create a new layer
With the selection active, choose Edit > Copy and then Edit > Paste in Place. This creates a new transparent layer exactly matching the position in the original image. The original image will be automatically placed in a layer called Background.

Layers are a great way to work on complicated images, as each element can be on a separate, editable layer. This means that you can work on a part of the image at any time without affecting other elements on other layers. Layers also make it possible to revisit an image at any time, making edits and corrections and even removing elements from the image.

The way to visualise layers is to imagine that any elements would be on a sheet of clear plastic. Any of these sheets can be viewed and edited on their own, but if viewed as a whole, the entire image can be viewed as a single entity.

You can also add adjustment layers, so that things like Brightness/Contrast, Levels and Colour Balance can be applied through a layer that will only affect elements on layers beneath it. These can be changed or even removed at any point, and give considerably more control than applying these tools to a whole image.

Blurring the background
In the Layers palette, an eye logo can be seen next to each layer. This toggles the layer as being visible or invisible. In this example, having the subject visible will help you to assess how well the blurred background will work with the image.

Click on the Background layer to make it active. Now, any filters or tools that you use will be applied only to the background image, and not to any other parts of the image.

To work on a different layer, you just need to click on that layer to activate it.

From the Filter Menu, select Blur > Gaussian Blur. In the pop-up window, drag the Radius slider to increase or decrease the amount of blur on the background. Because you’re working on the Background layer, the subject will be unaffected. When you’re happy with the result, click OK.

This technique works well if the background is a consistent distance away from your subject. If parts of the background are closer to the subject, they should be less blurred than the others for a more realistic result. You can fade the amount of blur using the Gradient tool on the background.

When you look at the final image, you’ll often see some slight lighter or darker fringing on parts of the subject. To remove these, click on the layer containing the subject (not the blurred background). Zoom in to at least 100% and then use the Eraser tool with a very small brush to refine the edges of the subject. As you erase the fringes, the blurred background will show through. As the background layer isn’t selected, the eraser tool won’t affect it.

 

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Published in issue 8 of National Geographic Traveller (UK) Photography Magazine