How To Blur The Background In Affinity Photo

by Dec 13, 2023Photo Editing Tutorials

Robin Whalley Landscape Photographer

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How To Blur the Background in Affinity Photo

In this tutorial, we look at three steps to blur the background of a photo using Affinity Photo. The starting image below features two people against a slightly blurred background. We will use the tools in Affinity Photo to separate the people from the background. This will allow us to add blur to the background without affecting the people.

Starting image showing two people against a background that we want to blur

Let’s look at the first step.

Step 1: Select the People in the Photo

We will use the Selection Brush Tool in Affinity Photo to make a rough selection of the people. Affinity Photo has many tools we can use to make a selection, but the Selection Brush is a good starting point. You will find it in the Tools Palette on the left of the Photo Persona interface.

The Affinity Photo Selection Brush Tool and Controls

After clicking the Selection Brush icon in the Tools Palette, its controls appear in the Context Sensitive Toolbar. The most important option to use is “Snap to edges”. This causes the selection to snap along any edges as you paint. It will produce a reasonably accurate selection and do most of the work for you.

To the left side of the controls are two icons. These will switch the tool between adding to and removing from a selection. Choose the Add icon (left) first to create a selection. Then, if you need to remove any areas from the selection, click the Subtract icon. You can then paint over the unwanted area to remove it.

You will see an animated dotted line around the selected area as you paint. We often call this line the marching ants. You can see it indicated in the following screenshot.

Selection of the two people in the photo

Having created an initial selection, it’s time to refine it to improve the accuracy. You can do this by clicking the Refine button in the Context Sensitive Toolbar.

Refining the Selection Edges

After clicking the Refine button, the selection is converted to a mask, and the Refine dialog opens.

Using the Brush Tools in the Refine dialog to improve the accuracy of the selection

You can now magnify the image to check along the edges of the mask. If you find an area that isn’t accurate, use the Adjustment Brush tools in the Refine Selection dialog to fix them. You can learn more about how to work with these in my tutorial on the subject.

After creating an accurate selection of the people in the photo, it’s a good idea to save it in case we need to return to it again. The best way to do this is to save it as a spare channel in the image. Choose “Save Selection” and “As Spare Channel” in the Affinity Photo Select menu.

You should now see the new Spare Channel at the bottom of the Channels Studio Panel.

Step 2: Separate the People from the Background

Having created our selection, we can use it to separate the people from the background in the photo. We do this so that the people in the photo aren’t blurred when we blur the background. This avoids creating a halo around them.

Duplicate the Background layer by right-clicking it in the Layers Studio Panel. Then, in the popup menu, select the Duplicate option.

Duplicating the image layer in Affinity Photo's Layers Studio Panel

You should now see the duplicate layer. I like to rename this Foreground to distinguish it from the Background layer. You can then hide the new Foreground layer by clicking the visibility switch to the right of the layer.

We can now use our selection to remove the people from the Background layer.

When doing this, it’s a good idea first to expand the selection to ensure you don’t leave an edge around what’s been removed. Click the Grow/Shrink option in Affinity Photo’s Select menu to open a dialog with a single slider. Move the slider left or right to grow or shrink the selection.

Growing the Pixel Selection in Affinity Photo

Here, you can see the slider has been moved right to expand the selection around the people.

With the selection expanded, we can choose the “Inpaint” command from the Affinity Photo’s Edit menu. This will remove the people, replacing them with a similar background.

Using the Inpaint command in Affinity Photo to remove the people from the photo

Don’t worry that this looks messy. Most of it will be hidden, and what isn’t will be heavily blurred.

You can now clear the selection by choosing Select then Deselect in the Affinity Photo menu.

Removing the Background in the Foreground Layer

The next stage of this step is to remove the background from the top Foreground layer.

Click the visibility icon for the Foreground layer to make it visible again. Then, click the layer in the Layers Studio Panel to ensure it’s selected.

In the Channels Studio Panel, right-click on the Spare Channel you saved earlier. In the popup menu, choose the “Load to Pixel Selection” option. You will then see the marching ants of the active selection appear around the people.

We then need to invert this selection so that the background is selected rather than the people. You can do this in the Select menu by choosing the “Invert Pixel Selection” option. Having done that and with the Foreground layer selected in the Layers Studio Panel, press the delete key on your keyboard. This will delete the selected background area from the layer. You can check it by hiding the Background layer in the Layers Studio Panel.

Foreground Layer with the background removed

You can now see the background in the photo replaced by a checked pattern, indicating the area is transparent.

Clear the pixel selection by choosing the Deselect option in the Select menu.

Step 3: Apply a Blur to the Background

We are ready to blur the background in our Photo using Affinity Photo’s Gaussian Blur filter. If the Background layer is hidden, make it visible again before continuing.

Click the Background layer in the Layers Studio Panel once to ensure it’s selected.

Using the Affinity Photo Layer menu, choose “New Live Filter Layer”, then “Blur” and “Gaussian Blur…”. You should see the new Live Filter added to the Background layer in the Layers Studio Panel and a Blur dialog appear.

Blurring the background in the photo using the Affinity Photo Gaussian Blur filter

Move the Radius slider right in the dialog until you achieve the desired blur.

Because we have used a Live Filter and not a regular Filter, we can continue to open the Gaussian Blur dialog to adjust the blur level. We can also hide the Live Filter to remove its effect from the image.

Here’s a comparison of the photo with the background blurred, next to the original.

Image with blurred background compared to the original

The key to blurring the background in a photo is being able to make an accurate selection of the area you don’t want to blur. That wasn’t too difficult with this photo, but sometimes you need to select something set against a busy background. In this article, I explain how to cut out a subject on a busy background using Affinity Photo. It would be a helfpul one to read next.

More Affinity Photo Tutorials

You’ll find more high quality, free tutorials on my Affinity Photo Tutorials page.

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