Blur Image Background in Affinity Photo

While the ultimate goal is to blur the background of an image, I also want to save the outline that I’ve drawn around the main object in case I want to alter it later or just have it handy for future use.

1. Selection Brush Tool: draw marching ants around main subject

  • Mode: Add (toggled between Add and Subtract if the selection got in or out of the target outline)
  • Width: (large to begin with, then used smaller brush sizes to accommodate finer details)
  • Snap to edges: On
  • Soft edges: on (might leave this setting un-ticked next time)

2. Save selection: Select > Save Selection > As Spare Channel

3. Save file (marching ants selection has now been saved as a Spare Channel in the Channels Panel

4. To add Gaussian Blur to background we’ll first load the pixel selection from the shape previously saved to the Spare Channel:

  • In the Channels panel press ^(ctrl)-click in the tiny gap between the thumbnail of your shape and the Spare Channel text, then
  • Select Load to Pixel Selection in the pop-up dialog window
  • Source: Affinity Help “Pixel selections from channels” > Section titled “To create a pixel selection from a channel”)

5. Then Invert pixel selection (so the marching ants are around the background and not the main subject): Select > Invert Pixel Selection

6. And finally add Gaussian Blur via a Live Filter Layer: Layer > New Live Filter Layer > Blur > Gaussian Blur…

  • Preserve Alpha: On
  • Radius: 26px
  • Opacity: 100%
  • Blend Mode: Normal
  • Then exit dialog window by ticking the red dot in upper-left corner of dialog window

7. Save file

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