You've removed a background, placed the subject on a new colour, and there it is: a thin light (or dark, or green) outline around the edges. Here's why it happens and how to get rid of it.
Why halos happen
Edge pixels are a mix of subject and background. If a tool only decides which pixels to keep and doesn't correct their colour, those edge pixels still carry the old background's tint. On a background of a similar colour you won't notice. On a contrasting one, you get a halo.
Fix 1: Use a tool that decontaminates edges
Some background removers estimate the true colour of every edge pixel and remove the old background's tint. RemovingBackground.io does this on every image, which is why cut-outs shot against green hedges don't glow green on white. Try your image on the background remover.
Fix 2: Start with a better photo
- More contrast between subject and background
- Even lighting (strong backlight creates bright rims)
- The original file, not a compressed copy
Fix 3: Choose a closer background colour
If you're stuck with a particular image, a new background with a similar brightness to the original hides small halos.
Fix 4: Manual clean-up
In a design tool, you can shrink the mask by a pixel ("contract" or "choke") and soften it slightly. This trims the fringe at the cost of a tiny bit of edge detail. Use it on solid objects, not hair.
How to spot halos before you publish
Put the cut-out on pure black, then pure white. Zoom to 100% around the edges. Whatever you see there, your audience will see on the final design.
FAQ
Why do I get a white edge on dark backgrounds?
The original background was light, and its colour remains in edge pixels. Edge decontamination fixes this.
Is a halo the same as leftover background?
No — leftover background is whole chunks that weren't removed. A halo is a thin coloured edge around a correct outline.
