Mistaking the coloured rim left by a background removal for lens fringing; one comes from the mask, the other from the optics.
Editing and retouching
Chromatic aberration
Also called colour fringing, purple fringing or ca. Here is what it means, when it changes what you export, and what people get wrong.
Editing and retouchingRuns on your deviceUpdated 10 August 2026
The short answer
Chromatic aberration is a lens fault where different wavelengths of light do not come to focus in the same place, leaving coloured outlines along high-contrast edges. It usually shows as purple, magenta, green or cyan fringes, and it is worst at wide apertures, towards the corners of the frame, and around backlit or shiny edges.
Updated
The short version
Chromatic aberration at a glance
| Quick fact | Detail |
|---|---|
| Also called | Colour fringing, purple fringing |
| Cause | A lens focusing wavelengths differently |
| Lateral type | None at the centre, grows towards the corners |
| Longitudinal type | Everywhere in frame, worst wide open |
| Best fix | Lens profile correction on a RAW file |
| Makes it worse | Sharpening, upscaling and heavy compression |
Slide the table sideways to see every column.
What is the difference between lateral and longitudinal fringing?
Glass bends short wavelengths more than long ones, and that single fact produces two distinct faults.
Lateral chromatic aberration, also called transverse, is a difference in magnification between colours. The red and blue versions of the image are slightly different sizes, so they line up perfectly at the centre of the frame and drift apart towards the corners. You see red and cyan, or blue and yellow, opposing fringes that grow with distance from the middle. Because it is a geometric mismatch, software can correct it well by rescaling the colour channels against each other, which is what a lens profile does.
Longitudinal chromatic aberration, also called axial, is a difference in focus distance between colours. It is present everywhere in the frame including the centre, and it typically shows as a purple cast on edges slightly in front of the focus plane and a green cast on edges slightly behind it. It is worst wide open and reduces sharply as you stop down, but it is much harder to fix afterwards because the colours are genuinely out of focus rather than merely misplaced.
Why is a coloured cut-out edge not chromatic aberration?
They look superficially alike and they have nothing in common, so the fixes do not transfer.
- Lens fringing is baked in at capture. It follows the optics: absent or weak in the centre for the lateral kind, strongest on high-contrast boundaries, and it uses opposing colour pairs, so one side of an edge leans purple while the other leans green.
- Cut-out fringing is a masking artefact. When a subject is separated from its background, the pixels along the boundary are mixtures of subject and background colour, and if the matte keeps them the old background bleeds through. A garment shot on a green backdrop comes back with a green rim; the same garment shot on grey comes back with a grey rim.
The tell is consistency. A cut-out halo is one colour, it matches whatever the original background was, and it traces the whole outline evenly wherever the subject sits in the frame. Lens fringing changes colour depending on which side of the edge you look at and gets stronger towards the corners. Fix the first by refining the matte, decontaminating the edge colour or eroding the mask by a pixel; fix the second with a lens profile or a defringe control.
How much does fringing matter for product photos?
More than it seems, because product photography is full of the conditions that provoke it: chrome and polished metal, glassware, jewellery, watch bezels, dark items against a bright white sweep, and backlit packaging. A purple line along the edge of a watch case is small on screen and unmistakable once a buyer opens the zoom view.
It also compounds with everything you do next. Sharpening treats the fringe as an edge and strengthens it, upscaling turns a one-pixel line into a four-pixel band, and JPEG chroma subsampling smears the colour sideways so a later defringe pass has less to grip on. A coloured rim on the subject boundary is also one more thing for a background removal model to misread. Correct fringing early, ideally on the RAW file with a lens profile, before any sharpening, upscaling or cut-out work.
What people get wrong about chromatic aberration
Each one is a real failure mode, not a style preference.
Sharpening before removing fringes, which strengthens the coloured edge and makes it harder to clean up.
Shooting wide open for a blurred background and then wondering why every bright edge carries a purple outline.
Applying a global desaturation of purple to kill fringing, which drains the colour from genuinely purple parts of the product.
Questions people ask
Chromatic aberration, answered
The follow-up questions people search for once they have the definition.
What causes purple fringing on photos?
Usually longitudinal chromatic aberration, where the lens focuses blue and violet light at a slightly different distance from the rest. It shows on high-contrast edges just in front of the focus plane, is strongest at wide apertures, and is common around backlit branches, chrome trim and bright reflections.
Can chromatic aberration be removed?
Lateral fringing corrects very well, since it is a scaling mismatch between colour channels that a lens profile can undo. Longitudinal fringing is harder because the affected colours are genuinely out of focus, so a defringe tool suppresses the colour rather than restoring the detail underneath.
Does stopping down the aperture help?
It helps a great deal with longitudinal fringing, which often disappears within two or three stops from wide open. It does very little for lateral fringing, because that comes from magnification differing between colours, which the aperture does not change.
Why does my cut-out have a coloured edge?
That is almost always colour contamination from the original background rather than a lens problem. Edge pixels blend subject and background, so a leftover rim matches whatever you shot against. Refining the matte or shrinking the mask by a pixel fixes it; a defringe tool will not.
Same cluster
More from the glossary
Neighbouring entries, so every term in the set is one hop from every other.
Clipping path
A clipping path is a vector outline drawn around a subject so that everything outside the line is hidden.
Chroma subsampling
Chroma subsampling stores colour information at a lower resolution than brightness, because human vision resolves fine detail in brightness far better than in colour.
CMYK
CMYK is the four-ink colour model used in printing: cyan, magenta, yellow and key (black).
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