What causes white halos around subjects against a bright background?
Asked 7/26/2023
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I sometimes see a white outline or halo around a subject, especially when the subject is against a bright background like the sky. In other parts of the image, or when the background is similar in tone, the halo is not visible. Is this caused by lens refraction/zooming, or is it more likely from post-processing?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
2y ago
2 Answers
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It is not due to the lens.
For there to be anything discernable there must be contrast (color/brightness). And anything done to increase visibility (sharpness/clarity/dehaze/etc) is some form of increased contrast.
This particular example is characteristic of low level (large detail) sharpening... if it was a raw file it was done in pos. If it was recorded as a jpeg it could have been done at any point, but this degree of artifact is more typical of post editing. Understand that any image must undergo "editing" in order to be a visible image created from raw sensor data.
The primary clue here is that the contrast increase has created a light halo along dark edges, but also a dark halo (outline) along light edges.
You do not see the halo at point B because there is not a constant level of contrast along that edge... i.e. it is lost in the BG texture/details.
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
2y ago
0
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This is most likely a sharpening artifact, not a zoom or lens-refraction issue.
White halos around dark edges against a bright background are a classic result of contrast-enhancing edits such as sharpening, clarity, dehaze, or similar processing. Many sharpening methods work by increasing edge contrast, which can create a bright halo on one side of an edge and a dark halo on the other. It shows up most clearly where there is strong contrast, such as a dark subject against a bright sky.
That also explains why you may not see it everywhere: if the background is similar in brightness or color to the subject, the halo is much less noticeable.
If the image came from a RAW file, this was almost certainly introduced during processing. If it is a JPEG, it could have been added in-camera or later in editing, but strong visible halos are especially typical of over-sharpening in post-production.
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