What causes posterization or banding in smooth skies during post-processing?
Asked 2/13/2020
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After editing a photo, the smooth gradient in the sky turned into visible bands with sharp borders, which looks like posterization/banding. Softening or reducing sharpness only blurred the edges of the bands and did not restore the smooth gradient. In one case, removing all edits one by one showed that a Lightroom adjustment brush was causing the problem, and the banding remained even when the brush sliders were set to zero until the brush itself was deleted. What should be checked first when this happens, and what typically causes this kind of artifact?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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Posterization was an intentional artistic enhancement. This was a darkroom technique used to create a relief image often used as an eye-catcher.
In modern time this term is applied to a defect also called banding. Banding occurs mainly in digital photography as bands of continuous tones in areas that should reproduce smoothly like blue sky etc. This artifact occurs mainly when the bit depth is insufficient to display a continuous gradation.
To save file space we often use file compression techniques. These work by casting out data in areas where the content is mundane (such as uniform sky or water).
Originally by user44949. Source · Licensed CC BY-SA 4.0
user44949
6y ago
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This artifact is usually called banding or posterization: smooth tonal transitions break into visible steps. The most common cause is insufficient tonal precision, often made worse by editing or compression, especially in low-detail areas like skies.
Based on the reports here, the first thing to check is any local adjustment, especially a Lightroom adjustment brush or mask. In this case, the brush itself caused the banding, and deleting it fixed the issue even when its sliders appeared to be set to zero.
More generally, banding can come from:
- limited bit depth in the image or editing pipeline
- heavy compression
- strong edits to smooth gradients
- local adjustment tools introducing artifacts
If you see it, disable edits one at a time, starting with local adjustments and masks. Also inspect export settings and file format, since compressed or low-bit files can make smooth skies break into bands.
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