How to Check Your Screen for Colour Banding
Colour banding is visible stepping in what should be a smooth gradient, caused by too few distinct levels somewhere in the display chain. The panel, the signal format, the cable bandwidth and the content itself can each be the limiting factor.
Where the levels are lost
A smooth gradient needs many distinct intermediate values. If any link in the chain cannot carry them, the gradient collapses into visible steps. That link might be the panel's bit depth, the colour format the signal is using, the bandwidth available over the cable, or compression baked into the content before it ever reached your machine.
This is why banding is worth diagnosing rather than assuming. A panel blamed for banding is frequently fine, and the actual limit is a cable running at the edge of its capacity or a graphics setting left at a reduced depth.
Looking in the right place
Dark tones reveal banding first. The steps between adjacent levels are proportionally largest in shadow, so a gradient that looks smooth in its bright half often bands visibly in its dark quarter. Check there before concluding a display is clean.
Step back from the screen. Banding is frequently easier to see at a distance, because your eye stops resolving individual pixels and starts seeing the boundaries between regions.
Compare against a deliberately stepped pattern. Having an unambiguous example of banding on screen calibrates your judgement about the smooth gradient next to it.
The bandwidth trade
Resolution, refresh rate and colour depth all consume the same finite bandwidth over a display cable. When you raise one, something else may quietly drop. Colour depth is usually first to be reduced, which is why banding often appears immediately after enabling a higher refresh rate.
If banding appeared after a change, reverse the change to confirm the cause, then look for a cable explicitly rated for the combination you want. A cable that carries your resolution at 60Hz may not carry it at 144Hz with full colour depth.
Panel limits versus everything else
Many displays sold as 10-bit are 8-bit panels using dithering to approximate the extra levels. Dithering is a legitimate technique and works well, but it does not always match a true 10-bit panel, and a marketing figure is not a guarantee of smooth gradients.
If banding appears in one application but not others, the display is not the problem. Compressed video in particular bands in skies and shadows regardless of how good the screen is, because the levels were discarded during encoding.
Test it yourself: Gradient Test
Frequently Asked Questions
What causes colour banding on a monitor?
Too few distinct levels somewhere in the chain — the panel's bit depth, a reduced colour format, insufficient cable bandwidth, or compression in the content. The gradient cannot be drawn smoothly if the intermediate values do not exist.
Is banding always a fault?
No. Faint banding in the darkest part of a gradient is common and usually normal. Obvious banding across a whole gradient points to a setting, a cable or a genuinely limited panel, and the first two are worth checking before blaming the third.
Why did banding appear after I raised my refresh rate?
Because resolution, refresh rate and colour depth share the same cable bandwidth. Raising refresh rate can push the link past what it can carry, and colour depth is usually what gets reduced to fit.
Will a 10-bit monitor remove banding?
It reduces it considerably, but many displays marketed as 10-bit are 8-bit panels with dithering. Content and cable bandwidth still matter, so a 10-bit panel fed a bandwidth-limited signal can still band.
Is banding the same as posterisation?
They describe the same visual result. Posterisation usually refers to the effect being present in the source content, and banding to the effect introduced by the display chain.
Sources: MDN — Fullscreen API
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