Color banding

Banding is arithmetic, not a bug. An ordinary screen stores eight bits per channel, so there are 256 values available between black and full intensity and nothing in between them. Take a gradient from #2B3566 to #0D1024: the blue channel travels from 102 to 36, which is 66 distinct values, and if that ramp is 600 pixels tall then each value has to hold for about nine pixels. Nine pixels of one flat colour beside nine pixels of another is a stripe, and the eye is extremely good at finding it. The name for the same thing in image editing is posterisation, and in video work it is usually called contouring.

Two conditions make it worse, and they arrive together. The shallower the transition, the fewer values it has to spend, so a subtle ramp bands harder than a dramatic one. And the larger the area, the more pixels each value has to cover. That is why banding shows up almost exclusively in the same places: dark hero backgrounds, near-flat overlays across a full page, blurred backdrops, and any mesh gradient, which is mostly shallow transitions over a lot of room. Compression compounds it, because JPEG and most video codecs actively flatten low-contrast regions into blocks of one value.

The cure is dithering: add fine noise so neighbouring pixels sit on either side of the step and the eye averages them back into the colour that was missing. That is what a grainy gradient is doing, and why the fix for banding is grain rather than blur, which only smears the same stripes. Two other levers help. Blending in a wider space, or simply letting the hue drift a little across the ramp, gives the transition more values to spend than a single channel had. And rotating the gradient a few degrees off the pixel grid breaks the perfectly horizontal edges the eye locks onto.

Judging it honestly is harder than fixing it. Your own display is part of the system: many laptop panels are six bits per channel with temporal dithering on top, some scaling and colour management paths quantise a second time, and a screenshot can add banding that the live page did not have. That is why the specimen here builds its stripes deliberately, with hard stops, rather than hoping a shallow ramp misbehaves on your machine. If a client reports banding you cannot see, believe them and reach for grain.