Posterization is the close cousin of banding: when there are too few tonal levels to represent a smooth gradient, the continuous range flattens into a small set of discrete bands of constant tone, the way a poster printed with a reduced palette renders a photograph in a handful of flat colors. It shares banding's two roots - too low a bit depth (few code values per channel) and coarse quantization that rounds away the faint variation carrying the gradient - and lives in the same place, the smooth regions like skies, fades, and flat color fills, where the eye locks onto the abrupt steps between levels (amplified by the Mach-band effect). Like banding, posterization is a tonal-quantization artifact the popular full-reference metrics are nearly blind to: the per-pixel error of a flattened level is tiny, so PSNR, SSIM, and legacy VMAF under-report it, and a no-reference vision-based detector such as CAMBI is the right tool. The fixes are the same - higher bit depth, dithering, or a debanding filter.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
Posterization flattens smooth gradients into a few flat bands and slips past PSNR, SSIM and VMAF, so it needs its own check. We wrote seven volumes covering the whole video stack, and for posterization start with Volume 1: bit depth, 10-bit encoding, quantization, banding and HDR. Written by Nikolay Sapunov, CEO at Fora Soft.
Seeing posterization in gradients after encoding or color conversion?
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