Glossary
Colour Depth
Also: bit depth · colour depth (bit depth)
Colour depth is the number of bits used to store each pixel's colour. 8-bit holds 256 shades per channel — about 16.7 million colours total; higher depths store more shades, reducing visible banding in gradients.
Reviewed by Chad Solomon · Updated June 2026
Explained
How bit depth is measured
Colour depth counts bits per colour channel. Standard 8-bit images use 8 bits each for red, green, and blue — 24-bit total, giving 16.7 million colours. Adding an alpha channel makes 32-bit. Professional formats like TIFF support 16 bits per channel for finer gradients.
Explained
Banding and indexed colour
Too few colours cause banding — visible steps in smooth gradients like skies. GIF and 8-bit indexed PNG store a palette of at most 256 total colours, which suits flat graphics but bands on photos. Full-colour (truecolour) formats avoid this.
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Questions
Frequently asked
- What is 8-bit colour depth?
- 8-bit colour depth stores 256 shades per channel. Across red, green, and blue that produces about 16.7 million colours, the standard for JPG, PNG, and WebP.
- Why do gradients look banded?
- Banding appears when an image has too few colours to render a smooth gradient, common in 256-colour GIF or indexed PNG. A full-colour (truecolour) format fixes it.
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