Digital signal and image processing
Explainer
Bit depth: why 8 bits gives 256 grey levels
Guess how many grey shades one 8-bit pixel can show.
Quick check · tap an answer to continue
Lesson notes
Key points
- Sampling decides where you measure; quantisation decides which value you round each measurement to.
- With b bits per sample, you get two to the power b possible levels.
- So an 8-bit greyscale pixel runs from 0 for black to 255 for white.
- Too few bits and smooth shading breaks into visible bands, an artefact called false contouring.
Definitions
- Quantisation
- Mapping each continuous sample amplitude to the nearest of a finite set of discrete levels.
Takeaway: Bits set the levels: L = 2ᵇ; too few causes false contouring.
Quick check: How many grey levels can a 4-bit image represent?
- 8
- 16
- 32
Levels equal 2 to the power of bits, and 2⁴ = 16.
QuantisationLevels = 2^b256 levelsFalse contouring
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