Infographics / Digital Radiography

Analogue vs Digital Signal & ADC Quantisation

A continuous analogue signal is sampled at a fixed spatial pitch (pixels) and quantised into discrete grey levels, producing a staircase digital output snapped onto a grid. The spatial sampling pitch sets the pixel size and Nyquist limit, while the number of bits sets the number of grey levels (2 to the n). A grey-scale ramp compares fewer bits (coarse, banding) with more bits (finer grey-scale).

Analogue-to-digital conversion of an image signal A continuous analogue signal is sampled at a fixed spatial pitch (pixels) and quantised into discrete grey levels, producing a staircase digital output snapped onto a grid. The spatial sampling pitch sets the pixel size and Nyquist limit, while the number of bits sets the number of grey levels (2 to the n). A grey-scale ramp compares fewer bits (coarse, banding) with more bits (finer grey-scale). Analogue-to-digital conversion (ADC) sampling in space (pixels) + quantisation in amplitude (grey levels) grey level (amplitude) digital: sampled + quantised analogue: continuous signal quantisation (amplitude): n bits → 2ⁿ grey levels 8-bit = 256 levels (often too few) typical DR / DICOM: 10–16 bits one pixel = sampling pitch Δx spatial detail set by the Nyquist frequency = 1 / (2 × pixel size); finer pitch → higher resolution more bits → finer grey-scale (better contrast resolution) fewer bits (coarse, banding) 2-bit: 4 grey levels more bits (finer grey-scale) 4-bit: 16 grey levels
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