Colour Science & Perception
what the eye settles, and what it cannot
Concept

Black point compensation — where it appears

A rescaling of lightness that maps a source's darkest reproducible colour onto a destination's. Nothing in the shadows is clipped, and everything else moves a little to make room. The destination's black is measured; the source's is usually stated, which makes the larger term the one nobody checks.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

What happens to a tone the destination cannot print. Source lightness along the bottom, destination lightness up the side, for a print whose black is L* = 8. Clipping is the flat segment on the left — 4 of 10 levels in the bottom twenty points of the scale arrive as the same number, and nothing downstream can recover them. Black point compensation is the straight line: all 10 levels survive as different numbers, and every tone in the picture has moved to pay for it.

A black that is not black

The deepest colour a four-colour press can make is L* 2.4, and against its own paper that is a contrast of about 320 to 1 — less than a cheap display manages in a dark room. Everything a printed picture does in the shadows is done inside that range, and the two ways of fitting a picture into it destroy different things.

applied · Delivery One instrument, one uncertainty, six places on the scale. What an absolute uncertainty of 0.001 in measured reflectance is worth in lightness, at six levels from a four-colour solid to the paper. Nothing about the instrument changes between the rows: what changes is the slope of the lightness function, which is a straight line of 903 units per unit of luminance factor below a luminance of 0.0089 and a cube root above it. At the solid the uncertainty is 0.903 lightness units and at the paper 0.043 — 21 times as much, for the same measurement.

The scale hangs from one measurement

Black point compensation is a straight line between two blacks, and the destination's is a measurement of one patch at the darkest place a spectrophotometer is ever asked to read. The lightness scale's slope is 903 units per unit of luminance factor there and 43 at the paper, so a thousandth of a reflectance is worth nine tenths of a lightness unit at the black and four hundredths at the white. That one number moves a mid grey by nearly a quarter of a delivery tolerance, and no specification names it.

applied · Delivery

Named alongside it

The objects these essays reach for when they reach for this one.

Dynamic rangeLightnessQuality controlSpecificationClippingColour managementGamutHalftoneThe ICC profileInk limitInter-instrument agreementMeasurement uncertainty

All concepts