CIE Colour Systems Questions and Answers

Answer: A

Correct answer: a specified illuminant, background and sample separation

The formula was fitted to visual data gathered under stated conditions: D65, a mid grey background, about a thousand lux, samples touching and subtending more than four degrees, with no visible texture. Departing from them does not invalidate the formula but does mean the parametric factors should be considered.

Answer: B

The first two are correct and reflect how the formulae are constructed. The third ignores the reference conditions under which the fitting was done. Universality was never claimed for the formula. Reference conditions accompany the definition.

Answer: C

Adapting luminance, surround and background all enter the calculation. It predicts brightness and colourfulness as well as lightness and chroma. Viewing conditions enter the calculation explicitly. Surround and adapting luminance both matter.

Answer: D

Relative and absolute correlates are provided for both dimensions. CIELAB offers only the relative ones and has no absolute correlates at all. Both relative and absolute forms are provided. CIELAB offers only the relative correlates.

Answer: A

Both are true and the reason gives the necessity, and the Hunt effect is the phenomenon involved. CIELAB has no term capable of representing it. Absolute luminance affects the appearance directly. The Hunt effect is the phenomenon involved.

Answer: B

A saturated blue looks brighter than a grey of the same luminance factor. CIELAB lightness takes no account of it and consequently misleads. Saturated colours look lighter than their L star. CIELAB has no term to represent it.

Answer: C

The Helmholtz Kohlrausch effect makes the more saturated one look lighter. CIELAB lightness is a function of luminance factor alone. Chroma plays no part in the L star calculation. Luminance factor alone determines lightness.

Answer: D

The equal energy point at one third each corresponds to illuminant E instead. Illuminant A sits near 0.4476 and 0.4074 on the same diagram. Equal energy sits at one third each instead. Illuminant A lies further towards the red.

Answer: A

Equal power at every wavelength gives equal tristimulus values by construction. It sits near but not exactly at the centre of the real gamut. Equal power gives equal tristimulus values. It sits near the centre of the diagram.

Answer: B

Chromaticity says nothing about the luminance and therefore nothing about lightness. Black, grey and white all share the same chromaticity coordinates. Chromaticity is normalised for luminance. The whole neutral axis maps to one point.