Colour Vision and Observer Questions and Answers

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 give the two observers correctly. Statement 3 is precisely what is not true: they were defined for different field sizes because the retina’s composition varies, and they give different tristimulus values for the same sample - which is why quoting a colour without naming the observer leaves the figure ambiguous.

Answer: B

Its density varies between individuals and falls with distance from the fovea. It is one of the principal causes of both observer variability and the difference between the two observers. Its density varies widely between individuals.

Answer: C

The illuminant is a property of the lighting rather than of the observer. The other three are genuine sources of observer to observer variation. The illuminant belongs to the lighting instead. Only the first three are properties of the eye.

Answer: D

Correct answer: receive less short wavelength light at the retina

The lens yellows progressively through life, and a yellow filter is one that absorbs blue. The retina of an older observer therefore receives less short wavelength light, which changes colour matches slightly and degrades blue discrimination. Long wavelength transmission is barely affected.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Yellowing of the lens removes short wavelength light before it reaches the receptors, so the S cone signal is weakened and blue discrimination declines. This is a normal consequence of ageing rather than a deficiency, but it is a real source of disagreement between observers of different ages.

Answer: B

Correct answer: a pair matches for one observer but not for another

Observer metamerism is the observer analogue of illuminant metamerism: the samples differ spectrally, and two people whose colour matching functions differ slightly integrate that difference differently. It is why a match agreed by one colourist can be rejected by a colleague with entirely normal colour vision.

Answer: C

In every case a pair matches under one condition and fails under another. The underlying cause is always that the spectral curves differ while the tristimulus values agree. Any change of condition breaks the coincidence.

Answer: D

Both are true and the reason gives the cause, and changing any condition breaks the coincidence. A spectral match cannot fail under any change whatever. Identical curves match unconditionally. No change of illuminant or observer can break it.

Answer: A

Identical curves match under every illuminant and for every observer. Such a match is described as an unconditional or spectral match. Nothing can break such a match. Identical spectra are the only guarantee available.

Answer: B

Only a spectral match survives every change of illuminant and observer. Achieving one usually requires the same colourants in the same proportions. Only identical colourants give identical curves. Substitution therefore risks a metameric result.