CIE Colour Systems Questions and Answers

Answer: C

Correct answer: extending a line from the white point through the sample to the locus

The construction runs outward from the white point through the sample and continues to where it meets the spectrum locus, and the wavelength at that intersection is the dominant wavelength. It gives a rough correlate of hue, and how far along the line the sample sits gives the excitation purity.

Answer: D

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. The purple line joins the two ends of the spectrum locus and corresponds to no single wavelength, since no monochromatic light is purple. A line from the white point through a purple meets that line rather than the locus, so the construction is reversed - extended backwards to the locus, giving a complementary wavelength written with a c or a minus sign.

Answer: A

It runs from zero at the white point to one on the locus itself. It is a geometric quantity on the diagram rather than a perceptual attribute. Zero at the white point and one on the locus. It is a geometric rather than perceptual measure.

Answer: B

The first two are correct and describe the pair of quantities. The third is not so, since the xy diagram is markedly non-uniform perceptually. Geometric purity is not perceived saturation. The diagram is markedly non-uniform throughout.

Answer: C

Correct answer: equal distances do not correspond to equal perceived differences

The diagram compresses the blues and greatly expands the greens, so a given separation may be plainly visible in one region and invisible in another. MacAdam demonstrated it by measuring discrimination ellipses across the diagram, and the whole development of uniform colour spaces followed from the demonstration.

Answer: D

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. Each ellipse marks the region within which colours are indistinguishable from its centre, and they vary in area by a factor of about twenty between the blue and the green - which is a direct measurement of the diagram’s non-uniformity.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: the ellipses bound the just noticeable differences and vary greatly in size across the diagram. Statement 3 states what a perceptually uniform diagram would show and what the xy diagram conspicuously does not - the ellipses are neither circles nor of equal size.

Answer: B

It is a projective transformation of the xy diagram rather than a new measurement. Uniformity is much improved but remains far from perfect. It is a projection rather than new measurement. No new experimental data was required.

Answer: C

Both are true and the reason gives the nature of the transformation, and no new data is required. Straight line mixing is preserved, which a non-projective transformation would destroy. Straight lines map to straight lines under it.

Answer: D

A projective transformation maps straight lines to straight lines. This is precisely why a projective form was chosen for the uniform diagram. Additive mixing had to remain simple. A projective form preserves straight lines.