Colour Difference Formulae Questions and Answers

Answer: A

The first two are correct and describe the calculation. The third is impossible, since the index is defined relative to a reference condition. Two illuminants are required by definition. Reference and test are both necessary.

Answer: B

Correct answer: any residual difference under the reference would inflate the index

The index is meant to measure how much the match degrades between illuminants, not how good it was to begin with. If the pair does not quite match under the reference, that residual is carried into the test illuminant calculation and counted as metamerism. Correcting the pair to agree under the reference isolates the degradation.

Answer: C

It measures how much a single colour shifts when the light changes. A pair may be metameric while each of its members is also colour inconstant. One concerns a pair and the other a single sample. Both involve a change of illumination.

Answer: D

Both are true and the reason gives the distinction, and both involve a change of illuminant. Confusing them leads to the wrong diagnostic test. Both involve a change of illuminant nonetheless. The subject of the test is what differs.

Answer: A

Each answers a different question about the same measured data. Selecting the right index depends on what is actually being asked. Each index answers a different question. Choosing correctly requires knowing the question.

Answer: B

Correct answer: nothing about the difference under any other illuminant

Zero difference under one illuminant means the tristimulus values coincide there, which the samples can achieve with quite different spectral curves. Under another illuminant those curves integrate differently and the difference reappears. Only identical reflectance at every wavelength - an unconditional match - guarantees zero everywhere.

Answer: C

Correct answer: False

A match under D65 need only be a metameric match, and D65 and illuminant A differ about as much as two illuminants in practical use can - average daylight against tungsten. A pair agreeing under the first commonly fails badly under the second, which is why both are so often specified together.

Answer: D

Correct answer: the components and the direction of the difference

A total of 1.5 could mean the batch is a little dark, a little weak, or noticeably off in hue, and those call for quite different corrections. The components with their signs say which, and since hue is the least tolerated of the three, the same total is not equally serious in every direction.

Answer: A

Each step depends on the one before it and on the agreed specification. Omitting the illuminant agreement makes the whole exercise unreproducible. Agreement precedes measurement in every case. Illuminant and formula must be settled first.

Answer: B

Correct answer: a physical sample or a set of agreed numerical values

The standard must be something both parties can refer to and neither can dispute, so it is either a physical sample held by both or an agreed set of values with the measurement conditions stated. A supplier’s shade card, a previous batch or a colourist’s recollection are none of them a defined reference.