Colour Difference Formulae Questions and Answers

Answer: C

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. A physical standard fades under light, yellows with heat, and picks up soiling and surface change from handling, so the reference itself drifts. Standards are therefore stored in the dark, issued with a date, and replaced on a schedule - and the master is measured rather than merely looked at.

Answer: D

The first two are correct and describe the trade-off. The third is not generally so, since a numerical standard avoids drift entirely and travels far more easily. Each form has its own advantages. Numerical standards do not drift with time.

Answer: A

CMC was fitted largely on textile data and performs well on textiles. Extrapolating a formula far beyond its fitting conditions is always a risk. CMC performs best on textile samples. Fitting conditions bound the reliable range.

Answer: B

Both are true and the reason gives why the older formula persists, and every stored tolerance rests on it. Re-establishing them against visual judgement would be a very large undertaking. Stored tolerances tie an industry to its formula.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 are the two real considerations: a formula fitted on textile data at moderate chroma performs best there, and an industry with years of tolerance data has a substantial cost in changing. Statement 3 ignores both - adopting a newer formula means revisiting every tolerance that was set with the old one.

Answer: D

A sphere and an ellipsoid cannot be made to coincide in general. Any conversion accepts some batches the original would have rejected and the reverse. A sphere and an ellipsoid cannot coincide. Conversion is approximate at best.

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. A tolerance of 1.0 in \( \Delta E^*_{ab} \) defines a sphere, while the same number in CMC or CIEDE2000 defines an ellipsoid oriented differently at every point in the space. Carrying the number across changes both which batches pass and which direction of error is treated most severely.

Answer: B

Correct answer: inadequate, since the formula and conditions are unstated

A difference figure means nothing without the formula, the illuminant, the observer and any parametric factors applied, because each of those changes the number. A reader given the value alone cannot compare it with another value or apply it to a specification - and the smallness of the number does not repair the omission.

Answer: C

Correct answer: the price paid for the material

What must accompany the figure is everything that would change it if changed: the formula, the illuminant and observer, and the parametric factors. Commercial terms have no effect on the calculation, however much they may bear on what tolerance is agreed.

Answer: D

The convention subtracts the standard from the batch throughout. A negative value therefore means the batch has the lower lightness. Batch minus standard is the usual convention. A reversed convention flips every sign.