Colour Difference Formulae Questions and Answers

Answer: A

Correct answer: in the CIELAB space using its a and b coordinates

The subscript names the space, distinguishing the CIELAB difference from the CIELUV one written with the subscript uv. Both were published in 1976 and both are Euclidean distances, but in different spaces, so the same pair gives different numbers and the subscript is not decoration.

Answer: B

Reporting the components as well as the total shows the direction of the error. A correction can then be aimed at the right attribute. A total alone gives no direction for correction. Components tell the colourist what to change.

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 total of 1.2 says only that the batch is off; the components say whether it is too dark, too weak or the wrong hue, and each of those points to a different correction. A colourist can act on the components and can do very little with the total alone.

Answer: D

Correct answer: hue angle differences do not translate simply into distances

A given change in hue angle corresponds to a small displacement near the neutral axis and a large one out at high chroma, so the angle alone does not measure how different the colours look. \( \Delta H^* \) is therefore computed as the remainder after lightness and chroma are accounted for, which gives it the units and the scale of a distance.

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. Arc length is the angle times the radius, and chroma is the radius in this space, so five degrees of hue at a chroma of 60 is a far larger displacement than five degrees at a chroma of 10. This is why hue tolerances are expressed as \( \Delta H^* \) rather than in degrees.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: \( \Delta H^* \) has the units of a distance and is obtained from the total difference after the lightness and chroma components are removed. Statement 3 is precisely what it is not - equating it to the angle in degrees would ignore the chroma at which that angle is subtended.

Answer: C

Tolerances that are correct in one region of the space prove wrong in another. Weighted formulae were developed specifically to correct this behaviour. Tolerance varies greatly across the space. One figure cannot serve everywhere at once.

Answer: D

Both are true and the reason gives the cause, and dark saturated colours tolerate more. A single figure is therefore either too tight in some regions or too loose in others. Dark saturated colours tolerate more difference.

Answer: A

It was created for the textile industry and became widely used there. Its weighting functions treat lightness, chroma and hue separately. It was developed for textile applications. Textile data was what it was fitted on.

Answer: B

Correct answer: the relative weighting given to lightness against chroma

CMC is written CMC(l:c), and the ratio sets how much a lightness difference is discounted relative to a chroma difference. The textile convention is 2:1, which reflects the trade’s greater tolerance of a shade being slightly light or dark than of it being off in chroma; 1:1 is used for perceptibility work.