Colour Science and Measurement Questions and Answers

Answer: A

Correct answer: a perception arising in the observer rather than a property of an object

Colour requires three things at once: a light source, an object that modifies the light, and an observer to receive it. What the object possesses is a spectral reflectance curve, a physical property; what the observer experiences is colour. Remove any one of the three and there is no colour, which is why the same object can look different under different lights or to different people.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct and are the two halves of the standard account: reflectance is a physical property of the surface, and colour is the perception that arises when light, object and observer come together. Statement 3 places colour in the object alone, which cannot be right - the object’s reflectance does not change when the illuminant does, but the colour seen certainly does.

Answer: C

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

Both are true and the reason is the whole of the explanation. Since colour depends on the illuminant and the observer as well as the object, changing either changes the perception while the object is untouched. This is why a fabric chosen in a shop can look quite different in daylight, and why the illuminant must be stated with any colour specification.

Answer: D

Correct answer: A-2, B-4, C-1, D-3

Four elements with four distinct roles. The source supplies the spectral power distribution. The object modifies it by reflection or transmission according to its own reflectance. The eye and brain receive what remains and form the perception. And colour is that perception - the outcome of the process rather than one of its ingredients.

Answer: A

Correct answer: 380 to 780 nanometres

The visible band runs from about 380 nm at the violet end to about 780 nm at the red, with the exact limits depending on how much sensitivity is deemed sufficient. Below it lies the ultraviolet and above it the infrared, and it is a very narrow window in the electromagnetic spectrum - less than one octave in frequency.

Answer: B

These are the hues a normal observer reports for narrow band light. The mapping is a property of the visual system rather than of the light itself. Wavelength and hue are not the same thing. One is physical and the other perceptual.

Answer: C

Magenta and purple are the familiar examples, requiring both long and short wavelengths together. They occupy the straight line closing the chromaticity diagram between the spectral extremes. The purple line closes the horseshoe shape.

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 cause. A rainbow displays the spectrum, one wavelength at each position, and magenta cannot be produced by any single wavelength - it requires long and short wavelengths together with the middle absent. Magenta is therefore non-spectral, and so are the purples generally, which is why the chromaticity diagram is closed by a straight line rather than a curve.

Answer: A

Correct answer: False

The spectral colours are only the boundary of what can be seen. The purples and magentas are non-spectral, requiring red and blue together; and every unsaturated colour - pink, brown, olive, grey - is a mixture with no single wavelength of its own. Brown in particular corresponds to no spectral line at all, being a dark orange judged against a brighter surround.

Answer: B

Colour arises from several quite different physical mechanisms. Structural colours from interference and diffraction shift with the viewing angle in a way absorption colours do not. Geometry governs one and chemistry the other.