3 - LIGHTNESS CONSTANCY

Question 1

lightness

Answer 1

‘achromatic version of shade’

‘corresponds to differences in how dark or light a grey thing looks’

lightest possible = white
darkest possible = black

must be achromatic to be called lightness

• can have chromatic shades but ‘there is no single dimension of lightness-darkness that describes these’

Question 2

how are there different shades of colours

Answer 2

‘there are different shades of all colours and different shades are a given colour are due to subtle differences in the shape of the reflectance functions of surfaces of that colour’

• shade can sometimes be influenced by the spectrum of illumination as colour constancy is not always always achieved

Question 3

lightness (shades of grey)

Answer 3

correspond to the height of reflectance functions rather than the shape of them

• eg how reflective the surface is across the visible range
• reflect less than 5% = black

Question 4

lightness constancy

Answer 4

‘the shade that something appears does not change when the intensity of the illumination changes’

eg a piece of paper looks white regardless of the light shone on it

so lightness is not determined by how much light is reaching the eye, it is how the information about the reflectance in the visible range is presented in conscious experience

‘the achromatic version of colour constancy’ is that grey doesn’t change shade depending on the intensity of illumination