Overview

Use of colour

Why measure and specify colour?

Colour needs to be correctly communicated.
We need to talk about absolute values. To recreate exactly a colour requires an absolute definition.
Humans have a visual response to light.
Light can split up according to the wave properties.
(7:05) demo: split light into rainbow colours
8:01 “our response to that spectrum varies we don’t see all colours evenly”
- We cannot see anything in the infrared spectrum because the amount of energy is not enough to excite the photochemistry in our retina. — We are blind to infrared.
- We cannot see ultraviolet. There is a filter at the front of our eye that filter out UV.
- ‘You need less watts of green light energy to excite sensation of brightness.’ (9:00)
9:23 green and red card experiment at different brightness

Spectral reflectance is a property of material
How much light (reflectance %) that an item is reflecting as a function of wavelength?

Chlorophyll in a leaf absorb all wavelengths except green. We just see the light that the leaf doesn’t need.
18:00 illusion - see the opposite of that colour
Every colour has its opposite colour.

21:50 Colour is a three dimensional perception.
22:00 Experiment: How we perceive colour
- 1920 — (1) Take a part of visual spectrum, eg Cyan. (2) Then ask observers to adjust 3 knobs (R, G, B) to match that colour. The settings will vary by person/by eye.
- 1931 — CIE XYZ standard observer colour matching function and CIE colour space
28:22 We don’t see light linearly. Equal steps of increase in light don’t appear to us as equal increases in light as perceived.
29:50 The way we see colour varies with light level.
34:41 What you know is actually influencing what you’re seeing. (eg Banana is always yellow.)