1.2.3 Colourbased

all colours from wholly positive
mixtures of colours.
As well as the uncertainty discussed above as to how colour
perception works even in the simple cases, there are many
interesting effects that can be generated by certain kinds of stimuli.
7
CC227 Creative Computing II Perception and Information Retrieval
In this section we will look at some illusions, where the perception
of colour does not correspond to what is really there.
PatternInduced
Flicker Colours and Benham’s Top
Figure 1.2: A simplified version of the design on Benham’s top. When
spun, colours are usually perceived, but different colours are seen by
different people.
One such is Benham’s6 top, which was marketed as a toy in Victorian 6Charles Edwin Benham
(1860–1929), English amateur
scientist and polymath.
England. The basic design has half of a circle completely black, and
the other half has circular arcs; a simplified version is shown in
figure 1.2. When this disk is spun (at a rate of about 3 to 5
revolutions per second), people perceive colours from the circles
described by the arcs, usually pale reds and blues; the colours
usually change places if the disk is spun in the opposite direction.
These perceived colours are known as BenhamFechner
colours (after
those who documented them) or PatternInduced
Flicker Colours
(PIFCs).