Colour sensation - Chapter 5

What is colour

colour is a psychological representation of a mixture of lights in different wavelengths

What are the two models of colour mixing

• WHAT

• WHAT

What are the two models of colour mixing

• Additive colour mixing

• Subtractive colour mixing

Additive colour mixing

• Additive colour system starts without light (black)

• Light sources of various wavelengths combine to make colour

Subtractive colour mixing

• Subtractive colour system starts with light (white)

• Coloured inks, paints or filters between the viewer and the light source or reflective surface subtract wavelengths from the light giving it colour

• Additive = WHAT

• Adding light so light gets WHAT

• Additive = MXING LIGHT

• Adding light so light gets LIGHTER

• Subtractive = WHAT

• Subtracting light so light gets WHAT

• Subtractive = MIXING PIGMNETS

• Subtracting light so light gets DARKER

Blue light gets absorbed by a filter that is WHAT in colour

Blue light gets absorbed by a filter that is YELLOW in colour

Red light gets absorbed by a filter that is WHAT in colour

Red light gets absorbed by a filter that is CYAN in colour

Green light gets absorbed by a filter that is WHAT in colour

Green light gets absorbed by a filter that is MAGENTA in colour

Mixing green and red will produce HWTA. WHAT light comes out of a filter that is WHAT in colour

Mixing green and red will produce YELLOW. YELLOW light comes out of a filter that is YELLOW in colour

A colour absorbs its WHAT colour:

• Yellow absorbs HWTA

• Magenta absorbs WHAT

• Cyan absorbs WHAT

A colour absorbs its COMPLEMENTARY colour:

• Yellow absorbs BLUE

• Magenta absorbs GREEN

• Cyan absorbs RED

Additive and subtractive colour mixing work in WHAT directions

Additive and subtractive colour mixing work in OPPOSITE directions

Desaturating a hue (mixing one hue with another)

• In additive color mixing, when a hue is desaturated (e.g., mixing blue light with yellow light), the resulting hue is closer to WHAT.

• The opposite is true for subtractive color mixing, desaturating a hue (e.g., mixing a blue pigment with a yellow pigment) will make the resulting hue closer to WHAT

Desaturating a hue (mixing one hue with another)

• In additive color mixing, when a hue is desaturated (e.g., mixing blue light with yellow light), the resulting hue is closer to WHITE.

• The opposite is true for subtractive color mixing, desaturating a hue (e.g., mixing a blue pigment with a yellow pigment) will make the resulting hue closer to BLACK

Decreasing the value of a hue (making a hue less concentrated)

• Decreasing the value of WHAT (i.e., making it dimmer) will make the hue darker.

• Decreasing the value of a WHAT (i.e., diluting it with water or adding white to it) will make the hue brighter.

Decreasing the value of a hue (making a hue less concentrated)

• Decreasing the value of LIGHT (i.e., making it dimmer) will make the hue darker.

• Decreasing the value of a PIGMENT (i.e., diluting it with water or adding white to it) will make the hue brighter.

What are the two theories of colour vision

• WHAT

• WHAT

What are the two theories of colour vision

• Trichromatic theory

• Opponent process theory

Trichromatic theory

• Human eye has three types of WHAT with differing WHAT to different light wavelengths.

• Light of different wavelengths stimulates the three different types of WHAT in different ways.

• The WHAT of the activity of these three receptor types creates our impression of different WHAT

Trichromatic theory

• Human eye has three types of RECEPTORS with differing SENSITIVITIES to different light wavelengths.

• Light of different wavelengths stimulates the three different types of CONE RECEPTORS in different ways.

• The RATIO of the activity of these three receptor types creates our impression of different COLOURS

Opponent process theory

• Color perception depends on receptors that make WHAT responses to three pairs of colors.

Opponent process theory

• Color perception depends on receptors that make ANTAGONISTIC responses to three pairs of colors.

Trichromatic theory example:

• Light at 500 nm excites blue receptors to about 20% of their maximum, red receptor to about 55%, green receptor to about 75%. The overall color that a human sees would be like adding 20 units of pure blue light, 55 units of pure red light, and 75 units of pure green light.

A colour-blind individual is one who is born with only one or two WHAT

A colour-blind individual is one who is born with only one or two CONE RECEPTORS

The colour that the person is unable to create depend in which WHAT is missing

The colour that the person is unable to create depend in which RECEPTOR TYPE is missing

The most common deficiency is WHAT or WHAT receptor

The most common deficiency is RED or GREEN receptor

If a person is missing two types of receptors the person cannot create WHAT

If a person is missing two types of receptors the person cannot create ANY COLOURS

One weakness of the trichromatic theory is that it fails to explain
WHAT

One weakness of the trichromatic theory is that it fails to explain
COMPLEMENTARY AFTERIMAGE

Complementary colours

Colours on the opposite sides of a colour wheel.

When staring at certain colours, when you look away you will see there WHAT colour. This is called WHAT

When staring at certain colours, when you look away you will see there COMPLEMENTARY colour. This is called NEGATIVE AFTERIMAGE

The waterfall illusion, also known as the WHAT (MAE), occurs when you observe a moving stimulus for some time—like flowing water—and then look at a stationary object. The stationary object appears to drift in the WHAT direction of the original motion.

The waterfall illusion, also known as the MOTION AFTEREFFECT (MAE), occurs when you observe a moving stimulus for some time—like flowing water—and then look at a stationary object. The stationary object appears to drift in the OPPOSITE direction of the original motion.

Opponent process theory

• A stimulus triggers an WHAT reaction in one neuron but an WHAT reaction in another neuron. This process is called the WHAT process

Opponent process theory

• A stimulus triggers an EXCITATORY reaction in one neuron but an INHIBITORY reaction in another neuron. This process is called the OPPONENT process

Opponent process theory

• After repeated exposure to the same stimulus, both the WHAT and WHAT reactions WHAT

Opponent process theory

• After repeated exposure to the same stimulus, both the EXCITATORY and INHIBITORY reactions WEAKEN

Opponent process theory

• When the stimulus is removed, the WHAT neuron is released from the WHAT and becomes more WHAT than its baseline.

Opponent process theory

• When the stimulus is removed, the INHIBITED neuron is released from the INHIBITION and becomes more ACTIVE than its baseline.

Opponent process theory

• A competing theory of colour vision which assumes that the WHAT system treats pairs of colours as WHAT or WHAT

Opponent process theory

• A competing theory of colour vision which assumes that the VISUAL system treats pairs of colours as OPPOSING or ANTAGONIST

Opponent process cells are inhabited by a colour and have a burst of WHAT when its removed

Opponent process cells are inhabited by a colour and have a burst of ACTIVITY when its removed