Unit 2.1 and 2.2 Trichromacy and Colour Mixing

Question 1

What kind of property is colour?

Answer 1

not a physical property but a psychophysical property

Question 2

What wavelength of light do we perceive?

Answer 2

400-700nm

Question 3

What are the steps to colour perception?

Answer 3

1. Detection: wavelengths of light must be detected in the first place
2. Discrimination: we must be able to tell the difference between one wavelength (or mixture) and another
3. Appearance: we want to assign perceived colours to lights and surfaces in the world and have those perceived colours be stable over time, regardless of different lighting conditions

Question 4

How many photoreceptors does the retina contain?

Answer 4

four (S,M,L cones and rods)

Question 5

What is scotopic?

Answer 5

it refers to dim light levels at or below the level of bright moonlight

Question 6

What kind of light are rods sensitive to?

Answer 6

scotopic light levels

Question 7

What kind of photopigment do all rods contain?

Answer 7

Rhodopsin

Question 8

Why can’t rods discriminate light?

Answer 8

all rods have the same sensitivity to wavelengths

Question 9

What is photopic?

Answer 9

light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors (rods are unless bc they can’t discriminate)
- sunlight and bright indoor lighting

Question 10

What are the cone photoreceptors?

Answer 10

S-cones(420nm): sensitive to short wavelengths (blue)
M-cones (535nm): sensitive to middle wavelengths (green)
L-cones(565nm): sensitive to long wavelengths (red)

Question 11

Which cones have the highest density?

Answer 11

L cones then S cones

Question 12

What is Trichromacy?

Answer 12

Trichromacy is the theory that the color of any light is defined in our visual system by the relationships between the outputs of three types of photoreceptors (S, M, and L cones). It explains how we perceive color through the combination of these three cone types.

Question 13

What is the Problem of Univariance?

Answer 13

The Problem of Univariance states that a single type of photoreceptor cannot distinguish between different wavelengths of light based solely on its response. An infinite set of different wavelength-intensity combinations can elicit the same response from one type of cone.

Question 14

What is the significance of the Young-Helmholtz theory?

Answer 14

The Young-Helmholtz theory (Trichromatic theory) posits that color perception is based on the output of three types of cones. It was developed from behavioral observations and later supported by physiological evidence showing the existence of three cone types.

Question 15

What did Isaac Newton discover?

Answer 15

that white light is composed of a spectrum of hues by using a prism
- and adding a second prism, recombined the hues into a white light

Question 16

What was the main purpose of James Clerk Maxwell’s color-matching experiments?

Answer 16

To investigate how different wavelengths of light can be combined to match a specific hue, thereby contributing to the understanding of color perception and the development of trichromacy theory.

Question 17

How did Maxwell conduct his color-matching experiments?

Answer 17

Maxwell used a bluish light and adjusted the intensities of three other lights (red, green, and blue) to match the bluish light, demonstrating the additive nature of color mixing.

Question 18

Why are Maxwell’s experiments important in the study of color perception?

Answer 18

They provided empirical support for the trichromatic theory of color vision, showing that any color can be produced by combining three primary colors of light in different proportions.

Question 19

What is the definition of Additive Color Mixing?

Answer 19

Additive color mixing is the process of combining different colors of light. When light A and light B are reflected from a surface to the eye, their effects add together, resulting in a new color perception.

Question 20

What are metamers in color perception?

Answer 20

Metamers are different mixtures of wavelengths that appear identical to the human eye. They demonstrate the principle of additive color mixing, as two different light combinations can produce the same cone responses.

Question 21

How do Metamers relate to the concept of additive color mixing?

Answer 21

In additive color mixing, different wavelengths of light are combined, and when the total stimulation of the M (medium) and L (long) cones is equal, the resulting color can appear identical to another mixture of wavelengths that produces the same cone responses, even if the wavelengths themselves are different.

Question 22

Can you provide an example of Metamers?

Answer 22

An example of metamers is when a specific shade of yellow can be produced by mixing red and green light in the right proportions. Even though the physical wavelengths of the red and green lights are different, the combination can stimulate the M and L cones in such a way that the brain perceives it as the same color as a pure yellow light of a specific wavelength.

Question 23

What is the importance of the total stimulation of M and L cones in relation to Metamers?

Answer 23

The total stimulation of M and L cones being equal is essential for the perception of color to be consistent across different light mixtures. This means that even if the actual wavelengths differ, the perceived color remains the same, which is the basis for understanding metamers.

Question 24

What are things to watch out for in metamers?

Answer 24

1. mixing wavelengths does not change the physical wavelengths
2. in order for a mixture of red light and green light to look perfectly like yellow, you have to add the right amount of red and green

Question 25

What is subtractive color mixing?

Answer 25

Subtractive color mixing occurs when pigments (or dyes) are combined, resulting in some wavelengths of light being absorbed, while others are reflected. The colors perceived are based on the remaining light that is not absorbed.

Question 26

How does mixing pigments A and B affect color perception?

Answer 26

When pigments A and B mix, they absorb certain wavelengths of light. The colors perceived depend on the wavelengths that are reflected by the mixture, which are the wavelengths not absorbed by either pigment.

Question 27

What is a reflectance curve?

Answer 27

A reflectance curve shows the proportion of light at different wavelengths that is reflected from a pigment. It illustrates how pigments absorb and reflect light.

Question 28

What are pigments?

Answer 28

substances that absorb light at some wavelength and reflect light at other

Question 29

What happens when yellow and blue pigments are mixed?

Answer 29

Yellow pigment reflects medium wavelengths (yellow and green) and absorbs short wavelengths (blue). Blue pigment absorbs long wavelengths (red and yellow) and reflects short wavelengths. When mixed, the result is green, as only the wavelengths that both pigments reflect contribute to the perceived color.

Question 30

How can filters demonstrate subtractive color mixing?

Answer 30

Filters can absorb specific wavelengths of light. For example, a yellow filter absorbs short wavelengths (blue) and transmits longer wavelengths (red and green), resulting in a yellowish color. When combined with a filter that absorbs long wavelengths, the resultant color can appear green.

Question 31

What is Pointillism?

Answer 31

Pointillism is a painting technique developed by Georges Seurat in which small dots of color are applied to the canvas. The technique relies on additive color mixing, where the viewer’s eye blends the colors at a distance to create a fuller range of hues.

Question 32

How does Pointillism relate to color mixing?

Answer 32

Pointillism utilizes additive color mixing, meaning that colors are created by placing dots of different colors close together. When viewed from a distance, the colors visually blend, producing vibrant and complex colors without physically mixing pigments.

Question 33

What is Dithering?

Answer 33

Dithering is a technique used in color quantization that reduces the number of colors needed in an image. It employs additive color mixing principles, similar to Pointillism, to create the illusion of more colors by arranging pixels of different colors in a pattern.

Question 34

Why is Dithering used in color printing?

Answer 34

Dithering is used in color printing to make the printing process more efficient by reducing the number of colors required. For example, an image can be reduced to just four colors while still appearing colorful and detailed through the arrangement of those colors.

Question 35

What is the difference between additive and subtractive color mixing?

Answer 35

Additive color mixing occurs when colors are created by combining light (as in Pointillism and digital displays), while subtractive color mixing occurs when pigments are mixed, absorbing certain wavelengths of light and reflecting others (as in traditional painting).