Unit 2.5 and 2.6 Colour in The World and Monocular Depth Cues

Question 1

What is color contrast?

Answer 1

Color contrast is a color perception effect in which the color of one region induces the opponent color in a neighboring region. For example, a small red square appears redder when surrounded by green, while a green square appears greener when surrounded by red.

Question 2

How does color contrast affect perception?

Answer 2

Color contrast enhances the perceived intensity of colors by creating a visual relationship between adjacent colors, making them appear more vivid and distinct from one another.

Question 3

What is color assimilation?

Answer 3

Color assimilation is a color perception effect in which two colors bleed into each other, with each color taking on some of the chromatic quality of the other. This can create a blended appearance where the colors seem to merge.

Question 4

What is the goal of colour perception?

Answer 4

• to perceive changes in illumination (colour of light)
• to perceive changes in reflectance (colour of objects)

Question 5

What is an illuminant?

Answer 5

An illuminant is the light source that illuminates a surface, affecting how colors are perceived.

Question 6

What is color constancy?

Answer 6

Color constancy is the ability of the visual system to perceive colors of objects as relatively stable under varying lighting conditions. It allows a surface to appear the same color despite changes in illumination.

Question 7

What are some technical approaches to achieve correct color constancy?

Answer 7

1. Using surfaces with known reflectance properties (e.g., white balance).
2. Illuminating the scene with a known light source (e.g., pre-flash).
3. Computational approaches, such as inverting the illumination process or using machine learning techniques.

Question 8

Why is estimating the illuminant a problem for cameras?

Answer 8

Cameras often struggle to accurately guess the illuminant due to varying light conditions, which can lead to incorrect color representation in photographs.

Question 9

What was the primary purpose of the McCann, McKee, and Taylor experiment?

Answer 9

The primary purpose was to investigate how color perception and discrimination are influenced by the surrounding colors and the context in which colors are viewed.

Question 10

What were the key findings of the McCann, McKee, and Taylor experiment?

Answer 10

The study found that color discrimination is significantly affected by the context of surrounding colors, demonstrating the importance of color contrast and the influence of adjacent colors on perception.

Question 11

What physical constraints make constancy possible?

Answer 11

• intelligent guesses about the illuminant
• assumptions about light sources
• assumptions about surfaces

Question 12

Why do animals provide insight into colour perception?

Answer 12

For food and sex
- foraging for coloured food is easier
- advertisements for bees to trade food for sex
- colourful patterns on tropical fish and toucans provide sexual signals

Question 13

What is colour in the periphery?

Answer 13

an illusion because the density of cones falls in the periphery

Question 14

What is Euclidean geometry?

Answer 14

Euclidean geometry is a mathematical system where parallel lines remain parallel as they are extended in space, and objects maintain the same size and shape as they move around in space.

Question 15

How does Euclidean geometry relate to perception?

Answer 15

Images projected onto the retina are non-Euclidean, presenting a challenge to reconstruct a Euclidean world from this non-Euclidean stimulation.

Question 16

What are the two types of depth cues mentioned in relation to spatial perception?

Answer 16

The two types of depth cues are monocular depth cues (available with one eye) and binocular depth cues (relying on information from both eyes).

Question 17

What are monocular depth cues?

Answer 17

Monocular depth cues are depth cues that are available even when the world is viewed with one eye alone. They help in perceiving depth and distance in a two-dimensional image.

Question 18

What is the difference between nonmetrical, relative metrical, and absolute metrical depth cues?

Answer 18

• Nonmetrical depth cue: Provides information about relative depth order but not depth magnitude (e.g., which object is in front of another).
• Relative metrical depth cue: Provides quantitative information about relative depth (e.g., “object A is twice as far away as object B”).
• Absolute metrical depth cue: Provides quantitative information about absolute distance (e.g., the exact distance to an object).

Question 19

What is occlusion as a monocular depth cue?

Answer 19

Occlusion is a cue to relative depth order where one object obstructs the view of part of another object, indicating that the occluding object is closer.

Question 20

Describe aerial perspective as a monocular depth cue.

Answer 20

Aerial perspective is a depth cue based on the scattering of light by the atmosphere. More distant objects appear fainter, bluer, and less distinct due to increased light scattering.

Question 21

What is texture gradient?

Answer 21

Texture gradient is a depth cue based on the geometric fact that items of the same size form smaller images when they are farther away, providing a sense of depth based on the density of texture.

Question 22

Explain relative size as a monocular depth cue.

Answer 22

Relative size is a comparison of size between items without knowing the absolute size of either one. For example, two balls of the same size will appear different in size based on their distance from the viewer.

Question 23

What is the relative height?

Answer 23

more distant objects are higher in the visual field

Question 24

What is familiar size as a monocular depth cue?

Answer 24

Familiar size is a depth cue based on knowledge of the typical size of objects. For instance, knowing the average size of a human allows us to judge their distance based on their perceived size.

Question 25

What is motion parallax?

Answer 25

Motion parallax is a monocular depth cue based on motion. Closer objects appear to move faster across the visual field than those that are farther away when the observer is in motion.

Question 26

Define linear perspective as a pictorial depth cue.

Answer 26

Linear perspective is a depth cue that involves the convergence of parallel lines in a two-dimensional image, which creates an illusion of depth (e.g., roads or railway tracks appearing to meet at a vanishing point).

Question 27

What is a pictorial depth cue?

Answer 27

a cue to distance or depth used by artists to depict 3D depth in 2D picture

Question 28

What is a vanishing point?

Answer 28

the apparent point at which parallel lines receding in depth converge

Question 29

How do monocular depth cues help in interpreting visual scenes?

Answer 29

Monocular depth cues allow the visual system to reconstruct a three-dimensional world from two-dimensional images by providing various forms of depth information, aiding in understanding spatial relationships.

Question 30

What is anamorphosis (or anamorphic projection)

Answer 30

Use of the rules of linear perspective to create a 2D image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion