Visual scene analysis

Question 1

How do we perceive depth? 2 types

Answer 1

1. Monocular cues (work with one eye)

2. binocular cues (require both eyes)

Question 2

monocular cues

Answer 2

• relative height and size
• occlusion
• linear perspective
• texture gradient
• motion parallax
• shadows and shading

Question 3

binocular cues

Answer 3

disparity

Question 4

relative height and size

Answer 4

• objects below horizon and have bases higher are more distant
• 2 objects of same size the more distant one will take up less of your field of view
• we need prior knowledge about sizes when judging

Question 5

occlusion

Answer 5

when objects overlap one another

Question 6

linear perspective and texture gradient

Answer 6

• parallel lines extending away from observer converge in the distance
• texture elements get smaller and more dense with distance
• foreshortening (circles become ovals) occurs when surface is tilted away

Question 7

motion parallax

Answer 7

• as we move, more distant objects will glide 0ast us more slowly than nearer objects

Question 8

shadows and shading

Answer 8

• shadows create a strong perception of depth

Question 9

Binocular disparity (Stereoscopic vision, Disparity, Horopter)

Answer 9

Stereoscopic vision
- our 2 eyes receive a slightly different image of the world

Disparity

• this creates differences in image location of an object seen by left and right eyes
• the size of the disparity depends on and objects depth

Horopter

• set of points in space that project to corresponding positions in the 2 retinas
• includes the fixation point
• Objects closer than the horopter have crossed disparities
• objects further than the horopter have uncrossed disparities

Question 10

how do we perceive objects - Structuralism

Answer 10

Wilhelm Wundt mid to late 19th century

- treated perception like periodic table where atoms evoke memories of other atoms that have been associated in memory

Question 11

how do we perceive objects - The Gestalt school

Answer 11

Wertheimer, Kohler and Koffka

- The whole is greater than the sum of its parts

Question 12

Illusory contours

Answer 12

• some images evoke the perception of edges in locations where there is no change in luminance or colour

Question 13

the gestalt principles of perceptual organisation (6 things)

Answer 13

number of principles by which elements in an image are grouped to create larger objects:

1. Proximity - things that are closer group together
2. Similarity - things that are similar group together
3. Common fate - things that move together
4. Good continuation - elements form smoothly continuing lines rather than abrupt or sharp angles
5. Closure - elements form complete figures even if incomplete
6. Symmetry - elements more likely to be formed into groups balanced by symmetry

Question 14

assessment of Gestalt principles

Answer 14

• seem correct
• however, some principles seem rather vague and imprecise (not clear on ‘good’ or ‘simple’ shape)
• no empircle evidence