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Study Guide #4 -- Fall 20131) What is “projective geometry”? Explain how foreshortening and size scaling help us interpret scenes in 3 dimensions.a. Projective Geometry: the geometry that describes the transformations that occur when the three-dimensional world is projected onto a two dimensional surface. It investigates themathematical relationships between objects in the environment and their optical projections on the retina or a picture. b. Foreshortening: The changes in surface orientation cause projected shapes to change. It helps us interpret 3D by the use of perspective to represent in art the apparent visual contraction of an object that extends back in space at an angle to the perpendicular plane of sigh. c. Size scaling: changes is surface depth cause projected size to change2) What are the 4 perceptual biases the visual system relies on to resolve ambiguities in mapping 2-D visual information into 3-D perception. Give an explicit example of each.a. Unless there is information to the contrary, objects will be perceived as resting on the ground. Example: Information fromshadows or indirect illumination can override the bias to perceive objects to be in contact with the ground. b. There is a strong bias to interpret scenes such that depth increases with height in the viewing plane. Example: c. Convex interpretations are preferred over concave ones. Example: Circles with shadow on bottom – convex d. Interpretations involving generic views are preferred over those that require a specific vantage point. Example: Rock sculpture in Blackhawk, CO. 3) What is an Ames Room and what is the underlying principle that causes the objects within it to have illusory sizes?a. A trapezoidal room that creates an optical illusion with one large and one small person. Specially designed room that is trapezoidal in shape but appears to be rectangular from a viewpoint. This room gives misleading visual cues that leadpeople to believe that two similar-sized objects are of differentsized, depending on their location in the room. 4) What are “generic views”? Accidental views? Non-accidental properties? What relevance do they have in the study of 3D structure? Give a specific example.a. Generic views: Stipulates that the interpretation made by an observer of a distal phenomenon should be such as to not require that the observer be in a special position to, orrelationship with, the phenomenon in questionb. Accidental views: If you look straight on at a box, you see a square. If you look at a bottle, you see a circle. There are 26 combinations of ways you can define objects. Require a specific vantage point. c. Non-accidental properties: properties of an images such a co-linearity, co-termination, or parallelism that seldom occur by accident within optical projections. Thus is lines in an image are parallel (or co-terminate), they will be interpreted perceptually as if they are parallel (or co-terminating) in the 3Denvironment. Example: Parallel lines and vertices, implicit knowledge of environment regularities facilitates viewpoint invariant recognition.5) What was Brunelleschi’s Panel? What is the depth cue on which it was based?a. Brunelleschi’s Panel is a two-panel painting illustrating geometric optical linear perspective. b. Brunelleschi painted a picture of a baptistery on silver, He drilled a hole into the painting and help up a mirror and the Italians couldn’t tell the difference between the real and painted building through the pinhole. c. Depth cue: he exploited linear perspective – the idea being there is a vanishing point where al the parallel lines meet up 6) What is anamorphic art? Give three examplesa. Distorted projection or perspective requiring the viewer to use special devices or occupy a specific vantage point to reconstruct the image. Anamorphosis means to form again. b. Three examples are: Julian Beever – English chalk artist, Orosz – mirror cylinder on top of finger painting, Varlini- yellow square on picture (continuous contours), Cinemaschope,Panavision, technirama7) How, in principle, could the visual system use ocular-motor cues to deduce the relative distances of objects from the viewer?a. Visual systems in principle could use ocular-motor cues to deduce the relative distances of objects from the viewer by convergence and accommodationb. There are cues based on the ability to sense the position of oureyes and the tension in the eye muscles. 8) What is linear perspective and how can the visual system use this cueto deduce relative depth from the observer. What is the horizon ratio?a. Linear perspective is a depth cue based on the fact that lines that are parallel in the three dimensional world will appear to converge in a two dimensional image -- a type of perspective used by artists in which the relative size, shape, and position ofobjects are determined by drawn or imagined lines converging at a point on the horizon.) -- Convergence on a vanishing point.b. Horizon ratio: All objects of the same height, whatever their distance from the observer, have 1/3 above the horizon and 2/3 below. If the position on the horizon is the same then we perceive objects as the same size. – principle states that if a person is standing on flat terrain, the place where the horizon intersects the object will be one eye-height above the ground. 9) How do special effects editors create the perception of giant or diminutive people in moviesa. Forced perspective: employs the optical illusion to make an object appear on a different scale. b. Manipulates human visual perception through the use of scaled objects and the correlation between them and the vantage point of the camera.c. Displacement of objects for one to be closer to the camera andtherefore look bigger. 10) What is meant by surface texture and how can it be used to define 3-D structure? a. Surface texture is the local deviations of surface from a perfectly flat plane. The measure of the surface texture isgenerally determined in terms of its roughness, waviness, and form. 11) What is chiaroscuro? What is bas-relief a. Chiaroscuro: (light/dark) renaissance shading: shading with orientation of surface to light source, not viewer. Consistent lighting direction. Use of light to unify the scene and give 3D appearance to object – creates emotional effect. Usually the use of strong contrasts between light and dark, usually bold contrasts affecting a whole composition.b. Bas-relief: a type of sculpture in which


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OSU PSYCH 3310 - Study Guide

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