This document provides an introduction to the field of computer vision. It discusses (1) the goals of understanding and modeling visual processing in humans and building artificial vision systems, (2) how the human retina represents images and the brain processes them to recognize faces and objects, and (3) psychophysical experiments used to test hypotheses about visual processing, including inattentional blindness and change blindness. Figure-ground segregation is also introduced, where only one side of a contour is perceived as the figure based on cues like symmetry, convexity, and region.
An evaluation of two popular segmentation algorithms, the mean shift-based segmentation algorithm and a graph-based segmentation scheme. We also consider a hybrid method which combines the other two methods.
An evaluation of two popular segmentation algorithms, the mean shift-based segmentation algorithm and a graph-based segmentation scheme. We also consider a hybrid method which combines the other two methods.
Understanding Human Player: Attention, Perception and Motivation / Sergei Sav...DevGAMM Conference
Over the last thirty years we have seen significant advances in computer hardware we use to develop and play games. We are now able to simulate complex physics and light matter interactions, display believable animated characters as well as provide players with expansive worlds used as settings for designer stories and playgrounds for player own stories. All of that comes at a significant cost expressed in expanding team sizes, ballooning game budgets and lengthening production timelines. To stay competitive teams feel the pressure to focus on finer and finer details in game design, art and engineering. Would these effort pay off though? Will players pay attention, perceive and be motivated enough to continue playing? These are the questions we need to often ask ourselves since human players have very real limits to their attention, perception and motivation that may well make many of the investments irrelevant. To help leads and producers with the decision making this talk will discuss the following topics: - Limits of human working memory - Interactions of visuospatial sketchpad and phonological loop - Inattention blindness - Types of human memory and memory degradation - Perception of time passage - Overview of human visual system - Central vs. peripheral vision - Perception of shapes and shadows - Perception of illumination - Perception of movement - Frame rate and human visual system - Theories of human motivation - Mostly intrinsic vs. mostly extrinsic motivation factors - Cultural differences and Hofstede dimensions Current research on these topics will be reviewed and practical notes given on how to avoid common pitfalls as well as how to identify what is likely important and what is likely less so.
1. Introduction
to
Computer Vision
ashishkhare@jkinstitute.org
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24. goals of field of vision
• understand how animals represent and
process information carried by light, by
– measuring and modeling visual performance
in humans and other animals
– finding ways to build artificial visual systems
– characterizing neural mechanisms that
• implement visual systems
– apply this understanding to obtain medical,
technological advances
25. processing of images in humans
• as a first approximation, rods and cones
(sensory cells in the retina) represent image as
large 2D array of light intensities
– about 126 million sensory cells!
• this image representation is processed by brain
enabling complex cognitive functions
– recognize a familiar face or scene
– disambiguate overlapping objects
– read sloppy handwriting
• how does the brain do all of this? how might
image processing be partitioned into subtasks?
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27. image processing tasks of brain
• possible tasks:
– extraction of contour (e.g. sharp light intensity
changes in the image)
– extraction of motion
– identification of object parts
• still unclear: how are these integrated to
enable us to extract meaning from what
we see?
30. Inattentional Blindness
Mack & Rock (1998)
• Definition: the failure to see consciously, caused by
lack of attention
• We can miss perceiving very obvious changes if we
are not attending. Subjects do not consciously
perceive features of the visual scene that they do
not attend to.
• Subjects were engaged in tasks that demanded a
high degree of attention, such as looking at a cross
and trying to determine which arm is longer.
36. Inattentional Blindness
• 25% of subjects failed to see the square when it was
presented in the parafovea (2° from fixation).
• But 65% failed to see it when it was at fixation!
• What is missed?
– Sad or Neutral face
– A word (priming for the word is present)
• What is not missed?
– Name
– Smiling face
37. Change Blindness
• Change Blindness is the phenomena were
we fail to perceive large changes, in our
surroundings as well as in experimental
conditions.
• Change could be in existence, properties,
semantic identity and spatial layout.
• Attention is required to perceive change,
and in the absence of localized motion
signals, attention is directed by high level
of interest (Rensink et al, 1997).
38. Flicker paradigm
• Basically, alternate an
original image A with a
modified image A’, with brief
blank fields placed between
successive images
39. Change Blindness
• “Visual perception of
change in an object
occurs only when that
object is given focused
attention”
• “In the absence of
such attention, the
contents of visual
memory are simply
overwritten by
subsequent stimuli,
and so cannot be used
to make comparisons”
41. Why CB?
• Change blindness could be due to –
– Poor representation of pre- and post change
scene or
– Pre change representation gets over-written
by post change representation or
– Capacity to retrieve and compare information
is limited (Hollingworth, 2003).
• Color change detection with multi-element
displays
42. Figure-Ground Segregation
• Discovered by Edgar
Rubin (Fig.1, 1921).
• Only one side of the
contour is seen as figure.
• Has shape, appears
closer.
• Background appears
Fig.1 (Faces/vase display)
behind the figure and has
no shape.
43. Background
• Configural cues:
– symmetry
– convexity
– area ………….. Gestalt psychologists
• Lower region
• lower region of a display will be seen as figure than the upper
region. (Vecera et al. 2002)
• Top-bottom polarity
• Stimuli having wide base and narrow top were perceived as
figures than the ones which had narrow base and wide top.
• (Hulleman and Humphreys, 2004)
• Higher cognitive processes
» Object memory (Mary Peterson et al. 1991)
» Attention ( Vecera et al. 2004)
44. Motivation
• Palmer and his colleagues conducted a study in which
they used temporal frequency (flicker) and manipulated
edge synchrony with the two regions (left and right).
• They concluded from their studies that edge plays the
key role in determining figure-ground segregation. In
their study they found that the region with which the
edge synchronizes will be seen as figure irrespective of
whether the region is flickering or not.
• Wong and Weisstein (1987) demonstrated that spatial
and temporal frequencies play a major role in assigning
figural status to a region.
45. Reference Books
• Fundamentals of Digital Image Processing:
Anil K. Jain
• Digital Image Processing: Gonzalez & Woods
• The Image Processing Handbook: J.C. Russ
• Digital Image Processing: B. Jahne
• Image Processing, Analysis and Machine
Vision: M. Sonka, V. Hlavac, R. Boyle
• Computer Vision Handbook: B. Jahne
• Computer Vision: M. Brady