Visual Imaging and the Electronic Age Fundamentals of Human Perception Lecture #20 November 7, 2017 Prof. Donald P. Greenberg
Visual Imaging and the Electronic Age
Fundamentals of Human Perception
Lecture #20November 7, 2017
Prof. Donald P. Greenberg
Review
Fundamentals of Human Perception• Retina, Rods & Cones, Physiology• Receptive Fields• Field of View• Visual Acuity of Resolution• Opponent Color Theory• Compression• Bandwidth Limitations• Saccades
Cross Section of Eye & Retina
Rods & Cones
Comparison of a rod cell (right) and cone cell (left). This shows how each cell acquired its name from its shape.
http://www.chemsoc.org/exemplarchem/entries/2002/upton/cones.htm
Adapted from Levine, Vision in Man and Machine © McGraw-Hill, 1985.
Light goes in this direction
Photoreceptors
• 120 million rods• 7-8 million cones
in each eye
Rods and Cones
Receptor Distribution
Retina Statistics
Receptive Fields –
Individual cone signals can either add together or be subtracted from one another.
The ability to resolve fine details depends ultimately on both the spatial mosaic of the receptors and how they interconnect.
Fundamentals of Human Perception• Retina, Rods & Cones, Physiology• Receptive Fields• Field of View• Visual Acuity of Resolution• Opponent Color Theory• Compression• Bandwidth Limitations• Saccades
Receptive Fields
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Receptive Fields
http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_10_39_labeled.jpg
Rods and Cones
Receptive Fields
S. Deleniv. The Neurosphere. 2016.
Fundamentals of Human Perception• Retina, Rods & Cones, Physiology• Receptive Fields• Field of View• Visual Acuity of Resolution• Opponent Color Theory• Compression• Bandwidth Limitations• Saccades
Field of view
Wikipedia
Field of View
“Foundations of Sensation and Perception.” Mather, George. 2009.
Field of View for Humans• Humans have an almost 180 degree frontal horizontal
field of view
• The vertical range of the visual field is approximately 135 degrees
• The resolution, color discrimination, and reaction times is not uniform across the field of view
Fundamentals of Human Perception• Retina, Rods & Cones, Physiology• Receptive Fields• Field of View• Visual Acuity of Resolution• Opponent Color Theory• Compression• Bandwidth Limitations• Saccades
Upper figure adapted from Cornsweet. Visual Perception © Academic Press, 1971.
Two rightmost figures from Graham, Vision and Visual Perception © Wiley, 1966.
vernier5-7”
min. detectable0.5”
min. resolvable30”
Snellen letters30”
detection resolution localization
Measures of Acuity
luminance profiles
resolution targets
resolvable unresolvable
Resolution Limits
• resolution is a function of contrast sensitivity
Resolution Limits
a
x/arc-minute
θ
a = distance from the screen
θ = angle measured in arc-minutes
Resolution Limit for Reading at 18"
The triangle subtended by a 30 second angle
Sine of 30 sec = sine of 1/120 deg
= sin (0.0083333333)
= 0.000145444
Thus 18"sin(30 sec)
= 0.002617994"
Visual Acuity
• Visual acuity is defined as “1/a where a is the response in arc-minutes”.• This acuity is usually measured by a grating test pattern and thus is
defined using a line pair. • It takes two pixels to generate a line pair (black and white). • Based on a large number of tests, the resolution of the human eye
is approximately 0.3 arc minutes.
How many megapixels are necessary to match the resolution of the human eye?
Visual Acuity ExampleAssume 120 degree x 90 degree field of view
120 * 90 * 60 * 60 / 0.3 * 0.3 = 432 megapixels
Fundamentals of Human Perception• Retina, Rods & Cones, Physiology• Receptive Fields• Field of View• Visual Acuity of Resolution• Opponent Color Theory• Compression• Bandwidth Limitations• Saccades
• Four particular colors appear to be “unique”.– Red, Green, Blue, and Yellow
• He considered these to be the “cardinal directions” of chromaticity
• All other colors seem to be intermediate between these four
Opponent Color Theory Hering 1892
Figure 12.1– Foundations of Sensation and Perception, George Mather
Opponent Color Theory Hering 1892
Biconical Color Solid
George Joblove
Biconical Color Solid
George Joblove
Color Addition (Red/Green Axis)(I)
YIQ http://en.wikipedia.org/wiki/YIQ
Color Addition (Yellow/Blue Axis)(Q)
YIQ http://en.wikipedia.org/wiki/YIQWikipedia
Analog Computing
Channel Combination Resolution
black - white M + L very high
Green - red M – L High
yellow - blue M + L – S low
Opponent Color Theory
Image from “Eye, Brain, and Vision,” David Hubel, 1988
There are three types of color receptive fields called opponent channels.
Black – White (luminance) channel M + L
Green – Red channel M - L
Yellow – Blue channel M + L - S
Opponent Color Theory Hering 1892
Cones interconnect in the retina, eventually leading to opponent-type signals.
Roy S. Berns. “Billmeyer and Saltzman’s Principles of Color Technology, 3rd Ed. 2000, John Wiley & Sons, Inc. p. 16.
Opponent Color Theory Analog Computing
Figure 12.9– Foundations of Sensation and Perception, George Mather
Ocular Motor Systems (OMS)• With normal visual perception, the ocular motor systems
control the movement of the eyes to focus on the object of interest (voluntarily controlled)
• The OMS produces adjustments in pupil size, lens refraction, and accommodation.
• Accommodation involves the convergence of the two eyes to direct their images on to the fovea.
Ocular Motor ControlDragoi, UTexas Med School
Vergence
• The simultaneous movement of the pupils of the eyes toward or away from one another during focusing.
• This measure of the convergence or divergence of a pair of light rays is defined as vergence.
Diagram of Vergence
Vergence Accommodation Conflict• Computer and projection displays present images
on a single surface but have a focal distance (blur on the retina) which may be in front of or behind the screen
• The inability to fuse the binocular stimuli causes discomfort and fatigue to the viewer
David M. Hoffman, Ahna R. Girschick, Kurt Akeley, Martin S. Banks. “Vergence-accommodation conflicts hinder visual performance and cause visual fatigue, Journal of Vision, vol. 8, no. 3, article 33, March 28, 2008.
Vergence – Accommodation Conflict
Extraocular Muscles
“Foundations of Sensation and Perception.” Mather, George. 2009.
Changing Lens Shape
Binocular Vision• Binocular Vision, which is the basis for stereopsis
is important for depth perception and covers 114 degrees(horizontally) of the human visual field.
• The remaining sixty to seventy degrees have no binocular vision (because only one eye can see those portions of thevisual field)
Time Dependent Responses
Time Response of Rods and Cones
“Foundations of Sensation and Perception.” Mather, George. 2009.
Time Response of Cones500 ms
Time Response of Rods
500 ms
Fundamentals of Human Perception• Retina, Rods & Cones, Physiology• Receptive Fields• Field of View• Visual Acuity of Resolution• Opponent Color Theory• Compression• Bandwidth Limitations• Saccades
The Optomotor Cycle
Saccade Control
• Saccade control is the ability of the eye(s) to move quickly from one fixation point to another (100-300 ms)
• To obtain a complete picture, normal adults perform 3-5 saccades (“snapshots”) per second
• Fixation “restops” are ≈ 50-100 ms
Peak Angular Velocity
Wikipedia
Saccadic Motion
Saccadic Motion
- David H. Hubel. EYE, BRAIN, AND VISION, 1988 Scientific American Books, Inc. p. 80.
- David H. Hubel. EYE, BRAIN, AND VISION, 1988 Scientific American Books, Inc. p. 80.
Saccadic Motion
The eye jumps, comes to rest momentarily (producing a small dot on the record), then jumps to a new locus of interest.
- David H. Hubel. EYE, BRAIN, AND VISION, 1988 Scientific American Books, Inc. p. 80.
Saccadic Motion
Saccadic Masking
• Visual saccadic suppression• The brain selectively blocks visual processing during eye
movements• Neither the motion of the eye or subsequent motion blur of the
image nor the time gap in visual perception is noticeable to the viewer
Saccadic Masking
• There are two major types of saccadic masking or suppression• Flash suppression is the inability of the light to see a flash of light
during a saccade• Suppression of image displacement is characterized by the
inability to perceive whether a target has moved during a saccade.
End