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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

Full Color Image

YIQ http://en.wikipedia.org/wiki/YIQ

Luminance Image (Y)

YIQ http://en.wikipedia.org/wiki/YIQWikipedia

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

Full Color Image

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