imaging science fundamentalschester f. carlson center for imaging science the human visual system...
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Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
The Human Visual SystemThe Human Visual SystemPart 2: Perception
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Visual PerceptionVisual Perception
How one visually interprets a scene
4 forms of perception to be studied: Depth Color Temporal Motion
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
How does one determine how far away an object is located?
Depth PerceptionDepth Perception
HOW FAR ?
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Depth PerceptionDepth Perception
Monocular Cues Require only 1 eye to perceive depth;
Cyclops.
http://www.shag-art.com/cyclops.html
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Depth PerceptionDepth Perception
Binocular Cues Require 2 eyes to perceive depth.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #1Monocular Cue #1
Interposition (Overlap) An object that is
partially covered by another object is farther away.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #2Monocular Cue #2
Familiar Size Previous knowledge of
object sizes aid in judging distance.
Which object appears closer?Which object appears closer?
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #3Monocular Cue #3
Linear Perspective The farther away
an object is the smaller it appears to be.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #4Monocular Cue #4
Atmospheric Perspective Objects farther off in
the distance appear less saturated and less sharp (fuzzier) than those nearby.
The more atmospheric particles between the viewer and a distant object the more light that is scattered.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #5Monocular Cue #5
Motion Parallax Stationary objects
that are physically closer to a moving viewer appear to shift faster than those farther away.
Example 1 Driving by in a car
looking at objects near and far (animation).
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #5Monocular Cue #5
Example 2 Close one eye. Hold your left thumb
upward at arm’s length. Hold your right thumb
upward at half arm’s length.
Position the thumbs so the right thumb blocks the left and move your head to one side.
Example 3 Close one eye. Hold both index fingers
pointing toward each other.
Circle the fingers in a bike pedaling motion.
Stop them at eye level and move them inward to make them meet forming a straight line.
Observe that the background did not move, but the thumbs appeared to move relative to each other and the background.
Try again, but this time move your head side-to-side to tell the distance between your index fingers.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #6Monocular Cue #6 Shading
Perception of light falling on an object from a certain angle gives form and depth to an object.
Shadows cast by an object aid in locating it.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #7Monocular Cue #7
Patterns Use contour lines to infer depth.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Monocular Cue #8Monocular Cue #8
Accommodation The change of shape
performed by the eye lens to focus on an object aids the brain in determining the object’s distance.
Thick lens - object is near
Thin lens - object is far
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Binocular Cue #1Binocular Cue #1
Convergence The angle between the line of sight of
each eye is larger as an object moves closer.
This works for nearby objects (with accommodation)
45° 20°
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Binocular Cue #2Binocular Cue #2
Retinal Disparity Each eye receives a
slightly different view of a scene.
The two views are used to determine the ratio of distances between nearby objects.
Example Close one eye and
position your thumbs so that one blocks the other with ~1 cm distance between them.
Switch your viewing eye. Open both eyes.
Threading a needle utilizes retinal disparity.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Color PerceptionColor Perception
Trichromats Humans have three cones that correspond to
three ranges of the visible light in the areas of red, green, and blue light.
400 460 530 650600 700500
Wavelength (nm)
Rela
tive r
esp
on
se
Blue Cyan Green Red
490
I LS
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Human Color Vision DeficienciesHuman Color Vision Deficiencies
Normal Vision Viewer uses 3 basic
colors (one for each cone) to match all colors in the spectrum.
91% Males ~ 99% Females
Anomalous Trichromacy Also uses 3 basic
colors to match all colors, but the ratios of those three basic colors differ from a person with normal vision.
~ 6% Males
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Human Color Vision DeficienciesHuman Color Vision Deficiencies
Monochromacy Sensitivity to
only one color (or no color sensitivity at all)
Two types: Cone
monochromats: Only one type of cone (very small % of population)
Rod monochromats: Only the rods respond (.003% males)
Dichromacy Sensitivity to only two
colors; 8-10% of Caucasion males
Four types: Protanopes: No L cones
(1% males) Deuteranopes: No I cones
(1% males) Tritanopes: No S cones
(very small % pop.)
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Human Color Vision DeficienciesHuman Color Vision Deficiencies
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Temporal PerceptionTemporal Perception
Negative Afterimages A viewer stares at an image for a period of
time. The cones become desensitized. Upon looking at a plain white surface, the
viewer perceives the previous image with complementary colors.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Temporal PerceptionTemporal Perception
Positive Afterimages - Persistence of Vision An intense flash of light allows a viewer to
see a scene. When the light goes out the signal from the
cones persist. The viewer still perceives the image.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Motion PerceptionMotion Perception
Real Movement An object
physically moves.
Induced Movement The background
moves behind an object causing the perception that the object moved.
Imaging Science Fundamentals Chester F. Carlson Center for Imaging Science
Motion PerceptionMotion Perception
Stroboscopic Movement Quick, sequential
flashes of light / images that imply motion.
e.g. television, film, monitor
Autokinetic Movement A still spot of light
appears to move in an unlit background.
e.g. star in the night sky