natural vision systems ece 847: digital image processing stan birchfield clemson university
TRANSCRIPT
Natural Vision Systems
ECE 847:Digital Image Processing
Stan BirchfieldClemson University
Animal visionWhich has “the most complicated eye in the animal kingdom?”
Tropical mantis shrimp
Sees at least 11 color dimensions!• 8 pigments sensitive to visual light• 3 to ultraviolet
Also• has 4 filters to tune the pigments• sees 2 or 3 planes of polarized light
Lives at depths of 40m, where light is only filtered, dim blue. Why such complex vision?• shrimp communicate with each other by fluorescing their spots
http://www.innovations-report.de/html/berichte/biowissenschaften_chemie/bericht-23390.html
Color vision in bees
flower as seen by a bee
http://www.wonderquest.com/nectar-guides.htm
Bees have ultraviolet filters to help them see their target:
Color vision in mammalsHow does the bull see the cape?
Motion, not color!
Generally speaking, only
primates and humans (among mammals)
can see color
Visual acuity
Raptors (including eagles, hawks, and falcons) can see up to 8 times more clearly than humans
Golden eagle can see a hare a mile away!
Which animal has the sharpest vision?
http://ebiomedia.com/gall/eyes/sharp.html
Speed
fly can process images at 200 Hz
http://www.eyedesignbook.com/ch3/eyech3-c.html
Nautilus eye
What is unusual about the nautilus eye?
It has no lens!
http://www.eyedesignbook.com/ch3/eyech3-b.html
Lobster eye
What is unusual about the lobster eye (and some other crustaceans)?
It focuses light by reflection, not refraction
(design has inspired Lobster Eye telescope)
http://www.answersingenesis.org/creation/v23/i3/lobstereyes.asp
Brittlestar
Where is the brittlestar eye?Its whole body!
Brittlestar secretes calcite crystals that form microlenses
The “oldest” eye
http://www.trilobites.info/eyes.htm
Descartes’ lens design for minimal aberration
Huygens’ lens design for minimal aberration
trilobite
trilobite
trilobite eyes
An exerciseinterpolate this function:
?
?
time
maximum complexity
of animal eye
500M4B
Irreducible complexity
from M. Behe, Darwin’s Black Box
A single photovoltaic cell:
Human visual system
[from P. Gurney]
Visual pathway
Retinal cells
retinal pigment epithelium (RPE)
light
optic nerve fibers
ganglion cells
amacrine cellsbipolar cellshorizontal cells
photoreceptors
[from S. Palmer, Vision Science]
Retinal cells
http://webvision.med.utah.edu/sretina.html
Foveation
central retina: color and form perceptionperipheral retina: light detection, motion detection, night vision
only cones in foveola
Cones
http://mbb.harvard.edu/evolution_of_mind_and_brain/chapter_2.pdf
some birds, insects,and fish see ultraviolet
some snakes,insects,and batssee infrared
Macula Lutea
macula lutea –yellow pigmentation
(Xanthophyll)in foveal area
Xanthophyll in Muller cells absorbs damaging short-wavelength light (420-450 nm)
Inverted retina allows• Muller cells in fovea to protect photoreceptors• RPE, which is opaque, to nourish and protect photoreceptors
• RPE and choroid absorb 25-33 % of light entering eye• Choroid acts as heat sink (has the highest blood flow per gram of tissue of all tissues in the body)
Besides, in foveola• cones are packed tightly together and elongated• layers of retina are spread aside, permitting light to fall directly on cones• Muller cells act like optic fiber plates to transmit light to receptors
Why an inverted retina?
verted retina
(common in invertebrates)
inverted retina
(common in vertebrates)
lightlight
[P. Gurney, Is our inverted retina really bad design?, 1999]
Visual processing
Overlapping fields of view
rabbit person
Characteristics of human vision
• Vision is an interpretive process– The raw data is insufficient– Processes in the brain impose a priori
assumptions to make sense of the data– Examples: brightness, color, and size constancy
• Vision solves specific tasks in specific contexts– Visual skills directly tied to needs and context– Examples: Thatcher illusion, Chernoff faces
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html
Brightness constancyPerceived brightness is complex function of pixel values
(Image courtesy of Ted Adelson)
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html
Color Constancy
Pixel color strongly affected by illumination.
Perception of color constancy maintained by the brain
Sunlight Fluorescent light
(Images courtesy of David Heeger)
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html
Size Constancy
Object size vs. object depth
(Images copyright John H. Kranz, 1999)
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html
Thatcher Illusion
(Due to P. Thompson)
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html
Thatcher Illusion
Face processing is sensitive to orientation.
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html
Chernoff faces
Useful for displaying multivariate data
Integration of Information
• Spatial information in the image must be integrated to perceive a coherent object
Fixation experimentsYarbus 1961
Fixations for “Give theages of the people”
Fixations for “Whatwere they doingbefore the guestarrived?”
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html
Recognition of Objects
(Due to Ron Rensick)(Due to R. James)
Grouping is affected by top-down processes
Context influences recognition of parts
http://www-static.cc.gatech.edu/classes/AY2007/cs4495_fall/html/materials.html