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Vision
• Vision is the ability to recognize shapes, patterns and colors and to detect and estimate motion, distance and size
• The eye has evolved independently in many animals groups such as the composite eye of insects and that of our own
• The perceptual ability of human beings are learned entirely through experience
Vision - The structure of the Eye
• The cornea for refraction• The iris for controlling the pupil
diameter to control the amount of light gathered and the depth of field
• The lens with 17 mm focal length to adjust focus for objects at different distances
• The retina (180˚ field of view) is a light-sensitive spherical surface where inverted image are formed through receptors known as rods (130 million) for black and white images) and cones (7 million for color images) www.vrmny.com/anatomy.htm
Rods and Cones
• Rods peaks at about 20˚ away from the fovea and gradually fall off in number towards the edge of the retina
• Cones contains pigments sensitive to red, green and blue and are concentrated immediately around the fovea
• The blind spot where the optic nerve leaves the eye (the blind spot) there are neither rods nor cones
Additive Primary Colors• Additive primary colors:
– Red
– Green
– Blue
• In equal portions other spectral color are produced:
– Red+Green=Yellow
– Red+Blue=Magenta
– Green+Blue=Cyan
– Red+Blue+Green=White
• In non equal portions non-spectral colors are produced
Subtractive Primary Colors• Additive subtractive colors:
– Magenta
– Cyan
– Yellow
• In equal portions other spectral color are produced:
– Magenta+Yellow=Red
– Magenta+Cyan=Blue
– Yellow+Cyan=Green
– Magenta+Cyan+Yellow=Black
• In non equal portions non-spectral colors are produced
Hue-Saturation-Intensity
• Hue is the nature of the color and can be described by the wavelength. Red = 0˚ or 360˚, green = 120˚, and blue = 240˚
• Saturation = Purity of the color. Zero is completely impure and 90˚ is completely pure
• Intensity Level, or Value is the grayscale In 8 bit radiometric resolution scheme, Zero is black and 255 is white.
Color Cube for Additive Primary Colors and H-S-I
• Color cube for Additive additive primary colors and H-S-I defines the relationship between Red-Green-Blue color space and Hue-Saturation-Intensity color space
• The H-S-I color space is defined by a cone extending from black (0,0,0) to white (255,255,255) in 8 bit radiometric resolution scheme
• The Hue is defined by an angle in which Red=0˚ or 360˚; Green=120˚; and Blue=240˚
• Saturation ranges between 0˚ for completely impure color and 90˚ for completely pure color
Color Triangle for Additive and Subtractive primary Colors
• Color triangle for additive and subtractive primary colors illustrates the relationship between Red-Green-Blue and Magenta-Cyan-Yellow
• The triangle corners are occupied by Red, Green and Blue whereas the mid-points between these corners are occupied by Magenta, cyan and Yellow
• The center of the triangle is occupied by white which resulted from the sum of equal portions of Red, Green and Blue
SIR-C/X-SAR dataScattering Mechanisms
Smooth Surface
Rough Surface
Outstanding Relief
Reflection Back- Scattering
Volume- Scattering
Double- Bounce
Penetration
Paleo-channel
SIR-C/X-SAR dataPenetration
Rough sand/bedrock
interfaceSmooth
sand/paleo-channel interface
Paleo-channel (Filled with alluvium)
Fine, well sorted dry sand
(~2 m thick)
Bedrock (Cretaceous sandstone or
Neoproterozoic crystalline basement)
Reflected signal from the
air/sand interface
Back-scattered signal from the sand/bedrock
interface
Complete signal
attenuation
Refracted and Wavelength-reduced
signal through the air/sand interface
Reflectedsignal fromthe sand/
paleo-channelfill interface
Present land above 500 m
PostulatedTrans-African Drainage
LakeMega- Chad 800 km
Present drainage
Modified after Burke & Wells (1989)
Nile
Niger
Zaire
Did the Drainage of NE Africa once flow to the Atlantic?
~ Oligocene (30 Ma)