Image Perception

Image Perception Drawing hands by M.C Escher Waterfall by M.C Escher EE465: Introduction to Digital Image Processing 1 Human Eye Structure Three membranes enclose the eye: Cornea and sclera, Choroid, Retina ciliary body Pupil size: 2-8mm iris diaphragm Eye color: melanin (pigment) in iris EE465: Introduction to Digital Image Processing 2 Retina When the eye is properly focused, light from an outside object is imaged on the retina Two classes of receptors are located over the surface of retina: cones and rods Cone: 6-7 million in each eye, central part of retina (fovea) and highly sensitive to color Rod: 75-150 million, all over the retina surface and sensitive to low levels of illumination EE465: Introduction to Digital Image Processing 3 Rods and Cones in Retina EE465: Introduction to Digital Image Processing 4 Image Formation in the Eye Focal length: 14-17mm Length of tree image2.55mm For distant objects (>3m), lens exhibits the least refractive power (flattened) For nearby objects (<1m), lens is most strongly refractive (curved) EE465: Introduction to Digital Image Processing 5 Lightness Perception: Objective Quantities  Luminance is the amount of visible light that comes to the eye from a surface.  Illuminance is the amount of light incident on a surface.  Reflectance (also called albedo) is the proportion of incident light that is reflected from a surface. varies from 0% to 100% where 0% is ideal black and 100% is ideal white. In practice, typical black paint is about 5% and typical white paint about 85%. http://www-bcs.mit.edu/people/adelson/publications/gazzan.dir/gazzan.htm EE465: Introduction to Digital Image Processing 6 Image Formation Model f(x,y)=i(x,y)r(x,y) 0