Elements of Visual PerceptionDigital Image Processing is built on foundation of Mathematical and Probabilistic formulations Human Intuition & analysis plays a key role in choosing ne technique over other. Study of Human vision system is thus important.
Image sensing and AcqusitionSimple Image formation model:o Images are denoted by 2-dimensional function of the form f( x, y).o f at spatial co-ordinates ( x, y) is positive, finite scalar quantity determinedby source of the image. 0 < f( x, y) < ∞o f( x, y) is characterized by two components: o illumination: amount of source illumination incident on scene. denoted by i( x, y) o reflectance : amount of illumination reflected by the objects in scene. denoted by r( x, y) Thus, f(x,y) = i(x,y) r(x,y) where, 0 < i(x,y) < ∞ …………….(1) & 0(total absorption)< r( x, y) < 1(total reflectance) …………….(2)
Image sensing and AcqusitionSimple Image formation model:o Let the gray level (intensity) of a monochromatic image at any co-ordinate be denoted by: l = f(x0, y0); From equation (1) & (2) we get Lmin ≤ l ≤ Lmax where, Lmin should be positive & Lmax be finite.We have, Lmin = imin rmin & Lmax = imax rmaxThe interval [Lmin, Lmax] is called the gray (intensity) scale.We shift this interval to interval [0, L-1], where, l = 0 is black & l = L-1 is white on grey scale.
Image Sampling & QuantizationIntensity resolution: smallest discernible change in intensity level.Image interpolation: process of using known data to estimate the values at unknown locations. Nearest neighbor interpolation: assigns intensity of nearest neighbor in original image. Bilinear interpolation: uses 4 nearest neighbors. Bicubic interpolation: uses 16 nearest neighbors.