LECTURE NOTES 
                                 ON 
                DIGITAL IMAGE PROCESSING 
                                    
                                    
                              PREPARED BY 
                      DR. PRASHANTA KUMAR PATRA 
              COLLEGE OF ENGINEERING AND TECHNOLOGY, BHUBANESWAR 
                          
                          
                          
                          
                          
                          
                          
                          
                          
                          
                                  1 
         
                             
                            Digital Image Processing 
          
                                  UNIT-I 
                DIGITAL IMAGE FUNDAMENTALS AND TRANSFORMS 
          
          
           1. ELEMENTS OF VISUAL PERCEPTION 
           1.1 ELEMENTS OF HUMAN VISUAL SYSTEMS 
          
             •  The following figure shows the anatomy of the human eye in cross section 
          
          
          
          
          
          
          
          
          
          
          
          
             •  There are two types of receptors in the retina 
                 –   The rods are long slender receptors 
          
                 –   The cones are generally shorter and thicker in structure 
             •  The rods and cones are not distributed evenly around the retina. 
             •  Rods and cones operate differently 
                 –   Rods are more sensitive to light than cones. 
          
                 – At low levels of illumination the rods provide a visual response called 
                    scotopic vision 
          
                 – Cones respond to higher levels of illumination; their response is called 
                    photopic vision 
          
                                       2 
          
                     Rods are more sensitive to light than the cones. 
                  
                                                     Digital Image Processing 
                  
                  
                  
                  
                  
                  
                  
                  
                  
                  
                  
                  
                  
                  
                                                                                                                                      
                                                                                                                                      
                  
                         •  There are three basic types of cones in the retina 
                         •  These cones have different absorption characteristics as a function of wavelength 
                             with peak absorptions in the red, green, and blue regions of the optical spectrum. 
                         •  is blue, b is green, and g is red 
                     Most of the cones are at the fovea. Rods are spread just about everywhere except the 
                     fovea 
                  
                            There is a relatively low sensitivity to blue light. There is a lot of overlap
                  
                  
                  
                                                                          3 
                  
         
                        Digital Image Processing 
         
                                 4