Human Eye Two types of receptors on retina rods and cones CSE 332 564 Visualization Image Basics Kl Klaus M Mueller ll Computer Science Department Stony Brook University Rods spread all over the retinal surface 75 150 million low resolution no color vision but veryy sensitive to low light g Cones a dense array around the central portion of the retina the fovea centralis 6 7 million high resolution color vision but require brighter light Color Perception Tristimulus T i ti l Th Theory the eye has three types of color Color Spaces HSV CIE receptors Red Green Blue Color reproduction one can generate almost any color on a monitor by mixing three primaries RGB CRT monitor have 3 color guns RGB Hue color Saturation peak from white light V l overall Value ll integral i t l across all ll CIE L equal distances mean equal perceptive ti differences diff CIE LAB Space Digital Image Image 2D matrix of pixels Image g resolution number of pixels along each matrix dimension L Perceived brightness 300 150 75 37 resolution Each pixel has a value a single value if greylevel image a triple RGB if color image Dynamic Range Histogram Each pixel is represented by a number of bits Quantization process of discretizing a continuous value into bits Minimal number of bits 6 64 greylevels or 4 levels for R G B most medical digital images have 12 bits 4096 grey levels A hi histogram t counts t th the number b off pixels i l att each h greylevel l l h v number of pixels having grey value v total number of pixels partial bandwidth full bandwidth 8 bit bits 4 bit bits not enough bits leads to quantization artifacts and loss of resolution G d contrast Good t t requires i a histogram hi t with ith full f ll b bandwidth d idth Contrast Difference off b Diff brightness i ht iin adjacent regions of the image grey level luminance contrast color contrast Point Spread Function Each E h pixel i l iis nott a sharp h spike ik b butt represented by a point spread function PSF The PSFs overlap and form a continuous function for the eye Smaller PSFs give sharper images