Digital Image Processing

Digital Image Processing STMIK MDP Digital Image Processing, Gonzalez & Woods

Digital Image Processing, Gonzalez & Woods

Image Distortion Model • Restoration depends on distortion • Common model: convolve plus noise • Special case: noise alone (no convolution) Digital Image Processing, Gonzalez & Woods

Thoughts on Restoration • Enhancement vs restoration • Enhancement: cosmetic • Restoration: substantive • In reality, there’s a continuum • Restoration relies on prior knowledge • Example of restoration • Inverse filtering • Noise removal • Nonlinear processing Digital Image Processing, Gonzalez & Woods

Chapter 6, Color Image Processing • Color fundamentals and models • Pseudocolor • Slicing • False-color maps • Index color • Multispectral color models • Color transformations • Smoothing and sharpening • Color segmentation Digital Image Processing, Gonzalez & Woods

Retinal Physiology and Color • Human retinas have (at least) four types of photoreceptors • Three types of ‘cones’ • High light level, high acuity vision • Each type of cone has a different spectral response • One type of ‘rods’ • Low-light level and peripheral vision • There is substantive genetic diversity in color receptors • Different spectral response of photoreceptor • Absence of one of the pigments • Many more phenomena... Digital Image Processing, Gonzalez & Woods

Spectral Response of Cones Digital Image Processing, Gonzalez & Woods

Color Matching Theory • Young’s observation • Any uniform color can be matched by projecting three different light sources onto a screen • In the 1920’s, an international effort on the part of a number of physicists let to the CIE standard color theory • The effort attempted to simplify and standardize • There have been many refinements, but the basic theory still stands • Theory useful for matching pigments (all paint stores have spectrophotometers) and design of color media systems Digital Image Processing, Gonzalez & Woods

Tristimulus Values Digital Image Processing, Gonzalez & Woods

Chromaticity Diagram • From http://www.efg2.com/Lab/Graphics/Colors/Chromaticity.htm • White is (1/3, 1/3, 1/3) • Y is the subjectiveintensity. Digital Image Processing, Gonzalez & Woods

Standard Observer Digital Image Processing, Gonzalez & Woods

Better Subjective Color • Constant distances in x, y space do not correspond to ‘constant’ changes of color • A better linear space is provided by the Y-U-V coordinates Digital Image Processing, Gonzalez & Woods

RGB Coordinates • With the advent of color television, the RGB coordinates were introduced to conveniently produce color on a color cinescope (cathode ray tube) Digital Image Processing, Gonzalez & Woods

RGB Gamut • Color space produced by a specific set of phosphors or LCD filters is limited Digital Image Processing, Gonzalez & Woods

Constant-Color-Difference Coordinates • For modulation (analog TV) and encoding (digital TV, JPEG), Y-U-V-like coordinates are produced • R’, G’, B’ are gamma corrected RGB. These are used in electronic media. Digital Image Processing, Gonzalez & Woods

Chapter 6 Color Image Processing Digital Image Processing, Gonzalez & Woods

Digital Image Processing