06-1 - Color image processing

06-1 - Color image processing - 4/28/2008 Color image...

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4/28/2008 1 C o l o r image processing: fundamentals Spring 2008 ELEN 4304/5365 DIP 1 by Gleb V. Tcheslavski: [email protected] http://ee.lamar.edu/gleb/dip/index.htm Preliminaries Color image processing is motivated by two main factors: 1. Color is a powerful descriptor simplifying object recognition. 2. We can distinquish between thousands of color shades and intensities, compared to about 20-30 values of gray. There are two major areas of color image processing: 1. Full-color processing – images are acquired with a full-color sensor (TV camera, color scanner); 2 Pseudocolor processing colors are assigned to a particular Spring 2008 ELEN 4304/5365 DIP 2 2. Pseudocolor processing – colors are assigned to a particular monochrome intensity or intensity range. Many methods discussed for processing of monochrome images are applicable to color images; other methods need reformulation.
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4/28/2008 2 Fundamentals of color Mechanisms of color processing by human brain are not completely understood. However, the physical nature of color can be formally expressed and modeled. Spring 2008 ELEN 4304/5365 DIP 3 1666: Sir Isaac Newton managed to pass a beam of white light through a glass prism and got a rainbow on the other side where each color blends smoothly into the next. Fundamentals of color Particular colors of the object as human perceive them are determined by the nature of light reflection properties of the object. A body reflecting light that is balanced in all visible wavelengths Spring 2008 ELEN 4304/5365 DIP 4 body reflecting light that is balanced in all visible wavelengths appears as white. A body reflecting more light in a particular range of wavelengths and absorbing light in other bands appears as colored. Note : creatures other than humans may (and do!) perceive colors in a completely different way than we do…
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4/28/2008 3 Fundamentals of color If the light is achromatic (no colors), its only attribute is its intensity (amount). Examples of achromatic light: images produced by a b&w TV set monochrome pictures (not necessary b&w!) Our discussion TV set, monochrome pictures (not necessary b&w!). Our discussion so far was limited to achromatic images. Chromatic light spans the EM spectrum from approximately 400 to 700 nm. The three basic quantities used to describe a chromatic light source are radiance (the total amount of energy from the source, W), luminance (energy an observer perceives from the source, lm: for Spring 2008 ELEN 4304/5365 DIP 5 example, an observer might barely perceive any light from a source radiating in an infrared region), and brightness (a subjective descriptor practically impossible to measure since it is associated to both the intensity and color sensation). Fundamentals of color Color sensitive sensors of human retina are cones. The total of 6-7 million of cones in a human eye in a human eye can be associated with one of three groups: red (~575 nm) sensitive (about 65 % of all cones), green 1965 Spring 2008 ELEN 4304/5365 DIP 6 (~535 nm – 33%), and blue (~445 nm – 2%) sensitive.
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This note was uploaded on 12/08/2010 for the course ELEN 4304 taught by Professor Staff during the Spring '08 term at Lamar University.

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06-1 - Color image processing - 4/28/2008 Color image...

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