中南大学医学图像处理英文课件 chapter 6 color image processing.pptVIP

Two principal factors to motivate the use of color 1) color is a powerful descriptor that often simplifies object identification and extraction from a scene 2) humans can discern thousands of color shades and intensities, compared to about only two dozen of shades of gray. When color is available, it gives much more information about an image than intensity alone. Color is very useful for recognition of objects in an image both for humans and computers. The actual color perceived by a human of an object depends on both the color of the illumination and the reflectivity of the object, as well as the sensitivity of human perception. Objects appear to be different colors because they absorb and reflect different colors of light. A blue object, for example, reflects blue light while absorbing other colors. Grey objects or grey images reflect and absorb all frequencies of light about equally, so they do not appear colored. The spectrum of chromatic light from about 400nm to 700nm Three basic quantities used to describe the quality of a chromatic light source: radiance, luminance, and brightness Color is sensed by the eye using three kinds of cones, each sensitive primarily to red, green or blue, though there is significant overlap. We refer to red, green and blue as the primary colors, and denote to set as RGB. blue = 435.8nm green = 546.1nm red = 700nm (CIE) RGB is only for the purpose of standardization, doesn’t mean that these three fixed RGB components can generate all spectrum colors. Secondary colors (the primary color of pigments or colorants) : magenta (red + blue), cyan (green + blue), and yellow (red + green) Mixing the three primaries, or a secondary with its opposite primary will produces white light. Mixing the three pigment primaries, or a secondary with its opposite pigment primary will produces black light. The characteristics generally used to distinguish one color from another are brightness, hue, and saturation (the later two t