IEG4160_Part2 - IEG 4160: Image and Video Processing....

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Digital Image Fundamentals IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu Light Visual perception Image sensing and acquisition Image sampling and quantization Basic relationships between pixels Linear and nonlinear operations
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Page 2 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Light Light is the electromagnetic radiation that can be seen and sensed by the human eye, with EM wavelength of 350nm to 780nm. Visible light region of the EM Ultraviolet Infrared
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Page 3 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Light Perceived color by the eye ± White (gray level): the reflected light by some body is relatively balanced in all visible wavelengths ± Color : the reflected light is in a limited range of the visible spectrum Three quantities describing a light source ± Radiance : amount of energy flowing from the light source (watt/m 3 ) ± Luminance : measured amount of energy an observer perceives from the light source (lumen/m 2 ) ± Brightness : a subjective descriptor of light perception (difficult to measure)
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Page 4 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Visual perception Unfortunately ± The human visual system is not well understood ± For judging the quality of an image, no objective measure human subjective assessment ± No "typical" human observers Nevertheless ± Some important insights from perceptual psychology
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Page 5 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Visual perception The Eye ± Two photoreceptors on the retina: rods & cones ± Rods : ~100 million; sensitive to dim light ± Cones : ~6.5 million; sensitive to color, bright light ± Image formation Focal length x 17 100 15 x = Optical nerve Fovea
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Page 6 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Visual perception The light intensity incident on the eye is not linearly proportional to the subjective brightness Can perceive a large range of intensity Brightness adaptation: cannot operate over such a range simultaneously Can perceive only a much smaller range simultaneously at a level Rods: dim-light vision Cons: bright-light vision
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Page 7 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Visual perception Just Noticeable Difference (JND) D varies with the background intensity I Weber’s law: D / I = a constant, over a large range
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Page 8 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Visual perception Mach Band Effect (in 1865) ± undershoots and overshoots around the boundary of regions of different intensities
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Page 9 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Visual perception Simultaneous contrast
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Page 10 IEG 4160: Image and Video Processing. Lecturer: Jianzhuang Liu 2. Digital Image Fundamentals Visual perception Optical illusions
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IEG4160_Part2 - IEG 4160: Image and Video Processing....

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