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lec21-handout-6up - 6.003 Signals and Systems Lecture 21...

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6.003: Signals and Systems Lecture 21 November 24, 2009 1 6.003: Signals and Systems Sampling November 24, 2009 Sampling Conversion of a continuous-time signal to discrete time. t x ( t ) 0 2 4 6 8 10 n x [ n ] 0 2 4 6 8 10 We have used sampling a number of times before. Today: new insights from Fourier representations. Sampling Sampling allows the use of modern digital electronics to process, record, transmit, store, and retrieve CT signals. audio: MP3, CD, cell phone pictures: digital camera, printer video: DVD everything on the web Sampling Sampling is pervasive. Example: digital cameras record sampled images. x y I ( x, y ) m n I [ m, n ] Sampling Photographs in newsprint are “half-tone” images. Each point is black or white and the average conveys brightness. Sampling Zoom in to see the binary pattern.
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6.003: Signals and Systems Lecture 21 November 24, 2009 2 Sampling Even high-quality photographic paper records discrete images. When AgBr crystals ( 0 . 04 1 . 5 µ m) are exposed to light, some of the Ag is reduced to metal. During “development” the exposed grains are completely reduced to metal and unexposed grains are removed. Sampling Every image that we see is sampled by the retina, which contains 100 million rods and 6 million cones (average spacing 3 µ m) which act as discrete sensors. http://webvision.med.utah.edu/imageswv/sagschem.jpeg Check Yourself Your retina is sampling this slide, which is composed of 1024 × 768 pixels. Is the spatial sampling done by your rods and cones ade- quate to resolve individual pixels in this slide? Sampling How does sampling affect the information contained in a signal?
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