05PictureEncoding2009

05PictureEncoding2009 - CS1315: Introduction to Media...

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CS1315: Introduction to Media Computation Picture encoding and manipulation
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We perceive light differently from how it is Color is continuous Visible light is wavelengths between 370 and 730 nm That’s 0.00000037 and 0.00000073 meters But we perceive light with color sensors that peak around 425 nm (blue), 550 nm (green), and 560 nm (red). Our brain figures out which color is which by figuring out how much of each kind of sensor is responding One implication: We perceive two kinds of “orange” — any spectral distribution that hits our color sensors just right Dogs and other simpler animals have only two kinds of sensors They do see color. Just less color.
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Luminance vs. Color We perceive borders of things, motion, depth via luminance Luminance is not the amount of light, but our perception of the amount of light. We see blue as “darker” than red, even if same amount of light. Much of our luminance perception is based on comparison to backgrounds, not raw values. Luminance perception is color blind . Different parts of the brain perceive color and luminance.
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Digitizing pictures into dots We digitize pictures into many tiny dots Looks continuous to the eye Our eye has limited resolution Our background/depth acuity is particularly low Each picture element is a pixel i.e. “picture element”
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Pixels Pixels are picture elements Each pixel object “knows” its color E.g. given a pixel, a Python function can get the color of it. It also “knows” where it is in the picture E.g. given a pixel and a picture, a Python function can find out where the pixel is located in the picture
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matrix of pixels It is not a continuous line of elements, that is, a 1-D array A picture has two dimensions: Width and Height We need a 2-dimensional array: a matrix Just 2 x 2 image or matrix. 0 1
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05PictureEncoding2009 - CS1315: Introduction to Media...

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