168 471 Computer Graphics, KKU. Lecture 9

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Antialiasing

Aliased 'W' Antialiased 'W'

digitized

Analog line Digital line: aliasing occurs

jaggies

168 471 Computer Graphics, KKU. Lecture 9

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Antialiasing

- What anti aliasing attempts to do is, using mathematics, fill i

n some of the digital system w - ith colors that are in between t he two adjoining colors. In this

case a medium gray would be between the black and the whi

te. Some gray squares placed in the grid might help soften u

p the "jaggies"

168 471 Computer Graphics, KKU. Lecture 9

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Antialiasing

168 471 Computer Graphics, KKU. Lecture 9

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Unweighted Area Sampling

• Intensity is proportional to the amount of area covered.• Defining the box weighting function which has volume of 1 (Imax).• Determine the overlap volume Ws [0, 1].•

168 471 Computer Graphics, KKU. Lecture 9

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Weighted Area Sampling

168 471 Computer Graphics, KKU. Lecture 9

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Antialiasing in Practice

• Use of low pass filter by summing products between the mask coefficients and the intensities of the pixels under the mask.• For w which is a 3x3 mask, the response R at the center of the mask is

R = w1z1 + w2z2 + … + w9z9

RR

maskmask

168 471 Computer Graphics, KKU. Lecture 9

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Antialiasing in Practice

(a) (b)