Assignment 28 — image manipulation

Due Monday, April 26

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Palette reduction module palette.py

• Implement functions distance() and closest(). Before defining their purposes, first some context.

• Historically, sometimes dvelopers to save computer memory for special purpose devices perform a palette reduction of colors used in image representation.

• Our reduction scheme will use an eight-color palette.

• Black, White, Red, Green, Blue, Yellow, Magenta, and Cyan; that is, (0, 0, 0), (255, 255, 255), (255, 0, 0), (0, 255, 0), (0, 0, 255), (255, 255, 0), (255, 0, 255), and (0, 255, 255)

• In a palette reduction, a pixel (r, g, b) is replaced by the pixel in in the palette to which it is closest.

• The distance between pixels (r1, g1, b1) and (r2, g2, b2) equals

abs(r1 - r2) + abs(g1 - g2) + abs(b1 - b2)

• Where abs() is a built-in function for calculating absolute values.

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Function distance( p1, p2 )

• Returns the distance between pixels p1 and p2; that is the sum of the red differences, green differences, and blue differences, where difference is an absolute value.

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Function closest( opixel )

• Make use of the color palette PALETTE8

PALETTE8 = [ ( 0, 0, 0), (255,255,255), ( 0,255, 0), ( 0, 0,255),

  (255, 0, 0), (255,255, 0), (255, 0,255), ( 0,255,255) ]

• Returns the pixel in PALETTE8 to which opixel is closest

• The module has built-in testing using a mandrill image.

• Possible strategy

• First make a legal guess for the result.

• Check each of the possibilites in PALETTE8, whenever you find a possibility that is better than the result, update the result.

 

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🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.