Class 36 — November 26

Image visualization

I draw from the past – Wonder about the present – Think of the future

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Look both ways

• Back or ahead

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HW Downloads — do not download until asked to

• manip.py

• dim.py

• color.py

• locate.py

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Sepia

• There is no one formula for defining a Sepia pixel conversation. The one used here comes from Microsoft.

• For pixel (r,g,b), the Sepia conversion is (sr,sg,sb) where

sr, sg, sb = int( min( i, 255 )), int( min( j, 255 )), int( min( k, 255 )),

where i, j, k are

i = .393r + .769g + .189b

j = .349r + .686g + .168b

k = .272r + .534g + .131b

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Palette reduction

• Sometimes to save computer memory, software developers 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 it is closest to. The distance between pixels (r1,g1,b1) and (r2,g2,b2) equals

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

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© 2019 Jim Cohoon

Resources from previous semesters are available.