Homework 25 — image manipulation

Due Wednesday November 28

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Modules color.py and locate.py

• In classes 34 and 35 we investigated the power of patterns and made use of them to simplify image manipulation. In these classes we considered and developed modules

• manip.py

• Provides a pattern for photo manipulation and a collection of convenience fuctions to support blueing, color inversion, flipping, mirroring, mono coloring, greyscaling, sepia toning, and palette reduction.

• dim.py

• Provides functions to return the dimensions of two types of image manipulation — same size and clockwise rotation

• locate.py

• Provides functions for determining where is the source pixel for a pixel manipulation supported by manip.py

• color.py

• Provides functions for the pixel manipulations supported by manip.py

• The task at hand is to implement module color.py functions: greyscale(), sepia_tone() and reduce_palette() and module locate.py function ccw().

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Grayscaling — color.py function grey( p )

• In converting an image to its grayscale equivalent the translation sacrifices pixel coloring for intensity. In the conversion, a pixel p equal to (r,g,b) corresponds to a pixel (m,m,m) where m is the integer cast of

.299r + .587g + .114b

The formula is known as the NTSC formula.

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Sepia — color.py function sepia( p )

• 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 — color.py functions distance( p ) and simplify( p )

• 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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Clockwise rotation locate.py function ccw( spot, w, h )

• In a clockwise rotation an image is rotated by 90 degrees.

 

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© 2019 Jim Cohoon

Resources from previous semesters are available.