Posterize

Problem

Quantize a grayscale image to a fixed number of evenly spaced levels.

For each pixel, snap to the nearest level with index = round(v * (levels - 1) / 255), then map back with round(index * 255 / (levels - 1)). levels is at least 2 and outputs are integers in [0, 255].

Hint

Map to a level index first, then scale that index back to 0-255.

Test cases

case 1

in: [[[0,100],[200,255]],4]

expected: [[0,85],[170,255]]

case 2

in: [[[0,128,255]],2]

expected: [[0,255,255]]

case 3

in: [[[10,20,30],[240,250,255]],3]

expected: [[0,0,0],[255,255,255]]

Starter codePython

def posterize(image, levels):
    # Your code here
    pass

3 test cases · run your code against them in the editor