Contrast Adjustment

Problem

Adjust the contrast of a grayscale image around the midpoint 128.

Each pixel becomes clamp(round(128 + alpha * (v - 128)), 0, 255), returned as an integer. alpha = 1 leaves the image unchanged and alpha < 1 reduces contrast.

Test cases

case 1

in: [[[0,100],[200,255]],1.5]

expected: [[0,86],[236,255]]

case 2

in: [[[0,128,254]],0.5]

expected: [[64,128,191]]

case 3

in: [[[10,20],[30,40]],1]

expected: [[10,20],[30,40]]

case 4

in: [[[0,64,192,255]],2]

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

Starter codePython

def adjust_contrast(image, alpha):
    # Your code here
    pass

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