gamma.py

for x in range(width):
    for y in range(height):
        r, g, b = image.getpixel((x, y))

        r_ = 255 * (r/255)**gamma
        g_ = 255 * (g/255)**gamma
        b_ = 255 * (b/255)**gamma

        new_pixel = (int(r_), int(g_), int(b_))
        new_image.putpixel((x, y), new_pixel)