grayscale image processing

[zyb1003]

from PIL import Image

img  = Image.open('grey.jpg')
width, height = img.size

for x in range(width):
    for y in range(height):
        pixel = img.getpixel((x,y))
        red   = pixel[0]
        green = pixel[1]
        blue  = pixel[2]
        grey  = (red + green + blue) // 3
        img.putpixel((x,y), (grey,grey,grey))

img.save("grey2.jpg", "jpeg")

hello, Thanks for reply. However, I don't understand your code that much. Why do you make grey=red+green+blue/3? What is this grey used for? And also, my aim is to find how many bright(greyscale value>200) pixels in a certain row which has most bright pixels.