from PIL import Image

#Attention au chemin vers l'image !!
MonImage = Image.open("P:\\SNT\\IMG\\tux_yoda.jpg")

Taille = MonImage.size

for c in range(Taille[0]):
    for l in range(Taille[1]):
        rgb = MonImage.getpixel((c, l))
        R = rgb[0]
        G = rgb[1]
        B = rgb[2]
        MonImage.putpixel((c, l), (R, 0, B))

MonImage.show()