from PIL import Image

im = Image.open('116GR.png')
pix = im.load()

w, h = im.size

for x in xrange(w):
    for y in xrange(h):
        rgb = list(pix[x,y])

        for k in xrange(3):
            rgb[k] = (rgb[k]&3) * (255/4)

        pix[x,y]=tuple(rgb)

im.save('out.png')