"TypeError: 'int' object is not iterable" when I was trying to use getpixel() in python

Question

I was trying to run a python script (python 2.6) which contains the code as below

import Image

def is_grey_scale(img_path="lena.jpg"):
    im = Image.open(img_path)
    w,h = im.size
    for i in range(w):
        for j in range(h):
            r,g,b,_ = im.getpixel((i,j))
            if r != g != b:
                return False

    return True

It is reporting error as defined below.

r,g,b, _ = im.getpixel((i, j))
TypeError: 'int' object is not iterable

Can you please let me know what is the error here.

Answer 1

The situation is as follows

You are trying to unpack result returned from im.getpixel((i, j)) into 4 variables r, g, b, _.

For this to work, the im.getpixel has to return a list, a tuple or another iterable, which will provide just 4 values for the variables. Providing more or less makes a problem.

But in your case, the function im.getpixel((i, j)) is returning an int, which is not by any means an iterable, so it complains.

Answer 2

The definition of the method is.

    def getpixel(self, xy):
        """
        Returns the pixel value at a given position.

        :param xy: The coordinate, given as (x, y).
        :returns: The pixel value.  If the image is a multi-layer image,
            this method returns a tuple.

Is your image a "multi-layer image" ? I assume its the same image used all over image processing Courses. Lena on wikipedia