Unpacking tuples of pixels : I've been trying to solve this textbook question for a while but am a bit stuck.

Question:

We have provided a module image with a procedure file2image(filename)
that reads in an image stored in a file in the .png format. Import this procedure and invoke it,
providing as argument the name of a file containing an image in this format, assigning the returned
value to variable data

The value of data is a list of lists, and data[y][x] is the intensity of pixel (x,y). Pixel
(0,0) is at the bottom-left of the image, and pixel (width-1, height-1) is at the top-right.
The intensity of a pixel is a number between 0 (black) and 255 (white).
Use a comprehension to assign to a list pts the set of complex numbers x+yi such that the
image intensity of pixel (x, y) is less than 120.

Here is the relevant method that was provided

    def file2image(path):
    """ Reads an image into a list of lists of pixel values (tuples with
        three values). This is a color image. """
    (w, h, p, m) = png.Reader(filename = path).asRGBA() # force RGB and alpha
    return [_flat2boxed(r) for r in p]

I'm really unsure how to parse the 3 values as a comprehension, anyone has a guess?