PIL question about crop method

[John Salerno]

John Salerno wrote:
> Diez B. Roggisch wrote:
> 
>> Alternatively you can see it as boundary lines, in the order left, 
>> top, right, bottom.
>>
>> (10, 20, 30, 100)
> 
> So in the above, from where are the numbers being counted? 10 is ten 
> pixels from the left border of the image? 20 is twenty pixels from the 
> top border? But is 30 thirty pixels from the left or the right border of 
> the image? And is 100 one hundred pixels from the top or bottom?

I came up with this, is it correct:

(a,b)               (c,b)
     -----------------
     |               |
     |               |
     -----------------
(a,d)               (c,d)


So the tuple would be (a, b, c, d)?