[Tutor] Numpy unexpected result: subtraction of cell values

[Carnell, James E]

>
> I'm sure this is easy, but I am having a difficult time finding the 
> right search terms to find it on the Internet. Any help much 
> appreciated.
>
> 3 dimensional array(x,y,rgb) which is a PIL image into a numpy array 
> using 'asarray' function.
>
> I want to subtract the Red Value in an array cell from a neighboring 
> Red Value cell.
>
> >>> pictArray[39][4]                    #pixel at 39 4
> array([150, 140, 120], dtype=unint8)
>
> >>> pictArray[39][5]                    #pixel at 39 5
> array([160, 150, 120], dtype=unint8)
>
> >>> pictArray[39][4][0]                 #red pixel
> 150
>
> >>> pictArray[39][5[0]                  #neighboring red pixel
> 160
>
> >>> pictArray[39][4][0] - pictArray[39][5][0]
> 246  # <---------------  ???  vs -10
>
> How do I get the number -10? Does this have to do with the dtype?
>

It looks like you're re-typing from your terminal window into your
Compose window... your life (and ours!) will be simpler if you just cut
and paste. 

	- sorry I am at work and due to security reasons can't plug a
thumb drive in for copying copde from my laptop. I have corrected the
values above. 

	- pictArray[39][4][0] - pictArray[39][5][0] = 246  is where I am
getting stuck


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