note on matrices, arrays, pixels

Author: Robert (Bob) Turner

episodes/02-image-basics.md

@@ -75,6 +75,16 @@ let's start our exploration with 15 pixels in a 5 X 3 matrix with 2 colours and
 work our way up to that complexity,
 but first the necessary imports.
 
+> ## Matrices, arrays, images and pixels
+> The **matrix** is mathematical concept - numbers evenly arranged in a rectangle. This can be a two dimensional rectangle, 
+> like the shape of the screen you're looking at now. Or it could be a three dimensional equivalent, a cuboid, or have 
+> even more dimensions, but always keeping the evenly spaced arrangement of numbers. In computing, **array** refers 
+> to a structure in the computer's memory where data is stored in evenly-spaced **elements**. This is strongly analogous 
+> to a matrix. A `numpy` array is a **type** of variable (a simpler example of a type is an integer). For our purposes, 
+> the distinction between matrices and arrays is not important, we don't really care how the computer arranges our data 
+> in its memory. The important thing is that the computer stores values describing the pixels in images, as arrays. And 
+> the terms matrix and array can be used intechangably.
+{: .callout}
 ~~~
 """
  * Python libraries for learning and performing image processing.*