DOC: Improved Image Representation

The description of an image representation was missing the
direction cosines all together.  Understanding the physical
representation of an image, and it's relationship with
the index representation is a crucial element that must
be documented.

Change-Id: I5a103f878f84b4385cdccc7f7d0cb32dc803ffb7
Merge topic 'EnhanceDirectionCosDocumentation'

e4c851f3 DOC: Improved Image Representation