Extracting data from scanned documents from predefined tables with known position
I have a table, for example, a 5x5 grid on a piece of paper. In each box in that grid there is something written (doesn't matter what).
What I need is to extract that data from that grid. I created that grid/table so I exactly know its position, its rotation, etc. I have read some materials, and also a few questions on SO so I know the basic steps to recognise and extract data.
I would like to know, can the fact that I know the position of grid/table (since I created it) help me in the process of recognising it?
Also, small additional question. I noticed that in a process of creating binary image people mostly create inverted black and white image (i.e. black text becomes white, paper becomes black). Why? I know it probably helps the detection, but I am interested in a reasons. I cannot see why would the value 0 be better that 255 or vice versa. Both are extremes, just opposite. Maybe if you can point to some papers or similar.
e.g. findContours() expects white things on black bg
As @berak mentioned. Also I assume the reason why 255 (white) is used for data, is probably due to the similarity of binary data. 0 = no data, 1 = data. So in this case black means no data.