understanding the letter recognition sample of OpenCV

1

BenNG
61 ●2 ●6

Eduardo
3589 ●1 ●15 ●41

Hi all,

I try to understand the letter recognition sample of OpenCV and i'm stuck on this line

        int cls_label = responses.at<int>(i) - 'A';

Can somebody explain what this line means ? more precisely what this 'A' is doing here ?

Thank you !

Comments

Ok. I think that the image samples are only 'A'

BenNG (Sep 29 '16)edit

2

berak
32993 ●7 ●81 ●312

data in that example is read from this csv file , which has letters for labels in the 1st column.

subtracting 'A' from those makes 0-based labels again, since:

'A' - 'A' = 0, 'B' - 'A' = 1, 'C' - 'A' = 2, etc.

1

'A' means ascii code of A as integer. output of the code below is 35 ( 100 - 65 )

   int a = 100;
   a = a - 'A';
   std::cout << a;