how to find number of foreground pixel and background pixel of an english alphabet

I have to find number of foreground pixel and background pixel within in the boundingbox. For example the letter B ,If we draw the straight line 4-side of the letter B then it will create a rectangle box ,inside rectangle box letter B is there. Within in the bounding box I have to find number of foreground and background Pixel. This is my code:

 E = imread('1.jpg');

 label=graythresh(E);

 BW = im2bw(E,label);

 imshow(BW)

 L=bwlabel(E);

z=regionprops(L,'BoundingBox');

nBlackpixel = sum(z(:))

nWhitepixel = numel(z) - nBlack