How to label the blank space in a image ?

Hi.I have a problem in identifying an object in a image. I have 9 squares organized like a matrix,3x3,in each square I can have the letter X,number 0 or blank space.I managed to identify the X and 0 with bwlabel and OCR but I can't think of a solution to identify the blank space.If I can recognize the blank space then I can predict if the winner will be X or 0.Any ideas? This image is pretty similar with the images i'm working Image Example . Thanks.

[Adam]

Surely if there are only 3 options and you can identify two of them then whatever is left is the 3rd option?

[Cyrus]

If you can figure out the number of items in each row or each column, you can subtract it from 3 and get the number of blank spaces.

[Chiriac Andrei]

@Mohammad Taheri,yes,i can find the number of blank spaces but i need the position,not the numbers. @Adam if the line is completely empty,or just 1 x or 0 there how can i figure out if the X/0 it's on (0,1) position,(0,2) or (0,3) ?

[Adam]

Well I don't know how you are identifying it, but I assumed that such identification would come with a location, otherwise how does it count as being identified?

Answer 1

[Cyrus]

Here you go:

The matrix named Blank_Matrix has the location of blank squares as 1; else the value is 0.

clear all; close all; clc;

I = imread('xsio.gif');
figure(), imshow(I), title('Input Image')
impixelinfo

Crop_Begin_X = 7;
Crop_Begin_Y = 21;
Width = 219; %%Col
Height = 219; %%Row

%%Cropping the Image.
Cropped_Image =  imcrop (I, [Crop_Begin_X, Crop_Begin_Y, Width, Height]);

figure(), imshow(Cropped_Image), title('Cropped_Image')
impixelinfo

%%Convertnig to Black and White
BW_Image = im2bw(Cropped_Image);
figure(), imshow(BW_Image), title('BW_Image')
impixelinfo

[Row, Col] = size(BW_Image);

Crop_Begin_X = 7;
Crop_Begin_Y = 21;
Width = 219; %%Col
Height = 219; %%Row

Blank_Matrix = zeros(3, 3);
Matrix_Row = 0; 
Matrix_Col = 0;

Width_of_the_Square = 72;

y=1;
while y + Width_of_the_Square <= Col 
    Matrix_Col = Matrix_Col+1;
    Matrix_Row = 0;
    fprintf('Matrix_Col = %d\n', Matrix_Col);
        x = 1;
        while  x + Width_of_the_Square <=  Row
            Matrix_Row= Matrix_Row+ 1;
            fprintf('Matrix_Row = %d\n\n', Matrix_Row);
            TMP_title = ' Not Blank' ;
            Square =  imcrop (BW_Image, [x, y, 72, 72]);

              Number_of_White_Pixels = 0;
              for i = 1 : Width_of_the_Square
                  for j = 1 : Width_of_the_Square
                      if Square(i, j) == 1
                          Number_of_White_Pixels = Number_of_White_Pixels + 1;
                      end
                  end
              end

              if Number_of_White_Pixels >= 4500
                  TMP_title = 'Blank';
                  Blank_Matrix(Matrix_Col, Matrix_Row) = 1;
              end

              hold on
              figure()
              imshow(Square), title(TMP_title)
              pause(0.5);
              hold off

              x  =x + Width_of_the_Square;
          end
          y = y + Width_of_the_Square;      
  end

[Chiriac Andrei]

This is a good solution if the size of the squares are always the same but in my case,i forgot to mention, the squares will be handwritten on a board or a paper and the size will be different almost every time...