Usage of Blkproc function in matlab

Hi all

My objective is that a binary image is divided into 7×7 equal blocks. We scan each of the resulting 49 blocks along both horizontal and vertical directions. In each such scan, we count the number of transitions (white to black and vice-versa).Thus, we obtain a 2 × 49 = 98 component transition feature vector corresponding to each character sample.

my function file f.m is as follows

function f
global countof021;
global countof120;
 countof021=0;
 countof120=0;
  for i = 1:3 
    for j= 1:4
      if ( (img(i,j)==1) && (img((i+1),j)==0) ) 
          countof120=countof120+1;
      elseif ( (img(i,j)==0) && (img((i+1),j)==0) ) 
          countof021=countof021+1;
     end    
   end
  end
end

My count of the 0 to 1 or 1 to 0 transition file is count120.m is as follows

clc;
close all;
clear all;
im1 =imread('D:\SAIGEETHA\ME\V SEMESTER\MINI PROJECT\000t01.tif');
[m,n]=size(im1);
resizedimage=imresize(im1,[343 343]);
img=resizedimage;
countof021=0;
countof120=0;
blockofimage=zeros(49);
dividedimage = blkproc(img,[7 7],@(x)f);
disp('img=');
disp(img);
disp('countof120=');
disp(countof120);
disp('countof021=');  
disp(countof021);

The error message is

??? Error using ==> f
Too many output arguments.

Error in ==> @(x)f

Error in ==> blkproc at 100
firstBlock = feval(fun,x,params{:});

Error in ==> count120 at 11
dividedimage = blkproc(img,[7 7],@(x)f);

Please help me to accomplish this .

Thanks

Saigeetha

Answer 1

[Walter Roberson]

The function you pass in to blkproc() must have an output argument. If you are not going to use the matrix blkproc() creates from the outputs of f, then return something like 0 and ignore the result afterwards.

There is no point in using blkproc() with that f, since that f ignores its inputs and the current location within the block and always calculates the same thing -- and always overwrites the global variables with the exact same calculated values. Besides, that f is going to crash because it attempts to access the variable "img" which is not defined within the scope of f.

Oh yes: variables are only global within routines that specifically declare them as global, so in your count120.m the variables countof021 and countof120 are going to be the local variables initialized to 0 earlier in count120.m

Remember, blkproc() is going to be run on all of the blocks before control is returned to any routine that might read out the global variables.

[Kaustubha Govind]

+1

I totally overlooked the application!

Answer 2

[Kaustubha Govind]

Try using it as blkproc(img,[7 7],@()f); and see if the error goes away. Since "f" does not have any output arguments, you don't need to specify the "x" in the parentheses.