MATLAB Answers

Lukas
0

how to compare 2 binary images pixel by pixel

Asked by Lukas
on 20 Mar 2014
Latest activity Commented on by Image Analyst
on 22 Nov 2016 at 15:32

hello i need help please.

how to compare 2 binary images pixel by pixel? by using "for" in function "compare"?

it show me error (under text) and i do not know how to solve it:

??? Cell contents reference from a non-cell array object.
Error in ==> compare at 4
        if BW1{a,b}==BW2{a,b}
Error in ==> com at 9
    if compare(BW1,BW2)>100

i have this code:

    if true
  n=1;
  p=2;
  i=1;
  max=100;
  while p <= max
BW1=im2bw(o{n},0.4);    % in "o" are colour pictures
BW2=im2bw(o{p},0.4);
      if compare(BW1,BW2)>100
          c{i}=o{p};
          n=p;
          p=p+1;
          i=i+1;
      else
          p=p+1;
      end
  end
    end

and function for compare:

    if true
     function [same] = compare( BW1, BW2 )
  for a=1:500
      for b=1:500
          if BW1{a,b}==BW2{a,b}
              same=same+1;
          end
      end
  end
  end
    end

  3 Comments

Deos cpoy and pstae no lenogr wrok on yuor cpmouetr?

You can check the difference using Euclidian distance.

test_img = imread('image1.bmp');
input_im = imread('image2.bmp');
minimum =1000;   
[row, col] = size(test_img(:,:,1));
distance = zeros(row, col);
 for xAxis = 1 : row          
     for yAxis = 1 : col
        distance(xAxis, yAxis) =   sqrt((input_im(xAxis, 1) - test_img(yAxis, 1)).^ 2 + (input_im(xAxis, 2) - test_img(yAxis, 2)).^ 2);
     end
 end 
if distance < minimum
        minimum = distance;
end

4 Answers

Answer by Walter Roberson
on 20 Mar 2014
 Accepted answer

Change to

if BW1(a,b)==BW2(a,b)

  2 Comments

so sipmle thank you :) and "{}" are using only if i want to save or copy components of matrix variable?

{} is used only to extract something that is in cell array, removing the cell layer. () is used for all other kinds of arrays, such as struct arrays, object arrays, numeric arrays, and char arrays. () is also used for cell arrays when the result is to be left as a cell layer.


Answer by Image Analyst
on 20 Mar 2014

Lukas, don't loop. It looks like you want to count the number of pixels that are true(1) in both images. If so, just do

bothTrue = BW1 & BW2;
NumPixels = sum(bothTrue(:));

I don't know what you're doing with the "c" and "o" cell arrays and what you're doing with p. It looks like p may likely end up being 100 ("max"). But DO NOT USE max AS THE NAME OF YOUR VARIABLE! max() is a built in function and you'll destroy it if you name your own variable that.

  7 Comments

yes it is good. thank you. and is it any way how to compare only one part(second half) of matrix (binary image)?

middleRow = ceil(size(BW1, 1)/2);
BW1BottomHalf = BW1(middleRow:end, :);

Then do whatever you want with this half sub-image.


Answer by Lukas
on 21 Mar 2014

I have this problem. i should to make pdf from video (turning pages of book) . So i try choose to every single page from video (without OCR). My plan is. in "o{}" are saved all frames from video. "n"," p" are variables for choosing frames for camparing. First frame is automatically saved to "c{1}". later i compare 2. and 3. frame. if they are same i compare 3. and 4. etc. while there will be 2 different frames(during turning pages every frame is different). ) Now i am finding two same frames (it is time while i am moving hand for turn next page) and save it to "c{2}". changing of reslution and converting to BW are for saving hardware (processor). I hope that this code is not so far from succes but a don not know what is wrong still

  0 Comments


Answer by Augustine Ekweariri on 22 Nov 2016 at 8:47

You can check the difference using Euclidian distance.

test_img = imread('image1.bmp');
input_im = imread('image2.bmp');
minimum =1000;   
[row, col] = size(test_img(:,:,1));
distance = zeros(row, col);
 for xAxis = 1 : row          
     for yAxis = 1 : col
        distance(xAxis, yAxis) =   sqrt((input_im(xAxis, 1) - test_img(yAxis, 1)).^ 2 + (input_im(xAxis, 2) - test_img(yAxis, 2)).^ 2);
     end
 end 
if distance < minimum
        minimum = distance;
end

  1 Comment

First of all, you made the common beginner mistake of swapping x and y with row and column. The first index of the image arrays is not the x coordinate. It's the y coordinate and it's deceptive to call the y coordinate of input_img "xAxis". If the image is not square and the number of rows is more than the number of columns, your code will throw an error. Like I said, it's a common mistake, so be careful about that.

Secondly the computation doesn't make sense. You're taking the "distance" between the delta of the first columns and the delta of the second columns. Not only doesn't that make sense, but it ignores all columns from 3 onwards.

Third, using minimum, which goes from a scalar to a 2-D array, is unneeded and never even used.

And finally the whole loop thing could be vectorized into a single line of code.


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