Find the diameter of fruit image in matlab

I want to find the diameter of an binary image. Here i my code, but it makes some error:

img= imread('apple.png');
im1=rgb2gray(img);

%level=graythresh(img);
%BW=im2bw(img,level);

level=graythresh(im1);
BW=im2bw(im1,level);

%obtain the edge of the image
e=edge(im1,'canny',0.52);

%get the size of the image
[m n]=size(e);
i1=0;
j1=0;

%i & j varies from 1 to size of the image
for i=1:m
    for j=1:n
        if(e(i,j)==1)
            %0 for black pixel and 1 for white
            %only white pixel enters the if loop position of the white 
            %pixel are stored in a variable i1 & j1
            k2=e(i,j);
            i1=i;
            j1=j;
            break
        end
    end
    break 
end

k=1;
k1=1;
for i=1:m
    for j=1:n
        if(e(i,j)==1)
            disi(k)=abs(i-i1);
            disj(k1)=abs(j-j1);
            k=k+1;
            k1=k1+1;
        end
    end
end

maxi=max(disi);
imagesc(img(:,:,1));
r1=img(:,:,1);
g1=img(:,:,2);
b1=img(:,:,3);
m1=mean2(g1);
m2=mean2(r1);
m3=mean2(b1);
r2=m2/(m1+m2+m3);
if(r2>0.4)
    c=1;
end

subplot(331), imshow(img);
subplot(332), imshow(im1);
subplot(333), imshow(e);
subplot(334),imshow(r2);

Can anyone help me out, how can i find the diameter from an binary image.

[Matt J]

but it makes some error:

We need you to post that error, and also to provide apple.png so we can try to reproduce it.

[Rupok Kumar]

Here is my apple image. I have found the boundary of my apple shape but having some problem with calculate the diameter.

I have seen a paper according to implement it. Here I attached the link:

 <http://dl.matlabproject.ir/form/files/576270.pdf>

Answer 1

[Gopichandh Danala]

You can use regionprops to find many properties of BW.

 props = regionprops(BW,'EquivDiameter');
  % equiv diameter of a circle of same area
  equiv_diameter1 = [props.EquivDiameter];

In case if you want to do this yourselves use find, pdist to compute max cord_length (diameter)

% raw way to find max chord length for irregular object
[row, col, ~] = find(BW);
all_cords = [row, col];
max_chordLength  = max(pdist(all_cords));

[Rupok Kumar]

Could you help, how can i show this image from here:

k=1;
k1=1;
for i=1:m
    for j=1:n
        if(e(i,j)==1)
            disi(k)=abs(i-i1);
            disj(k1)=abs(j-j1);
            k=k+1;
            k1=k1+1;
        end
    end
end

[Image Analyst]

I don't see an image there. Are you talking about (the poorly named) e? If so, just do

imshow(e);

Anyway, why not simply use bwdist()?

[Rupok Kumar]

Its from my question code. But here:

%i & j varies from 1 to size of the image
for i=1:m
    for j=1:n
        if(e(i,j)==1)
            %0 for black pixel and 1 for white
            %only white pixel enters the if loop position of the white 
            %pixel are stored in a variable i1 & j1
            k2=e(i,j);
            i1=i;
            j1=j;
            break
        end
    end
    break 
end

i showed the image as

imshow(e);
And i found the boundary of my image.

Now i want to show this image from here:

k=1;
k1=1;
for i=1:m
    for j=1:n
        if(e(i,j)==1)
            disi(k)=abs(i-i1);
            disj(k1)=abs(j-j1);
            k=k+1;
            k1=k1+1;
        end
    end
end

[Gopichandh Danala]

I don't recommend the way you wrote the code and your code doesn't have the formula to compute Euclidean distance.

From my understanding and in the way you are expecting this is what you are looking for:

%%I think this is what you are planning to do (not recommended)
% Get all cordinates where the pixel value is 1
[nrow, ncol] = size(img);
cords = double.empty();
for row = 1:nrow
    for col = 1:ncol
        if BW(row, col) == 1
            cords = [cords;[row,col]];
        end
    end
end
% Then compute all the distances between all points in cords manually
num_cords = length(cords);
all_dist = zeros(num_cords^2,1);
counter = 1;
for idx =  1:num_cords 
    for vals = 1:num_cords 
        all_dist(counter) = sqrt(abs((cords(idx,1)-cords(vals,1))^2 + (cords(idx,2)-cords(vals,2))^2));
        counter = counter + 1;
    end
end
max_D = max(all_dist);

But I recommend to use inbuilt functions matlab provides:

%%This can be simply done in many other efficient ways
% Image Analyst answer..
% BW2 = bwdist(BW);
% max_D2 = max(BW2(:));
% or..
% [row, col, ~] = find(BW);
% cords3 = [row, col];
% max_D3  = max(pdist(cords3));

Answer 2

[Image Analyst]

Not sure what you're after with your confusing code. The best I can figure is that you're trying to identify the boundary coordinates of the apple. If so, just threshold and call bwboundaries. It's like 2 lines of code. Here is a full demo with fancy displays and lots of comments. See the upper left image with the yellow outline around the apple.

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;

fullFileName = 'D:\Matlab\work\Tests\apple.png';
[folder, baseFileName, ext] = fileparts(fullFileName);

%=======================================================================================
% Read in demo image.
rgbImage = imread(fullFileName);
% Shrink it to speed it up
% rgbImage = imresize(rgbImage, 0.75);
% Get the dimensions of the image.
[rows, columns, numberOfColorChannels] = size(rgbImage);
% Display the original image.
subplot(2, 2, 1);
imshow(rgbImage, []);
axis on;
caption = sprintf('Original Color Image, %s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0.05 1 0.95]);
% Get rid of tool bar and pulldown menus that are along top of figure.
% set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off')

% Convert ot a grayscale image
grayImage = max(rgbImage, [], 3);
% Display the gray scale image.
subplot(2, 2, 2);
imshow(grayImage, []);
axis on;
caption = sprintf('Gray Image, %s', baseFileName);
title(caption, 'FontSize', fontSize, 'Interpreter', 'None');
drawnow;
hp = impixelinfo(); % Set up status line to see values when you mouse over the image.

% Histogram it
subplot(2, 2, 3);
histogram(grayImage);
grid on;
title('Histogram of Gray Image', 'FontSize', fontSize, 'Interpreter', 'None');

% Determine binary image mask.
mask = grayImage > 128; % Adjust number as necessary.
% Extract largest blob only.
mask = bwareafilt(mask, 1);

%=======================================================================================
% Display the image.
subplot(2, 2, 4);
imshow(mask, []);
axis on;
title('Mask Image', 'FontSize', fontSize, 'Interpreter', 'None');
hp = impixelinfo();
drawnow;

% bwboundaries() returns a cell array, where each cell contains the row/column coordinates for an object in the image.
% Plot the borders of all the blobs found in the mask image, on the original grayscale image using the coordinates returned by bwboundaries.
subplot(2, 2, 1); % Switch back to the original image in the upper left.
hold on;
boundaries = bwboundaries(mask);
numberOfBoundaries = size(boundaries, 1);
for k = 1 : numberOfBoundaries
  thisBoundary = boundaries{k};
  plot(thisBoundary(:,2), thisBoundary(:,1), 'y', 'LineWidth', 3);
end
hold off;