MATLAB: How to count number of iterations.

auto-thresholding algorithmiterationloopsave data

 I = imread('Coins.jpg');
Id = im2double(I); % I is a uint8 grayscale image
T = 0.5*(min(Id(:)) + max(Id(:)));
deltaT = 0.01; % convergence criterion
done = false;
 while done
g = Id >= T;
Tnext = 0.5*(mean(Id(g)) + mean(Id(g)));
done = abs(T - Tnext) < deltaT;
T = Tnext;
end

i want to count number of iteration for this program.! as well i want to store value of T at each iteration.!

Best Answer

count = 0
newT = zeros(1,100); % Try to presize to something big enough to hold all iterations if you can estimate it
while done
   g = Id >= T;
   Tnext = 0.5*(mean(Id(g)) + mean(Id(g)));
   count = count + 1;
   newT(count) = Tnext
   done = abs(T - Tnext) < deltaT;
end

Presize newT if you can come up with a sensible bounded estimate, otherwise the warning you get is likely irrelevant anyway. Your code will be a little slower, but unlikely to matter in this case.

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MATLAB: While loop isn’t working

You have two mistakes

1. while loop should work with a scalar condition, but as far as I know if you use a logical vector it will only enter the loop if all values are true:

% endless loop - as expected
while true
    disp(rand(1));
end
% never enters loop - as expected
while false
    disp(rand(1));
end
% endless loop
while [true true]
    disp(rand(1));
end
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    disp(rand(1));
end
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So when you declared x as a vector 1x50 you booby trapped your loop. just initialize x to the x_0 value

x = x_0;

2. In your loop condition you checked if the value is smaller than the tolerance value instead of larger, so naturally it will never enter the loop unless by luck you started from zero:

while abs(f(x)) > epsilon T % should work

MATLAB: Iterative threshold selection on an input gray-level image

You need to save T into an array that is indexed by the loop iteration counter. Like this:

clc;    % Clear the command window.
clearvars;
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 20;
grayImage = imread('coins.png');
subplot(2, 2, 1);
imshow(grayImage);
title('Original Image', 'FontSize', fontSize);
% Let's compute and display the histogram.
[pixelCount, grayLevels] = imhist(grayImage);
subplot(2, 2, 2); 
bar(grayLevels, pixelCount); % Plot it as a bar chart.
grid on;
title('Histogram of original image', 'FontSize', fontSize, 'Interpreter', 'None');
xlabel('Gray Level', 'FontSize', fontSize);
ylabel('Pixel Count', 'FontSize', fontSize);
xlim([0 grayLevels(end)]); % Scale x axis manually.
Id = im2double(grayImage);
Imax = max(Id(:));
Imin = min(Id(:));
T = 0.5*(min(Id(:)) + max(Id(:)));
deltaT = 0.01;
done = false;
counter = 1;
while ~done
  savedThresholds(counter) = T;
  
  g = Id >= T;
  Tnext = 0.5*(mean(Id(g)) + mean(Id(~g)));
  done = abs(T - Tnext) < deltaT;
  T = Tnext;
  
  % Display g
  subplot(2, 2, 3);
  imshow(g);
  title('Binary Image', 'FontSize', fontSize);
  
  % Plot savedThresholds
  subplot(2, 2, 4);
  plot(savedThresholds, 'b*-', 'MarkerSize', 15, 'LineWidth', 2);
  grid on;
  title('Thresholds', 'FontSize', fontSize);
  xlabel('Iteration', 'FontSize', fontSize);
  ylabel('Threshold', 'FontSize', fontSize);
  % Enlarge figure to full screen.
  set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
  
  promptMessage = sprintf('Threshold for iteration %d is %f.\nDo you want to Continue processing,\nor Quit processing?', ...
    counter, savedThresholds(counter));
  titleBarCaption = 'Continue?';
  buttonText = questdlg(promptMessage, titleBarCaption, 'Continue', 'Quit', 'Continue');
  if strcmpi(buttonText, 'Quit')
    return;
  end
  
  % Increment loop interation counter.
  counter = counter + 1;
end

Best Answer

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MATLAB: While loop isn’t working

MATLAB: Iterative threshold selection on an input gray-level image

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