Changing Values in Function

Dear Community,

I have attached below a function that is supposed to accept three inputs, and return two outputs. I am supposed to change the value of outputs. I have attached this function to my matlab script, but when I run the program. I get the following error:

Output argument "lowThreshold" (and maybe others) not assigned during call to "thresh".

Error in UsingThisThreshold (line 71)
[lowThreshold, highThreshold] = thresh(grayLevels, pixelCount, imageToThreshold);

function [lowThreshold, highThreshold] = thresh(grayLevels, pixelCount, imageToThreshold)

       % create the figure
       fontSize = 20;
       figure
       set(gcf, 'Position', get(0,'Screensize')); % Enlarge figure to full screen
       subplot(1,2,1)
       bar(grayLevels, pixelCount, 'BarWidth', 1, 'FaceColor', 'b');
       title('Histogram of Original Integer Image', 'FontSize', fontSize);
       xlim([0 max(grayLevels(:))]); % Scale x axis manually.
       grid on;
       subplot(1,2,2)
       imshow(imageToThreshold)
       title('Original Grayscale Image After Thresholding', 'FontSize', fontSize);
       % create the edit boxes
       %Edit boxes where the user inserts or changes data
       e0 = uicontrol('Style','edit','Position',[150 80 80 20],'String','15','Callback',@updateTxtBox);
       e1 = uicontrol('Style','edit','Position',[150 55 80 20],'String','500','Callback',@updateTxtBox);
       [row,col] = size(imageToThreshold);
       % define the callback
       function updateTxtBox(object,eventdata)
          lowThreshold = str2num(get(e0,'String'));
          highThreshold = str2num(get(e1,'String'));
          for i=1:row
              for j=1:col
                  if imageToThreshold(i,j) < lowThreshold
                      imageToThreshold(i,j) = 0;
                  else if imageToThreshold(i,j) > highThreshold
                          imageToThreshold(i,j) = 0;
                      end
                  end
              end
          end
          subplot(1,2,1)
          hold on;
          yAxisLimits = ylim();
          line([lowThreshold, lowThreshold], yAxisLimits, 'Color', 'r', 'LineWidth', 2);
          line([highThreshold, highThreshold], yAxisLimits, 'Color', 'r', 'LineWidth', 2);
          caption = sprintf(' Low Threshold = %.1f', get(e0,'String'));
          text(lowThreshold, 0.7*yAxisLimits(2), caption, 'Color', 'r', 'FontWeight', 'Bold', 'FontSize', 15);
          caption = sprintf(' High Threshold = %.1f', get(e1,'String'));
          text(highThreshold, 0.9*yAxisLimits(2), caption, 'Color', 'r', 'FontWeight', 'Bold', 'FontSize', 15);
       end
   end

Answer 1

[Thorsten]

It may help to define the variables outside to the local function

 % create the figure
  lowThreshold = 0; % assign dummy values
  highTreshold = 0;
  fontSize = 20;

Answer 2

[Star Strider]

It seems that ‘lowThreshold’ and ‘highThreshold’ are defined inside the ‘updateTxtBox’ function, but never returned from it. (While nested functions have access to variables in the function they are nested in, the reverse is not true. You have to return them as with any other function.)

I would assign them outside (before) ‘updateTxtBox’ and then, just to be safe, pass them as arguments to it.

[Hussam Ibrahim]

I see. Thanks. Also, I want these values to be changed and updated by the user. Essentially, both these values are the threshold values for an image. I want the user to be able to pick the value he/she wants by trying different values. Do you know how is that possible?

[Star Strider]

You already seem to be doing that with your ‘e0’ and ‘e1’ assignments, although I did not run your code so I am not certain.

I always use the inputdlg function, simply because it’s easier. That returns a cell, so you simply have to use cell addressing on the result to recover the string.

Example:

lowThreshc = inputdlg( ... );
lowTreshold = str2num(lowThreshc{:});

Note the curly brackets ‘{}’.

I would put all this before the ‘updateTxtBox’ function regardless of how you input them.

[Hussam Ibrahim]

Ok, I think this is working. I just have one problem. The dialog inputs are only showing once. I need this to be set up like the following workflow:

1- User enters values 2- The result shows, if he likes then these values will be passed on. if he doesn't like these values, he can input other values to view.

This is how my function is setup right now: function [lowThreshold, highThreshold] = thresh(grayLevels, pixelCount, imageToThreshold)

     % create the figure
     lowThreshold = 15; % assign dummy values
     highThreshold = 5000;
     fontSize = 10;
     figure
     set(gcf, 'Position', get(0,'Screensize')); % Enlarge figure to full screen
     subplot(1,2,1)
     imshow(imageToThreshold)
     title('Original Grayscale Image After Thresholding', 'FontSize', fontSize);
     subplot(1,2,2)
     bar(grayLevels, pixelCount, 'BarWidth', 1, 'FaceColor', 'b');
     title('Histogram of Original Integer Image', 'FontSize', fontSize);
     xlim([0 max(grayLevels(:))]); % Scale x axis manually.
     grid on;
     % create the edit boxes
     %Edit boxes where the user inserts or changes data
     %e0 = uicontrol('Style','edit','Position',[150 105 80 20],'String','15','Callback', @updateTxtBox); %Default value, but user can change it.
%      e0 = uicontrol('Style','edit','Position',[150 80 80 20],'Callback',@updateTxtBox);
%      e1 = uicontrol('Style','edit','Position',[150 55 80 20],'Callback',@updateTxtBox);
     lowThreshc = inputdlg('Enter your minimum Threshold value: ');
     highThreshc = inputdlg('Enter your maximum Threshold value: ');
     lowThreshold = str2double(lowThreshc{:});
     highThreshold = str2double(highThreshc{:});
     [row,col] = size(imageToThreshold);
     %e3 = uicontrol('Style','edit','Position',[150 20 80 20],'Callback',@updateTxtBox);
     %Edit box that needs to be updated only when the user inputs data in the previous edit boxes.
     %e4 = uicontrol('Style','edit','Position',[285 140 50 20],'Enable','off');
     % define the callback
     function updateTxtBox(object,eventdata)
        for i=1:row
            for j=1:col
                if imageToThreshold(i,j) < lowThreshold
                    imageToThreshold(i,j) = 0;
                else if imageToThreshold(i,j) > highThreshold
                        imageToThreshold(i,j) = 0;
                    end
                end
            end
        end
        hold on;
        yAxisLimits = ylim();
        line([lowThreshold, lowThreshold], yAxisLimits, 'Color', 'r', 'LineWidth', 2);
        line([highThreshold, highThreshold], yAxisLimits, 'Color', 'r', 'LineWidth', 2);
        caption = sprintf(' Low Threshold = %.1f', get(e0,'String'));
        text(lowThreshold, 0.7*yAxisLimits(2), caption, 'Color', 'r', 'FontWeight', 'Bold', 'FontSize', 15);
        caption = sprintf(' High Threshold = %.1f', get(e1,'String'));
        text(highThreshold, 0.9*yAxisLimits(2), caption, 'Color', 'r', 'FontWeight', 'Bold', 'FontSize', 15);
        hold off
        figure
        imshow(imageToThreshold, []);
        title('Original GrayScale Image after Applying the Threshold', 'FontSize', fontSize);
     end % updateTxtBox
 end  % myGui

[Star Strider]

With inputdlg, you would have to put the inputdlg calls in a loop. The function has the ability to display default values, so these could initially be set to zero, and subsequently be set to the previous values entered. That is how I would do it, anyway.