Displaying real time data is not efficient. Am I doing something wrong or is it app designer that is slow?

Hi,

I'm building a real time GUI in app designer to display 768 double pixel values from the thermal camera through serial communication at a frame rate of 16Hz. I am using the CData to update the image everytime instead of calling the imagesc in every loop, but this responds well only in 8hz not more than that and sometimes it hangs even at 8hz. Further more in the program I'm also saving the read data in the .csv file (inclusion or deleting of which doesn't cause any difference in the speed of the program) before going to the display part. What is that I'm doing wrong here? Or is there any alternative way which does this more efficiently. Thanks for your time and patience in advance.

Below is the code that I'm making use of.

properties (Access = private)
      filename='C:\Users\kmana\Desktop\Matlab\Serial_Read.csv';
        fileID ;
        pixData=zeros(1,768);%store every pixel data
        mPktCnt =0;
        imData=zeros(24,32); %matrix to store whole image data
    end




function startupFcn(app)
            I=  imagesc(app.imData,'Parent',app.UIAxes);
            colormap(app.UIAxes,jet(256));
             % colorbar(app.UIAxes);
            delete(instrfindall);   %pre-emptively close all ports
            s1 = serial('COM8');    %define serial port to read the Arduino
            s1.BaudRate=115200;     %define baud rate
            s1.InputBufferSize=2^21; % increase the buffer size 
            s1.Terminator = 'CR';    % set the terminator to that on arduino
            fopen(s1);           
            s1.ReadAsyncMode = 'continuous';
            app.fileID = fopen(app.filename,'w'); % open csv file to store the data
            
            while(s1.BytesAvailable <= 0)  %wait until Arduino outputs data
                
            end
            
            while(1)
                
                sSerialData = fscanf(s1); 
                temp = strsplit(sSerialData,','); 
                % reading the pixel data converting it into double and storing it in the pixData array and then in the csv file
                for j=1:768   
                   app.pixData(j) = str2double(temp(j));
                    fprintf(app.fileID, '%2.2f,', app.pixData(j));
                end
                fprintf(app.fileID, '\n');
%                app.mPktCnt= app.mPktCnt+1;
%                 app.mPktCnt
                 % converting pixData array into 24X32 matrix which is stored in imData
                  for k=1:24
                     for l=1:32
                         app.imData(k,l)=app.pixData(((k-1)*32)+l);
                     end
                 end
                   % use this imData to update the CData of imagesc.
                   I.CData(:)= app.imData(:);                
                  pause(0.001);
                 %drawnow;
            end

[Walter Roberson]

It is more efficient to sscanf all of sSerialData at one time than to str2double() one item at a time from it.

[Image Analyst]

Try uncommenting the drawnow so that it updates at each iteration, if that's what you want. Otherwise it might only update whenever it thinks it has enough time to do it.

[Kavya Managundi]

Dear Walter, you have been my saviour since the day I sarted working on Matlab. I knew sscanf was more efficient and even tried implementing it earlier in normal matlab program but somehow I had not succeeded to use it and when I shifted to app designer I totally forgot that might have been an issue here. Thank you for pointing it out to me!

[Kavya Managundi]

Dear image Analyst, I have commented drawnow because it slows down the interface even drawnow limitrate that's why I shifted to pause(0.001) but do you think it produces wrong results?

[Kavya Managundi]

I have a new problem now. At 16Hz the code works perfectly fine but it works for ony 5 minutes and starts causing the delay again.

[Steven Lord]

for k=1:24
  for l=1:32
    app.imData(k,l)=app.pixData(((k-1)*32)+l);
  end
end

Try replacing this with reshape, possibly with a transpose as well.

Have you used the Profiler to determine what part of this code is the bottleneck? Is it displaying the image on the screen or the disk access?

[Kavya Managundi]

Dear Steven, pause(0.001) consumes most of the time when I replace it with drawnow it is even worst.

[Walter Roberson]

Try

drawnow limit