Issue with Spectrometer Snapping and GUI updating

Hey All

I'm currently working on a GUI to have a camera snapping a photo constantly processing it and then updating the plot on my gui. I've heard some stuff about using timers etc to fix the issue, but in all honesty, I have no clue how to get started. Could anyone give tips?

This is my code!

 function StartStopLiveSpectrumButtonValueChanged(app, event)
        % Load background average (if not already loaded)
        if ~isfield(app, 'bckgrnd_avg')
            load("Spectrometer_Settings.mat", "bckgrnd_avg");
            data = load("Spectrometer_Settings.mat");
            app.bckgrnd_avg = bckgrnd_avg;
        end
        
        % check if background photos have been snapped 
        pass = BackgroundPhotoExistenceCheck(app,"Live Spectrum");
        if pass ~= 1
            return
        end
        

        % Configure manual triggering
        triggerconfig(app.vid_ASI, 'manual');

        % Start the acquisition
        start(app.vid_ASI);

        % Init Wavelength
        % Extract the grating value
        grating = app.Spectrometer_gratting;
        
        % Loop through all fields in the loaded data
        fields = fieldnames(data);
        for i = 1:numel(fields)
            field_name = fields{i}; % Get the current field name
            field_value = data.(field_name); % Get the value of the current field
            
            % Check if the field value contains the grating value
            if contains(field_name, num2str(grating)) && contains(field_name,"max")
                wvlngth_end = field_value; 
            elseif contains(field_name, num2str(grating)) && contains(field_name,"min")
                wvlngth_start = field_value; 
            end
        end
        wvlength = linspace(wvlngth_start, wvlngth_end, size(app.vid_ASI.VideoResolution, 1));
        
        % Loop while button is pressed
        while app.StartStopLiveSpectrumButton.Value
            % Capture and process spectrum
            try
                % Trigger the camera and retrieve the frame
                trigger(app.vid_ASI);
                Emission_Reading_Img = getdata(app.vid_ASI, 1);
            
                [spectrum_sum] = app.MyFuncs.ASI_Live_Feed_Snapping(Emission_Reading_Img,app.bckgrnd_avg); 
            catch ME
                warning(ME.Identifier,'Failed to capture or process spectrum: %s', ME.message);
                break; % Exit the loop if an error occurs
            end
    
            % Update UI axes
            if isempty(app.PlotHandle) || ~isvalid(app.PlotHandle)
                app.PlotHandle = plot(app.Spectrometer_Plot, wvlength, spectrum_sum);
                xlabel(app.Spectrometer_Plot, 'Wavelength (nm)');
                ylabel(app.Spectrometer_Plot, 'Arb. Counts');
            else
                set(app.PlotHandle,'YData', spectrum_sum);
                drawnow limitrate; % Keep the GUI responsive
            end
        end
        % Stop the acquisition when the loop ends
        stop(app.vid_ASI);

        % Flush the buffer to remove any leftover frames
        flushdata(app.vid_ASI);

Answer 1

[Anushka]

Hi @Bera,

As you have correctly mentioned about continuously updating the GUI, but using a while loop in a 'callback' function can make the app unresponsive. Instead, using a 'timer' is a better approach.

Below are the steps how can implement the 'timer':

1. Create a 'timer' in the App Startup or Initialization:

• Define a 'timer' object that runs at a fixed interval.
• Set the execution mode to 'fixedRate' so it continuously executes at a set period.
• Assign a 'callback' function to capture and process images.

2. Start the 'timer' on the Button Press:

• Start the 'timer' when the button is pressed.
• Stop the 'timer' when the button is released.

Here is the modified code using 'timer' that you can refer to:

1. Add this to your app properties:

properties(Access=private)
    TimerObj
end

2. Modify your button callback:

function StartStopLiveSpectrumButtonValueChanged(app, event)
    if app.StartStopLiveSpectrumButton.Value
        app.TimerObj = timer('ExecutionMode', 'fixedRate', ...
            'Period', 0.1, ...
            'TimerFcn', @(~,~) UpdateLivePlot(app));
        start(app.TimerObj);
    else
        stop(app.TimerObj);
        delete(app.TimerObj);
    end
end

3. Define the UpdateLivePlot function:

function UpdateLivePlot(app)
    try
        trigger(app.vid_ASI);
        Emission_reading_img = getData(app.vid_ASI, 1);
        spectrum_sum = app.MyFuncs.ASI_Live_Feed_Snapping(Emission_reading_img, app.bckgrnd_avg);
        
        if isempty(app.PlotHandle) || ~isvalid(app.PlotHandle)
            app.PlotHandle = plot(app.Spectrometer_Plot, app.wvlength, spectrum_sum);
            xlabel(app.Spectrometer_Plot, 'Wavelength(nm)');
            ylabel(app.Spectrometer_Plot, 'Arb.Counts');
        else
            set(app.PlotHandle, 'YData', spectrum_sum);
            drawnow limitrate;
        end
    catch ME
        warning('Failed to capture or process spectrum: %s', ME.message);
    end
end

You can refer to the given documentation link to know more about 'timer':

https://www.mathworks.com/help/matlab/ref/timer.html

Hope this helps!

[Bera]

Thank you so much, I will give these two a go and see if they work :)

Answer 2

[Raag]

Hi Bera,

Yes, using timers is a viable approach. At present, the while loop you previously implemented may run indefinitely because the condition based on "isStarting" will not update until the callback function completes its execution, resulting in an endless loop. Here's how you can get started with the timer method:

The first thing to do is using the button callback logic to manage the timer and camera operations:

function StartStopLiveSpectrumButtonValueChanged(app, event)  

    isStarting = app.StartStopLiveSpectrumButton.Value;    

    if isStarting  

        % Start camera  

        triggerconfig(app.vid_ASI, 'manual');  

        start(app.vid_ASI);  

        % Create timer  

        app.AcquisitionTimer = timer( ...  

            'ExecutionMode','fixedSpacing', ...  

            'Period',0.2, ...  % e.g., acquire data 5 times per second  

            'TimerFcn',@(~,~) acquireAndUpdatePlot(app) );  

        start(app.AcquisitionTimer);  

    else  

        % Stop timer if it exists  

        if ~isempty(app.AcquisitionTimer) && isvalid(app.AcquisitionTimer)  

            stop(app.AcquisitionTimer);  

            delete(app.AcquisitionTimer);  

            app.AcquisitionTimer = [];  

        end  

        % Stop camera  

        stop(app.vid_ASI);  

        flushdata(app.vid_ASI);  

    end  

end 

Next, you can define the 'acquireAndUpdatePlot' function for handling the image acquisition and plotting, as shown below:

function acquireAndUpdatePlot(app)  

    try  

        trigger(app.vid_ASI);  

        Emission_Reading_Img = getdata(app.vid_ASI, 1);  

        spectrum_sum = app.MyFuncs.ASI_Live_Feed_Snapping(Emission_Reading_Img, app.bckgrnd_avg);  

        % Update plot  

        if isempty(app.PlotHandle) || ~isvalid(app.PlotHandle)  

            app.PlotHandle = plot(app.Spectrometer_Plot, app.WavelengthAxis, spectrum_sum);  

            xlabel(app.Spectrometer_Plot, 'Wavelength (nm)');  

            ylabel(app.Spectrometer_Plot, 'Arb. Counts');  

        else  

            set(app.PlotHandle, 'YData', spectrum_sum);  

            drawnow limitrate;  

        end  

    catch ME  

        warning('Acquisition:Error', '%s', ME.message);  

    end  

end 

For more details on using timers in MATLAB, you can refer to the timer documentation: https://www.mathworks.com/help/matlab/ref/timer.html

[Bera]

Thank you so much, I will test using these :)

[Bera]

@Raag

I implemented this stuff before the code, it shouldn't affect it right? (For the button evaluaded code chunk)

   % Load background average (if not already loaded)
        if ~isfield(app, 'bckgrnd_avg')
            load("Spectrometer_Settings.mat", "bckgrnd_avg");
            data = load("Spectrometer_Settings.mat");
            app.bckgrnd_avg = bckgrnd_avg;
        end
        
        % check if background photos have been snapped 
        pass = BackgroundPhotoExistenceCheck(app,"Live Spectrum");
        if pass ~= 1
            return
        end
        

        % Init Wavelength
        % Extract the grating value
        grating = app.Spectrometer_gratting;
        
        % Loop through all fields in the loaded data
        fields = fieldnames(data);
        for i = 1:numel(fields)
            field_name = fields{i}; % Get the current field name
            field_value = data.(field_name); % Get the value of the current field
            
            % Check if the field value contains the grating value
            if contains(field_name, num2str(grating)) && contains(field_name,"max")
                wvlngth_end = field_value; 
            elseif contains(field_name, num2str(grating)) && contains(field_name,"min")
                wvlngth_start = field_value; 
            end
        end
        app.wvlength = linspace(wvlngth_start, wvlngth_end, size(app.vid_ASI.VideoResolution, 1));
        

[Bera]

@Raag

I keep getting this error?

Any clue why?

Warning: Cannot trigger OBJ while Logging is set to on.

Warning: Operands to the logical AND (&&) and OR (||) operators must be convertible to logical scalar values. Use the ANY or ALL

functions to reduce operands to logical scalar values.

> In Raster_SpecificQD_LEDFinderGUI/acquireAndUpdatePlot (line 302)

In Raster_SpecificQD_LEDFinderGUI>@(~,~)acquireAndUpdatePlot(app) (line 1608)

In timer/timercb (line 90)

>>

[Raag]

@Bera

You can certainly load the background average and compute the wavelength before you start the timer. As long as it all happens before you call 'start(app.AcquisitionTimer)', your timer callback will have everything it needs.

Regarding the “Cannot trigger OBJ while Logging is set to on” warning, it typically appears if the camera is already in a logging mode that conflicts with manual triggering. Stopping the camera, configuring the trigger mode, and then restarting often resolves it. For example:

stop(app.vid_ASI);
triggerconfig(app.vid_ASI, 'manual');
start(app.vid_ASI);

Finally, the “Operands to the logical AND (&&) and OR (||) operators must be convertible to logical scalar values. Use the ANY or ALL” message suggests you have something like 'if someVector && someCondition', where 'someVector' is non-scalar. MATLAB wants '&&' and ' || ' to work only with single true/false values, so you may need to wrap 'someVector' in an 'all(...)' or 'any(...)' function to ensure it reduces to a single logical value.

[Bera]

@Raag Hey Raag thank you so much for the quick response. I will give that recommendation a go and see if it works! Should I call

stop(app.vid_ASI);
triggerconfig(app.vid_ASI, 'manual');
start(app.vid_ASI);

in the same function as the button valuched changed function (so same spot as where the Is starting code comes up)

[Raag]

@Bera

Yes, placing those three lines '(stop, triggerconfig, and start)' in the same button callback function is perfectly fine, right before you begin the timer-based acquisition.

[Bera]

okay okay, thank you so much!

[Bera]

@Raag

I just had the chance to test it and it still isn't working for some reason.

This is the error message I am getting

> In Raster_SpecificQD_LEDFinderGUI/acquireAndUpdatePlot (line 304)

In Raster_SpecificQD_LEDFinderGUI>@(~,~)acquireAndUpdatePlot(app) (line 1615)

In timer/timercb (line 90)

In timer/start (line 67)

In Raster_SpecificQD_LEDFinderGUI/StartStopLiveSpectrumButtonValueChanged (line 1616)

In matlab.apps.AppBase>@(source,event)executeCallback(ams,app,callback,requiresEventData,event) (line 62)

Warning: Cannot trigger OBJ while Logging is set to on.

Warning: Arrays have incompatible sizes for this operation.