how to change a variable value in a while loop?

Hi, I have a while loop in my matlab code and one of the variables in the loop 'Threshold_Value' is intially set to 0.5, but i would like to use a slider button in my matlab graphical user interface to adjust this value from 0 to 3.5, This value is used to change the threshold on a binary image(making it darker or lighter).

I have created the slider and set the min and max values correctly. But when i try and change the values with the slider it apears to change the value of 'Threshold_Value' as i can see it printing out the new values of the slider, But it apears to have no affect on the binary image?

The problem seems to be that although the value for 'Threshold_Value' is being changed when i move the slider it does not update the value in the loop ?

main code i used shown below

% --- Executes on button press in start_pushbutton.
function start_pushbutton_Callback(hObject, eventdata, handles)
%initialize the flag variable
set(handles.start_pushbutton,'UserData',1); 

imaqhwinfo ('winvideo', 1);
video = videoinput('winvideo',1,'RGB24_640x480');
origimage = 0;  %initilises origimage

preview(video);

    Threshold_Value = 0.5
%while the flag variable is one, the loop continues  
while (get(handles.start_pushbutton,'UserData') ==1)

    origimage=getsnapshot(video);
  pause(0.005)
imgGray = rgb2gray(origimage); %Converts Image to GrayScale  

    Threshold_Value = noiseThreshold ;  %Changes senstivity   
imgB = im2bw(imgGray,noiseThreshold);  %converts to binary
  imshow(imgB); %displays binery image 
end

% --- Executes on slider movement.
function Slider_Callback(hObject, eventdata, handles)
% hObject    handle to Slider (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)

   Threshold_Value  = get(hObject,'Value')

Answer 1

[Matt Fig]

I don't see where in the loop you are retrieving the value of the slider. Each time through the loop you will have to retrieve the value of the slider and set Threshold_Value equal to it.

Even if you do this, it appears that you are setting Threshold_Value equal to noiseThreshold, which I am guessing is a function.

[jim]

Hi, thanks for the fast reply!.

The code 'Threshold_Value = get(hObject,'Value')' Gets the value of the slider (E.g 2).

Then in the while loop I have set 'Threshold_Value = noiseThreshold' which i hoped would update the value for the 'noiseThreshold' which is then used in the code 'imgB = im2bw(imgGray,noiseThreshold);' to change the threshold.

You mentioned you couldnt see where in my code i am retrieving the value, do you have any ideas how i could retrieve this new value?

Or did you mean i need to somehow put the slider button function within the while loop in order for it to update the value :S

[Matt Fig]

You are retrieving the value of the slider in its own callback, but that value for Threshold_Value has nothing to do with the value for Threshold_Value in another function. Each function has its own workspace, so the variables created in one function do not exist in another function.

You need to get the value of the slider each time through the loop. What is noiseThreshold? Is it a function? This code must surely error if it is not.

[jim]

noiseThreshold is just a variable i set to 0.5, I could have just replaced it with 0.5.

e.g imgB = im2bw(imgGray, 0.5); %converts to binary

But because i wanted to make the number changeable i called it noiseThreshold.

noiseThreshold = 0.5

e.g imgB = im2bw(imgGray, noiseThreshold); %converts to binary

So do you know of a way i can get the new value to change/update the noiseThreshold eat time the program loops?

Thanks a lot for the advice and help!!