Can't detect yellow colour using hsv method.

I've put together some codes that I found here so that it will function as I desire. I want the code to detect yellow colour using hsv method and draw a bound box around the yellow object. I've managed to get the code started but it won't detect the yellow colour or any other colour (I printed out a wheel of colour on paper and use it to test the code).

close all
clear all
clc
vid=videoinput('winvideo',1,'YUY2_160x120');
set(vid,'TriggerRepeat',Inf);
vid.returnedcolorspace='rgb';
vid.FrameGrabInterval=2;

start(vid)

while(vid.FramesAcquired<=200)
    data1=getdata(vid,1);
    hsvFrame = rgb2hsv( data1 );
    %sets all values for pixels that are not within the yellow range to zero.
    hsvFrame( hsvFrame( : , : , 1 ) > 0.2 ) = 0;
    hsvFrame( hsvFrame(: , : , 3) < 0.25 ) = 0;

      diff_m = find( hsvFrame( : , : , 1 ) ~=0 );

      bw= bwlabel(diff_m,8);
      stats=regionprops(bw,'BoundingBox','Centroid');

      imshow(data1)
       hold on
       for object=1:length(stats)
           bb=stats(object).BoundingBox;
           bc=stats(object).Centroid;
           rectangle('Position',bb,'EdgeColor','Y','LineWidth',2);
           plot(bc(1),bc(2),'-m+');
           a=text(bc(1)+15,bc(2),strcat('X:',num2str(round(bc(1))),'Y:',  num2str(round(bc(2)))));
           set(a,'FontName','Arial','FontWeight','bold','FontSize',12,'Color','yellow');
       end

       hold off
  end

stop(vid)

flushdata(vid);

clear all

Also if I set my camera resolution more than 160x120, it will cause some lag

Answer 1

[Jan]

Are you sure you want this:

hsvFrame( hsvFrame(: , : , 1) > 0.2  ) = 0;
hsvFrame( hsvFrame(: , : , 3) < 0.25 ) = 0;

Or should the 2nd line concern the 1st slice also?

What do you expect as output of the above commands? hsvFrame(: , : , 3) < 0.25 is a 2D logical array, while hsvFrame is 3D. Therefore you process the first slice only in both lines.

Using IMSHOW repeatedly is much slower than showing the image ones and updateing the CData property afterwards.

[Aliff]

fixed those

hsvFrame( hsvFrame(: , : , 1) > 0.2  ) = 0;
hsvFrame( hsvFrame(: , : , 3) < 0.25 ) = 0;

and converted it to

    hsvFrame( hsvFrame(: , : , 3) < 1 ) = 0;

I've tested in on an image and yields the desired result which I tested with an image instead with webcam. But when I tried it with the actual codes, it still doesn't do what its suppose to do. I notice that the bounding box is drawn on the left side of the screen, so it probably has something to do with the bounding box. I'm still unclear of the usage of CData.

[Jan]

About CData:

imageH = imshow(rand(200, 200, 3));
drawnow;
% Slow:
imshow(rand(200, 200, 3));
% Fast:
set(imageH, 'CData', rand(200, 200, 3));

"hsvFrame(:,:,3) < 1" is strange. The V value is limited to 1 in every case.

[Aliff]

Ok, i've tried using the CData, but I don't know if this the correct way to use it here:

data1 = imshow(rand(120, 160, 3));
drawnow;

I've ran the code and all i get is random noises in the image.

Answer 2

[Jan]

bwlabel operates on binary 2D images. So do not use

diff_m = find( hsvFrame( : , : , 1 ) ~=0 );   % BAD here
bw = bwlabel(diff_m,8)

but:

diff_m = hsvFrame( : , : , 1 ) ~=0;
bw = bwlabel(diff_m,8)