I am comparing the ball position and according to position i am sending string through serial communication to controller. But that program gives error at some times n some times run successfully

The error will occur at "if " condition, the error is giving below -:

" ??? Undefined function or method 'bc' for input arguments of type 'double'.

Error in ==> say2 at 48
     if (bc(1)<x1);  "

Could you give me the reason of this? I didn't get solution .

code is:-

clc;
clear all;
%program to detect red color only                                                         
vid = videoinput('winvideo',1,'YUY2_640x480');        % Capture the video frames using the videoinput function

% Set the triggring of the video object and getting frames
set(vid, 'FramesPerTrigger', Inf);
set(vid, 'ReturnedColorspace', 'rgb');
vid.FrameGrabInterval = 5;                           %setting interval between two frames

start(vid); %start the video aquisition here

data = getsnapshot(vid); 
 [a b c]= size(data);
    x=b; 
    x1=x/2-120;
    x2=x/2+120; 
    ser=serial('COM1');
fopen(ser);

while(1)                       %Set a loop that stop after 100 frames of aquisition
    data = getsnapshot(vid);                         % Get the snapshot of the current fram   
    flushdata(vid); 
% To track red objects in real time
% We have to subtract the red component 
% From the grayscale image to extract the red components in the image.
    diff_im = imsubtract(data(:,:,1), rgb2gray(data)); 
    diff_im = medfilt2(diff_im, [3 3]);            % median filter to filter out noise
    diff_im = im2bw(diff_im,0.18);                 % Convert the grayscale image into a binary image.
    diff_im = bwareaopen(diff_im,300);             % Remove all those pixels less than 300px
    bw = bwlabel(diff_im, 8);

    stats = regionprops(bw, 'BoundingBox', 'Centroid'); % Set the properties for each region
      imshow(data)
      hold on

      %Looping to bound the red objects in a bounding box.
      for object = 1:length(stats)
          bb = stats(object).BoundingBox;
          bc = stats(object).Centroid;
          double(bc)
          rectangle('Position',bb,'EdgeColor','r','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

       if (bc(1)<x1);
           disp('right') ,fprintf(ser,'R');
    elseif ((bc(1))>x2)
        disp('left') ,fprintf(ser,'L');
    elseif (x1<(bc(1))<x2)
        disp('forwd') ,fprintf(ser,'F');
    else
       disp('stop') ,fprintf(ser,'S');
    end

        hold off

end
stop(vid);                                       % Stop the video aquisition.

flushdata(vid);                                  % Flush all the image data stored in the memory buffer.

Answer 1

[Image Analyst]

Probably because there are no detected regions. Put this in before your "for" loop

if isempty(stats)
  return;
end