Get the losing data

this program for tracking red color in real time, i set 300 frames, I would like get the centroid of red masker and save them to center(300x2) for the next step. How can I set the center(k,:) = [161,121](the center of image) when I lost data.

Here is the code

redThresh = 0.25; % Threshold for red detection
vidDevice = imaq.VideoDevice('winvideo', 1, 'YUY2_320x240', ... % Acquire input video stream
                    'ROI', [1 1 320 240], ...
                    'ReturnedColorSpace', 'rgb');
                VidDevice.FrameRate = '30.0000';
vidInfo = imaqhwinfo(vidDevice); % Acquire input video property
hblob = vision.BlobAnalysis('AreaOutputPort', false, ... % Set blob analysis handling
                                'CentroidOutputPort', true, ... 
                                'BoundingBoxOutputPort', true', ...
                                'MinimumBlobArea', 400, ...
                                'MaximumBlobArea', 3000, ...
                                'MaximumCount', 1);
hshapeinsRedBox = vision.ShapeInserter('BorderColor', 'Custom', ... % Set Red box handling
                                        'CustomBorderColor', [1 0 0], ...
                                        'Fill', true, ...
                                        'FillColor', 'Custom', ...
                                        'CustomFillColor', [1 0 0], ...
                                        'Opacity', 0.4);
htextins = vision.TextInserter('Text', 'Number of Red Object: %2d', ... % Set text for number of blobs
                                    'Location',  [7 2], ...
                                    'Color', [1 0 0], ... // red color
                                    'FontSize', 12);
htextinsCent = vision.TextInserter('Text', '+      X:%4d, Y:%4d', ... % set text for centroid
                                    'LocationSource', 'Input port', ...
                                    'Color', [1 1 0], ... // yellow color
                                    'FontSize', 14);
hVideoIn = vision.VideoPlayer('Name', 'Final Video', ... % Output video player
                                'Position', [300 300 vidInfo.MaxWidth+20 vidInfo.MaxHeight+30]);
nFrame = 0; % Frame number initialization
center = [0 0];
k = 0;
A = [0 0];
%%Processing Loop
while(nFrame < 300);
    rgbFrame = step(vidDevice); % Acquire single frame
    rgbFrame = flipdim(rgbFrame,2); % obtain the mirror image for displaying
    diffFrame = imsubtract(rgbFrame(:,:,1), rgb2gray(rgbFrame)); % Get red component of the image
    diffFrame = medfilt2(diffFrame, [3 3]); % Filter out the noise by using median filter
    binFrame = im2bw(diffFrame, redThresh); % Convert the image into binary image with the red objects as white
    [centroid, bbox] = step(hblob, binFrame); % Get the centroids and bounding boxes of the blobs
    centroid = uint16(centroid); % Convert the centroids into Integer for further steps 
    rgbFrame(1:20,1:165,:) = 0; % put a black region on the output stream
    vidIn = step(hshapeinsRedBox, rgbFrame, bbox); % Instert the red box

       for object = 1:1:length(bbox(:,1)) % Write the corresponding centroids
            k = k+1
          if isempty(hblob)
              center(k+1,:) = [161 121];
           else
          centX = centroid(object,1); centY = centroid(object,2);
          center(k+1,:) = [centX centY];
          end
          vidIn = step(htextinsCent, vidIn, [centX centY], [centX-6 centY-9]); 
      end
      vidIn = step(htextins, vidIn, uint8(length(bbox(:,1)))); % Count the number of blobs
      step(hVideoIn, vidIn); % Output video stream
      nFrame = nFrame+1;
  end
  %%Clearing Memory
  release(hVideoIn); % Release all memory and buffer used
  release(vidDevice);
  % clear all;
  clc;

Answer 1

[Walter Roberson]

I would think that hblob is not going to be empty because it defines a behavior object rather than an image output. The centroid output from "step" might be empty -- but if it is, then length(bbox(:,1)) is going to be 0 and so the "for" loop would not be entered to have the existing isempty() encountered.

In your existing code, you should be assigning to centX and centY when you assign to center. Except, that is, for the fact that you won't get there if there are no blobs.

If the routine can even return an empty blob (e.g., if it is somehow tracking with memory from the previous step), then shouldn't you be looking at the bbox size rather than at hblob ? The bbox would be representing empty if its third or fourth element are 0, not if isempty() anything.