Matrix output from for loop showing only last iteration values

I'm doing a blob analysis to track droplete ejected in my experimental images. I am tracking the centroids of the blobs analyzed in each frame. In each frame, the number of blobs/bounding boxes are different and keeps on changing. The output I wish to obtain is the [X,Y] centroid of all the blobs in each frame, over all frames. I am using a for loop to run over the frames and hBlob Analysis to get the blob estimates. However, I am only getting the centroid data for the last frame. I am not sure how to output the centroids of all blobs in each frame to a common output variable, especially given that the number of blobs in each frame is not the same. Any help woudl be deeply appreciated. The code currently I am using is attached below.

for k = startImage:endImage

s = [sourcePath,s1,num2str(k),s2];

A = imread(s);

B = imread('Background.jpg');

S = imsubtract(B,A);

AA = imcrop(S,[0,0,1280,80]);

T = im2bw(AA,0.2);

Z = bwareaopen(T,50);

hBlobAnalysis = vision.BlobAnalysis('MinimumBlobArea',0,'MaximumBlobArea',300);

[objArea,objCentroid,bboxOut] = step(hBlobAnalysis,Z);

I = insertShape(AA,'Rectangle',bboxOut,'Linewidth',2);

numObj(k) = numel(objArea);

NUM(k,1) = numObj(k);

if numObj(k) == 0

objCentroid = [0 0];

else

xlswrite('centroid.xlsx',objCentroid);

end

imshow(I);

end

Answer 1

[Image Analyst]

You need to index it with the frame number, like

[objArea,objCentroid(frameNumber, 1:2),bboxOut] = step(hBlobAnalysis,Z);

[Dheeraj Cherukat]

Hi Image Analyst,

Could you please reply on the question asked on the below link. Your comments and gtuidance would highly appreciated please.

https://www.mathworks.com/matlabcentral/answers/654418-how-can-i-feed-a-thrsholded-image-after-thermal-image-processing-as-an-input-to-a-sun-tracking-syst#comment_1149088