why am I receiving this error code when plotting motion over time?

Hi I am using this code to plot motion over time in 2021b matlab:

% Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 14;
vidObj = VideoReader('hand.MOV');
numberOfFrames = vidObj.NumFrames;
% numberOfFrames = 10 % For making testing quicker
xPaddle = nan(1, numberOfFrames);
yPaddle = nan(1, numberOfFrames);
xDot = nan(1, numberOfFrames);
yDot = nan(1, numberOfFrames);
for frameIndex = 1 : numberOfFrames
	frame = read(vidObj, frameIndex);
	subplot(2, 3, 1);
	imshow(frame)
	axis('on', 'image');
	caption = sprintf('Original Image Frame %d of %d', frameIndex, numberOfFrames);
	title(caption, 'fontSize', fontSize);
	drawnow;
	% Convert to gray scale
	grayImage = rgb2gray(frame);
	% Crop frame to get rid of white window to the right.
	grayImage = grayImage(:, 1 : 500); % You need to determine the column
	subplot(2, 3, 2);
	imshow(grayImage)
	axis('on', 'image');
	impixelinfo;
	caption = sprintf('Gray Scale Image Frame %d of %d', frameIndex, numberOfFrames);
	title(caption, 'fontSize', fontSize);
	drawnow;
	
	%========================================================
	% First find the white paddle.
	% Threshold or call imbinarize()
	paddleMask = imbinarize(grayImage);
	% Fill holes
	paddleMask = imfill(paddleMask, 'holes');
	% Take largest blob only.  That's the white paddle
	paddleMask = bwareafilt(paddleMask, 1);
	% We need to shrink the paddle because the edges are less bright and they
	% get detected when we try to get the dot.  So let's explude edges.
	se = strel('disk', 15, 0);
	paddleMask = imerode(paddleMask, se);
	subplot(2, 3, 3);
	axis('on', 'image');
	imshow(paddleMask)
	impixelinfo;
	title('Paddle Mask', 'fontSize', fontSize);
	drawnow;
	% Find centroid of white paddle.
	props = regionprops(paddleMask, 'Centroid');
	% Skip it if the paddle can't be found, like it's too dark or something.
	if isempty(props)
		continue;
	end
	% Get x and y
	xPaddle(frameIndex) = props.Centroid(1);
	yPaddle(frameIndex) = props.Centroid(2);
	%========================================================
	%  Now get the black dot.
	thresholdValue = 220;
	blackBlobs = grayImage < thresholdValue;
	% Erase junk outside the paddle
	blackBlobs = blackBlobs & paddleMask;
	% Erase the axle.
	blackBlobs(104:157, 264:319) = false;
	% Note, black dot might not be resolved enough to find it!
	% Take blobs only if they're in the 2-50 pixel range.
	% That should get us the black dot.
	props = regionprops(blackBlobs, 'Centroid', 'Area');
	allAreas = [props.Area];
	blackBlobs = bwareafilt(blackBlobs, [2, 70]);
	% Sometimes there is noise, and we get 2 blobs, so just take the largest blob in that range.
	blackBlobs = bwareafilt(blackBlobs, 1);
	subplot(2, 3, 4);
	imshow(blackBlobs)
	impixelinfo;
	axis('on', 'image');
	title('Black Dot', 'fontSize', fontSize);
	drawnow;
	% Find centroid of black dot.
	props = regionprops(blackBlobs, 'Centroid', 'Area');
	allAreas = [props.Area];
	% Skip it if the dot can't be found, like it's too blurred or something.
	if isempty(props)
		fprintf('No dot found on frame #%d of %d.\n', frameIndex, numberOfFrames);
		continue;
	end
	% Get x and y
	xDot(frameIndex) = props.Centroid(1);
	yDot(frameIndex) = props.Centroid(2);
	subplot(2, 3, 5:6);
	plot(xDot, 'b.-', 'LineWidth', 1, 'MarkerSize', 15);
	hold on;
	plot(yDot, 'r.-', 'LineWidth', 1, 'MarkerSize', 15);
	grid on;
	title('Black Dot.  X = Blue, y = red', 'fontSize', fontSize);
	xlabel('Frame Number', 'fontSize', fontSize);
	ylabel('Column or Row', 'fontSize', fontSize);
	if frameIndex == 1
		% Maximize the figure window.
		g = gcf;
		g.WindowState = 'maximized';
	end
	drawnow;
end
% Interpolate any missing ones.
missingIndexes = isnan(xDot);
if any(missingIndexes)
	xFit = 1 : numberOfFrames;
	xDot = interp1(find(~missingIndexes), xDot(~missingIndexes), xFit, 'spline');
	yDot = interp1(find(~missingIndexes), yDot(~missingIndexes), xFit, 'spline');
	subplot(2, 3, 5:6);
	plot(xDot, 'b.-', 'LineWidth', 1, 'MarkerSize', 15);
	hold on;
	plot(yDot, 'r.-', 'LineWidth', 1, 'MarkerSize', 15);
	grid on;
	title('Black Dot.  X = Blue, y = red', 'fontSize', fontSize);
	xlabel('Frame Number', 'fontSize', fontSize);
% 	ylabel('Column or Row', 'fontSize', fontSize);
end
fprintf('Done running %s.m ...\n', mfilename);

I am recieving this error code:

No dot found on frame #1 of 375.

Intermediate dot '.' indexing produced a comma-separated list with 3 values, but it must produce a

single value when followed by subsequent indexing operations.

Error in motiontrackingandplotting (line 60)

xPaddle(frameIndex) = props.Centroid(1);

I believe this is due to my video but I am not sure what I should about my video that would resolve this error code. I cannot attatch the zip file because it is too large but here is figure 1 from the code showing the blobs and you can see that my hand is not detected:

How can I improve my video so that the code will detect my hand as the large blob. I have not yet added anything to be the smaller blob but will after I figure this part out.

[Sara K Takiguchi]

I am also confused on how to find the threshold value to isolate the two blobs from all the other junk in the background.

[Sara K Takiguchi]

Since the video was too big, I uploaded it as a yotube video. Here is the link:

https://youtube.com/shorts/pJwIaApa7zM?feature=share

The video is a bit different than the one I originally used so the red tape on my hand is what I want to be recognized as the black dot and I changed the threshold value to be 255 in the code to remove the white background.

This is what my figure looks like with the new video and it is not recognizing the tape but seems to be recognizing my hand.

The error code is:

No dot found on frame #1 of 334.

No dot found on frame #2 of 334.

No dot found on frame #3 of 334.

Intermediate dot '.' indexing produced a comma-separated list with 2 values, but it must produce a

single value when followed by subsequent indexing operations.

Error in motiontrackingandplotting (line 60)

xPaddle(frameIndex) = props.Centroid(1);

Answer 1

[Shree Charan]

Hi Sara,

In lines 59,60 and 93,94 ‘props’ is being dot indexed.

However, the ‘regionprops’ function returns a struct array (https://www.mathworks.com/help/images/ref/regionprops.html#buoixjn-4).

‘props’ contains multiple variables and hence by dot indexing it, you are trying to apply one index to multiple variables leading to the error “Intermediate dot '.' indexing produced a comma-separated list with 3 values, but it must produce a single value when followed by subsequent indexing operations”.

You may refer to this answer to understand this better: https://www.mathworks.com/matlabcentral/answers/1722130-intermediate-dot-indexing-produced-a-comma-separated-list-error-prevents-extracting-values-from?s_tid=answers_rc1-2_p2_MLT