Identify the duration of zero values and count the number of such zero regions

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Reji G 2022-12-1

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https://ww2.mathworks.cn/matlabcentral/answers/1868253-identify-the-duration-of-zero-values-and-count-the-number-of-such-zero-regions

评论： Image Analyst 2022-12-1

采纳的回答： Davide Masiello

Hello,

I have a signal shown above.

First I want to identify the duration(length) of each zero valued regions represented as T, T1, T2, T3 etc., (You may generate any signal with zeroed region similar to my graph)
Count how many such zero valued regions are there in 1 sec(or within a specified time).

Any help interms of code is well appreciated. Thank you in advance.

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Answer 1

Davide Masiello 2022-12-1

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编辑：Davide Masiello 2022-12-1

在 MATLAB Online 中打开

Use regionprops

time = 0:100;

signal = rand(size(time));

signal([3:6,15:21,43:55,61:64,87:92]) = 0;

plot(time,signal)

r = regionprops(signal==0,"SubarrayIdx");

for k = 1:length(r)

time_indexes = r(k).SubarrayIdx{2};

durations(k) = time(time_indexes(end))-time(time_indexes(1));

end

durations

durations = 1×5

3 6 12 3 5

Obviously, the number of zero regions is the length of the array durations.

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Davide Masiello 2022-12-1

编辑：Davide Masiello 2022-12-1

在 MATLAB Online 中打开

data.csv

That's because it seems you don't have any set of consecutive zeros, but rather many isolated ones

T = readmatrix('data.csv');

time = T(:,1);

signal = T(:,2);

plot(time,signal)

find(signal==0) % indexes of signal array where signal is zero

ans = 4795×1

4372 4402 4411 4417 4418 4420 4422 4429 4430 4432

What you could do is define a threshold to define small values as equal to zero. Be careful, depending on the threshold value you might significantly change your signal.

thr = 0.5;

signal(signal > -thr & signal < thr) = 0;

plot(time,signal)

r = regionprops(signal==0,"SubarrayIdx");

for k = 1:length(r)

time_indexes = r(k).SubarrayIdx{1};

durations(k) = time(time_indexes(end))-time(time_indexes(1));

end

Because of the noise of your signal, it will still find single zero values or very small zero intervals, which I assume you don't want to see.

Set a new threshold defining that you want only intervals that are larger than a certain time span.

durations(durations<0.0005) = []
durations = 1×5
    0.0009    0.0011    0.0032    0.0012    0.0024

In this way, it finds only the intervals that you can see with the naked eye in the plot (in fact, it's five of them).

By fiddling around with the various thresholds, you can refine your code further.

Image Analyst 2022-12-1

在 MATLAB Online 中打开

Or, more simply

zeroRegions = (signal == 0); % Identify elements that are exactly 0.
% Throw out runs less than, say, 3 elements long.
zeroRegions = bwareaopen(zeroRegions, 3);
% Measure what's left (regions 3 or more elements long).
r = regionprops(zeroRegions,"Area");
durations = [r.Area] % Extract all run lengths from structure into vector.

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Identify the duration of zero values and count the number of such zero regions

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Identify the duration of zero values and count the number of such zero regions

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