How can I crop several regions from a video and plot all the signals of rgb values in the same graph?

I have selected 3 regions from the first frame .Now I want to collect the rgb values for each region for the whole video and plot 3 different signals in a graph. However I am unable to do that.Here is the code that Ihave tried.

vid= VideoReader('respiration.mp4');

Fs= 6;

i=1;

j=0;

nof= vid.NumberOfFrames;

for k= 1:nof

img=read(vid,k);

if k==1

for c=1:3

[I,rect] = imcrop(img);

end

else

I = imcrop(img,rect) ;

end

r= I(:,:,1);

meanR(i)= mean(mean(r));

time(i)=j;

i=i+1;

j=j+(1/Fs);

end

figure(2)

plot(time,meanR)

grid on;

xlabel('time (seconds)');

ylabel('value of Red channel');

Answer 1

[Ameer Hamza]

Check this code

vid = VideoReader('respiration.mp4');

I = cell(1, 3);
rects = zeros(3, 4);
numFrames = vid.NumFrames; % good initial guess for pre-allocation
meanR = zeros(numFrames, 3); % The columns contain value for corresponding rectangles
time = zeros(numFrames, 1);

count = 1;
while hasFrame(vid)
    img = readFrame(vid);
    
    if count == 1
        for c = 1:3
            [I{c}, rects(c, :)]  = imcrop(img);
        end
    else
        for c = 1:3
            I{c} = imcrop(img, rects(c, :));
        end
    end
    
    for c = 1:3
        meanR(count, c)= mean(I{c}(:,:,1), 'all');
    end
    time(count) = vid.CurrentTime;
    
    count = count + 1;
end

[khadizatun suha]

Thank you so much for your help.It is working and showing 3 different signals . But can you please help me with showing the 3 seperate plots for each signal.Because I will need this signals for further application.It will be agreat help.

[Ameer Hamza]

You can use subplot.

subplot(3,1,1)
plot(meanR(:,1));
title('First cropped region')

subplot(3,1,2)
plot(meanR(:,2));
title('Second cropped region')

subplot(3,1,3)
plot(meanR(:,3));
title('Third cropped region')

[khadizatun suha]

Thank you so much ,once again. :D

[Ameer Hamza]

I am glad to be of help!