Finding peaks and troughs of sinusoidal from a Matrix and elements bounded within

Hello i have a matrix that consists of zeros and ones. It has 5 sinusodial shapes linked together as seen in the image attached. The yellow represents where the value of the matrix is one and the blue for zero. How do i find the peaks and troughs of each of this sinusodial shapes and the indices/elements(rows and columuns) bounded by each of these sinusodial shapes. Basically i should have something that gives the peak and trough for sinusodial one and then the elements within it

Answer 1

[jonas]

Since you did not attach the data, I had to start from your attached image. Therefore my x- and y-values are not scaled correctly. Basically you get the coordinates with find() and then findpeaks() to locate peaks and troughs. See attachment for results.

%%Fix binary image
RGB=imread('pic.png');
GRAY = rgb2gray(RGB);
threshold = graythresh(GRAY);
BW = im2bw(GRAY, threshold);

%Crop edges
BW=BW(5:end-10,60:end-30);
imshow(BW)

%%Find coordinates of ones
[y,x]=find(BW==1)

%%Find peaks and troughs
[~,locs1]=findpeaks(y.*-1,'minpeakprominence',20,...
    'minpeakdistance',50)
[~,locs2]=findpeaks(y,'minpeakprominence',20,...
    'minpeakdistance',50)

%%Plot data
figure;
plot(x,y,'-',...
    x(locs1),y(locs1),'-x',...
    x(locs2),y(locs2),'-x')

[Nkenna Amadi]

heres the data

[Nkenna Amadi]

thank you for your reply it looks just about right with just one little adjustment. The peaks and troughs should look something just like in the picture i just attached in this comment, represented by the thin black lines not the way your answer provided them to be. Thank you again. hope its much clearer.

[jonas]

I'm not sure what those lines represent. What do they extend to? One line is also curved, why is that?

[Nkenna Amadi]

its just meant to be straight lines. Hopefully the diagram ive attached gives more understanding

[jonas]

Try this. You can adjust the lines anyway you want.

%%Load data and crop image
data=load('trap.mat');
BW=data.Trap;
BW=BW(1:216,:)
imshow(BW)

%%Find data coordinates
[y,x]=find(BW==1)

%%Find Peaks and troughs
[~,locs1]=findpeaks(y.*-1,'minpeakprominence',5,...
  'minpeakdistance',5)
[~,locs2]=findpeaks(y,'minpeakprominence',5,...
  'minpeakdistance',5)

%%Fix lines length
xpeak=[x(locs1)-10,x(locs1)+10];
ypeak=[y(locs1) y(locs1)];

xtrough=[x(locs2)-20,x(locs2)];
ytrough=[y(locs2) y(locs2)];

%%plot
figure;;hold on
plot(x,y,'-')
plot(xpeak',ypeak','k--')
plot(xtrough',ytrough','r--')
set(gca,'Ydir','reverse')

[Nkenna Amadi]

thank you very much ! how do i find the elements within each of these 5 sinusoids?

[jonas]

Simple enough. The peak indices are stored in locs2 (troughs) and locs1 (peaks). So, to find the indices between the first two troughs, you can type:

wave1=x(locs2(1):locs2(2))

then for the next

wave2=x(locs2(2):locs2(3))

and so on. If you want the corresponding y-values, just change x to y.