How to extract the point of interests from the plotted graph?

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Usman 2015-11-18

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https://ww2.mathworks.cn/matlabcentral/answers/255926-how-to-extract-the-point-of-interests-from-the-plotted-graph

I have plotted the horizontal average values and calculate their local minimas point. Now i want to extract the point of interest which i have marked with outline in graph. I want to extract the x-axis values by using the local minimas point at that specified position. code to calculate and plot minimas is:

I1=imread('open.jpg');
I2=rgb2gray(I1);
figure, title('open');
plot(1:size(I2,1), mean(I2,2));
hold on
horizontalAverages = mean(I2 , 2);
plot(1:size(I2,1) , horizontalAverages)
[Minimas locs] = findpeaks(-horizontalAverages) 
plot(locs , -1*Minimas , 'r*')

Minimas after execution are:

Minimas =

-86.5647
-80.3647
-81.3588
-106.9882
-77.0765
-77.8235
-92.2353
-106.2235
-115.3118
-98.3706

locs =

I am interested in 2nd and 5th minima. at second minima first intensity change happens i.e. negative to positive and a 5th minima 2nd intensity change happens i.e. positive to negative. anyone can help me out?