I want to extract the point of interest from plotted graph?

I want to extract the point of interest i.e from negative to positive is 1st point of interest and positive to negative is 2nd point of interest. these points are marked with red outline in graph. for more information these plotted points are local minima points. after extraction i have to utilize the x-axis points to calculate the difference between them. can anyone help me out?

Code which i used to calculate average horizontal values and plotted minimas are:

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 =

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

locs =

    30
    34
    36
    50
    93
    97
   110
   121
   127
   136