# Hello everyone. For example, how to identify a specific point in an image in a moving video as follows. The required video is also uploaded in zip format. If you are interested, you can discuss with me. Thank you all very much.

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Wesley on 29 Mar 2021
Commented: Wesley on 1 Apr 2021
The video screenshot is as follows：
Wesley on 31 Mar 2021
@darovaHow to define the extreme point or inflection point of the edge has become a difficult point, and it is difficult to achieve this goal.

darova on 31 Mar 2021
Here is an example for extreme points: find points where derivative changes it's sign
clc,clear
x = 0:0.2:10;
y = sin(x);
dy = sign(diff(y)); % sign of derivative
c1 = abs(diff(dy)); % change of sign
ix1 = 1 + find(c1);
plot(x(ix1),y(ix1),'or')
line(x,y)
Inflection point is a point where curvature changes its sign
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Image Analyst on 1 Apr 2021
You have to be able to describe in words what is unique about the point(s) you want to find. Then you can develop an algorithm to find it(them). For example, the blob looks roughly like an upside down V and I want to find the highest point (lowest line or row number) of the dent in the bottom middle of the blob. If you have that, you can make an algorithm.

Image Analyst on 31 Mar 2021
The bounding box and centroid are easy - just call regionprops()
props = regionprops(binaryImage, 'Centroid', 'BoundingBox');
If you want any other locations, you'd have to somehow precisely define where they are. It depends on the shape. Are all the shapes like that arrowhead shape?
Wesley on 1 Apr 2021
I see. Thank you very much for your kind help.