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.

The video screenshot is as follows：

[darova]

Which point do you want to identify?

[Wesley]

It is mainly the centroid point, the extreme point or the inflection point.

[Wesley]

1. Make the following definition

function d = tracking(video)
% Function: Track and display the moving target in the video
% Input: video-video to be tracked
% Output: d-difference image sequence

% Read in video images
if ischar(video)
    avi = aviread(video);
    pixels = double(cat(4,avi(1:2:end).cdata))/255;
    clear avi
else
    pixels = double(cat(4,video{1:2:end}))/255;
    clear video
end
% Convert RGB image to grayscale image
nFrames = size(pixels,4);
for f = 1:nFrames
   pixel(:,:,f) = (rgb2gray(pixels(:,:,:,f)));  
end
 [rows,cols]=size(pixel(:,:,1));
nrames=f;
% Make difference between two adjacent frames and convert the difference image into a binary image
for l = 2:nrames
d(:,:,l)=(abs(pixel(:,:,l)-pixel(:,:,l-1)));
k=d(:,:,l);
   bw(:,:,l) = im2bw(k, .2);
   bw1=bwlabel(bw(:,:,l));
   imshow(bw(:,:,l))
   hold on
% 标记运动物体的位置并显示
cou=1;
for h=1:rows
    for w=1:cols
     if(bw(h,w,l)>0.5)
      toplen = h;
           if (cou == 1)
            tpln=toplen;
         end
         cou=cou+1;
      break
     end
     end
end
disp(toplen);
coun=1;
for w=1:cols
    for h=1:rows
     if(bw(h,w,l)>0.5)
        
      leftsi = w;
     if (coun == 1)
            lftln=leftsi;
            coun=coun+1;
   end
      break
     end
    end
end
disp(leftsi);
disp(lftln);   
widh=leftsi-lftln;
heig=toplen-tpln;
widt=widh/2;
disp(widt);
heit=heig/2;
with=lftln+widt;
heth=tpln+heit;
wth(l)=with;
hth(l)=heth;
 
disp(heit);
disp(widh);
disp(heig);
rectangle('Position',[lftln tpln widh heig],'EdgeColor','r');
disp(with);
disp(heth);
plot(with,heth, 'r*');
drawnow;
hold off
end

2.Track the image

clear data
disp('input video');
% Read in the video image samplevideo.avi and display ccbr1
avi=aviread('MVI_1069.avi');
video = {avi.cdata};
for a = 1:length(video)
    imagesc(video{a});
    axis image off
    drawnow;
end
disp('output video');
% Call the tracking() function to track the moving target
tracking(video);

[Wesley]

@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.

Answer 1

[darova]

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)

Read about curvature to find inflection points: LINK

Inflection point is a point where curvature changes its sign

[Wesley]

But if these discrete points are not obvious, how can we find the extreme points or inflection points?

[Image Analyst]

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.

Answer 2

[Image Analyst]

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]

I can process it in a single image, but the shape of the object in each frame of the video is changing, and I cannot process it in combination with the video.

[Wesley]

Is there another way to write a loop statement to save the processed pictures of each picture, and then make these pictures into a video?

[Image Analyst]

OK, so the shape changes but is the thing you want to record the location of there in every shape? Post a few shapes and indicate the point(s) that you want to find.

Sure you can write a video from images or figures or axes. I'm attaching several demos that make videos.

[Wesley]

I see. Thank you very much for your kind help.