direction of flow lines in an image

Hi,

I have a 2D image or image data. I want to find the average direction of flow lines with respect to horizontal. how can i do that.

Attached is the iamge I generated by using

imgradient

red lines I draw to show the approximate flow of lines in the image and \theta is the average angle , which I want to determine.

Answer 1

[yanqi liu]

sir，please check the follow code to get some information

for more information,you can read the book 《计算机视觉与深度学习实战》，Thank you！

clc; clear all; close all;
im = imread('https://ww2.mathworks.cn/matlabcentral/answers/uploaded_files/764756/untitled.jpg');
jm = rgb2lab(im);
s = mat2gray(jm(:,:,2));
bw = im2bw(s);
bw = bwareafilt(bw,1);
bw2 = imopen(bw, strel('line', 19, 0));
bw(bw2) = 0;
bw = bwareafilt(bw,1);

[H,T,R] = hough(bw);
P  = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));
lines = houghlines(bw,T,R,P,'FillGap',5,'MinLength',7);
max_len = 0;
line_r = [];
for k = 1:length(lines)
   xy = [lines(k).point1; lines(k).point2];
   % Determine the endpoints of the longest line segment
   len = norm(lines(k).point1 - lines(k).point2);
   if ( len > max_len)
      max_len = len;
      xy_long = xy;
      line_r = lines(k);
   end
end

figure; imshow(im); hold on;
plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','cyan');
title(sprintf('theta=%.1f°', 90-line_r.theta));

[Abhishek Saini]

I think the book is in chinese language. I Cannot understand it.

[yanqi liu]

sir，use vector to compute get

angle =

24.8756

>>

[Abhishek Saini]

Thanks for the response. Appreciate your quick reply.

I think the book is in chinese language. I Cannot understand it.

Also, I should rephrase my question. I inserted the lines in the image for demostration only. The original image is attached. I want to find the flow orientation of this image. As you can see the red lines are flowing from ottm left to top right at particular orientation. I want to measure the angle w..r.t. horizontal or vertical.

[yanqi liu]

clc; clear all; close all;
im = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/764931/image.jpeg');
jm = rgb2hsv(im);
s = mat2gray(jm(:,:,2));
bw = im2bw(s, 0.6);
bw = bwareaopen(bw, 100);
figure; imshow(bw, []);

bw = bwareafilt(bw, 20);
[L,num] = bwlabel(bw);
stats = regionprops(L, 'Centroid', 'BoundingBox','Orientation');
figure; imshow(im, []);
for i = 1 : num
    hold on; rectangle('position', stats(i).BoundingBox, 'EdgeColor', 'g', 'LineWidth', 2)
    text(stats(i).Centroid(1),stats(i).Centroid(2), sprintf('%.2f', stats(i).Orientation), 'Color', 'k', 'FontSize', 15);
end

[Abhishek Saini]

thank you very much for a great answer. Are these things in the book. Is there English version of the book available?

[yanqi liu]

sir，thankyou

sorry，the book has not English version

but，we can also discuss

Answer 2

[yanqi liu]

sir，please check the follow code to get some information

for more information,you can read the book 《计算机视觉与深度学习实战》，Thank you！

clc; clear all; close all;
img = imread('cameraman.tif');
[Gx,Gy] = imgradientxy(img);
[Gmag,Gdir] = imgradient(Gx,Gy);

mk = zeros(16,16);
mk(8:9,:) = 1;
mk = logical(mk);
ms = mk;
% rotae theta
mk = imrotate(mk, 30);
mk = bwmorph(mk,'thin',inf);
% find direction 
res = imfilter(double(Gdir), double(mk), 'replicate');
res = res > max(res(:))*0.5;

figure; 
subplot(2, 2, 1); imshow(mat2gray(Gdir)); title('origin image');
subplot(2, 2, 2); imshow(mat2gray(ms)); title('h base filter');
subplot(2, 2, 3); imshow(mat2gray(mk)); title('theta filter');
subplot(2, 2, 4); imshow(mat2gray(res)); title('result');

[Abhishek Saini]

Thanks yanqi liu for the response. But I donot understand the concept behind this. Why did you use

mk = imrotate(mk, 30);

Whatis the work of theta filter? My question is to find the angle of flow lines with respect to (w.r.t.) horizintal or vertical.

If you rotate the original image, the final results are still same, but it should change w.r.t. image angular direction

[yanqi liu]

sorry，sir，i made a mistake