direction of flow lines in an image

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Abhishek Saini
Abhishek Saini 2021-10-12
评论： yanqi liu 2021-10-12
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.

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yanqi liu
yanqi liu 2021-10-12
Ran in:
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));
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Abhishek Saini
Abhishek Saini 2021-10-12
thank you very much for a great answer. Are these things in the book. Is there English version of the book available?
yanqi liu
yanqi liu 2021-10-12
sir，thankyou
sorry，the book has not English version
but，we can also discuss

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yanqi liu
yanqi liu 2021-10-12
Ran in:
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');
  2 个评论
Abhishek Saini
Abhishek Saini 2021-10-12
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

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