direction of flow lines in an image

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Abhishek Saini 2021-10-12

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https://ww2.mathworks.cn/matlabcentral/answers/1561776-direction-of-flow-lines-in-an-image

评论： yanqi liu 2021-10-12

采纳的回答： yanqi liu

untitled.jpg

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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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Answer 1

yanqi liu 2021-10-12

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https://ww2.mathworks.cn/matlabcentral/answers/1561776-direction-of-flow-lines-in-an-image#answer_806681

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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

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 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 2021-10-12

sir，thankyou

sorry，the book has not English version

but，we can also discuss

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Answer 2

yanqi liu 2021-10-12

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1561776-direction-of-flow-lines-in-an-image#answer_806631

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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');

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Abhishek Saini 2021-10-12

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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 2021-10-12

sorry，sir，i made a mistake

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