Perform angle recognition on the objects in the following images
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clc
clear
A = imread('shipai.jpg');
A = rgb2gray(A);
BW = A<128;
% find angle of dominant line
[H,T,R] = hough(BW);
P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:))));
x = T(P(:,2)); y = R(P(:,1));
plot(x,y,'s','color','white');
lines = houghlines(BW,T,R,P,'FillGap',5,'MinLength',7);
imshow(A), hold on
max_len = 0;
for k = 1:length(lines)
xy = [lines(k).point1; lines(k).point2];
plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');
% Plot beginnings and ends of lines
plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');
% 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;
end
end
n = length(lines);
for i=1:n-1
k=(lines(i).theta-lines(i+1).theta);
if abs(k>=15)
jiaodu=k
return
end
end
That's the code I used originally. It has a good effect on the following image recognition
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/930364/image.png)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/930369/image.png)
Then you can get that the angle of two of the lines is 90
But for the following pictures, we can't recognize straight lines very well
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/930374/image.png)
I can't recognize the boundary straight line very well. The main reason is that my camera is not very good and the fabric is a little reflective. Is there any better way to deal with it? Thank you
4 Comments
Image Analyst
on 17 Mar 2022
I've spent about a third or half my working career over the past 30 years working on fabric image analysis. There are many papers published on it. See this link:
Accepted Answer
Simon Chan
on 17 Mar 2022
Edited: Simon Chan
on 17 Mar 2022
Do some filtering before searching for lines.
Need to increase the number of peaks to 20 for function houghpeaks otherwise it is not possible to detect the diagonal line.
clear; clc;
rawdata = imread('fabric.png');
A = rgb2gray(rawdata);
se = strel('square',3);
BW1 = imbothat(A,se); % Filtering
BW2 = bwareaopen(BW1>2,5); % Remove small objects
% find angle of dominant line
[H,T,R] = hough(BW2);
P = houghpeaks(H,20,'threshold',ceil(0.3*max(H(:)))); % Increase number of peaks = 20
x = T(P(:,2)); y = R(P(:,1));
plot(x,y,'s','color','white');
lines = houghlines(BW2,T,R,P,'FillGap',5,'MinLength',7);
imshow(A), hold on
max_len = 0;
for k = 1:length(lines)
xy = [lines(k).point1; lines(k).point2];
plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');
% Plot beginnings and ends of lines
plot(xy(1,1),xy(1,2),'x','LineWidth',2,'Color','yellow');
plot(xy(2,1),xy(2,2),'x','LineWidth',2,'Color','red');
% 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;
end
end
n = length(lines);
for i=1:n-1
k=(lines(i).theta-lines(i+1).theta);
if abs(k>=15)
jiaodu=k
return
end
end
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/930449/image.jpeg)
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