Documentation

houghlines

Extract line segments based on Hough transform

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Syntax

lines = houghlines(BW,theta,rho,peaks)
lines = houghlines(___,Name,Value,...)

Description

example

lines= houghlines(BW,theta,rho,peaks)extracts line segments in the imageBWassociated with particular bins in a Hough transform.thetaandrhoare vectors returned by functionhough.peaksis a matrix returned by thehoughpeaksfunction that contains the row and column coordinates of the Hough transform bins to use in searching for line segments. The return valuelinesis a structure array whose length equals the number of merged line segments found.

example

lines= houghlines(___,Name,Value,...)extracts line segments in the imageBW, where named parameters affect the operation.

Examples

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Open Live Script

Read image into workspace.

I = imread('circuit.tif');

Rotate the image.

rotI = imrotate(I,33,'crop');

Create a binary image.

BW = edge(rotI,'canny');

Create the Hough transform using the binary image.

[H,T,R] = hough(BW); imshow(H,[],'XData',T,'YData',R,...'InitialMagnification','fit'); xlabel('\theta'), ylabel('\rho'); axison, axisnormal, holdon;

Find peaks in the Hough transform of the image.

P = houghpeaks(H,5,'threshold',ceil(0.3*max(H(:)))); x = T(P(:,2)); y = R(P(:,1)); plot(x,y,'s','color','white');

Find lines and plot them.

lines = houghlines(BW,T,R,P,'FillGap',5,'MinLength',7); figure, imshow(rotI), holdonmax_len = 0;fork = 1:length(lines) xy = [lines(k).point1; lines(k).point2]; plot(xy(:,1),xy(:,2),'LineWidth',2,'Color','green');% Plot beginnings and ends of linesplot(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 segmentlen = norm(lines(k).point1 - lines(k).point2);if( len > max_len) max_len = len; xy_long = xy;endend

Highlight the longest line segment by coloring it cyan.

plot(xy_long(:,1),xy_long(:,2),'LineWidth',2,'Color','cyan');

Input Arguments

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Binary image, specified as a real, 2-D, nonsparse logical or numeric array.

Data Types:single|double|int8|int16|int32|int64|uint8|uint16|uint32|uint64|logical

Line rotation angle in radians, specified as a real, 2-D, nonsparse logical or numeric array.

Data Types:double

Distance from the coordinate origin, specified as a real, 2-D, nonsparse logical or numeric array. The coordinate origin is the top-left corner of the image (0,0).

Data Types:double

Row and column coordinates of Hough transform bins, specified as a real, nonsparse numeric array.

Data Types:double

Name-Value Pair Arguments

Specify optional comma-separated pairs ofName,Valuearguments.Nameis the argument name andValueis the corresponding value.Namemust appear inside single quotes (' '). You can specify several name and value pair arguments in any order asName1,Value1,...,NameN,ValueN.

Example:行= houghlines (BW T R P 'FillGap',5,'MinLength',7);

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Distance between two line segments associated with the same Hough transform bin, specified as a positive real scalar. When the distance between the line segments is less than the value specified, thehoughlinesfunction merges the line segments into a single line segment.

Data Types:double

Minimum line length, specified as a positive real scalar.houghlinesdiscards lines that are shorter than the value specified.

Data Types:double

Output Arguments

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Lines found, returned as a structure array whose length equals the number of merged line segments found. Each element of the structure array has these fields:

Field

Description

point1

Two element vector[X Y]指定的端点的坐标line segment

point2

Two element vector[X Y]指定的端点的坐标line segment

theta

Angle in degrees of the Hough transform bin

rho

rhoaxis position of the Hough transform bin

Extended Capabilities

See Also

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Introduced before R2006a

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