Line Detection via Standard Hough Transform

Detects lines in binary images via Standard Hough Transform.

Description

Function uses Standard Hough Transform to detect Lines in a binary image.
According to the Hough Transform, each pixel in image space corresponds to a line in Hough space and vise versa.This function uses
polar representation of lines i.e. x*cos(teta)+y*sin(teta)=p to detect
lines in binary image. upper left corner of image is the origin of polar coordinate system
Example :
[pdetect,tetadetect,Accumulator] = houghline(Imbinary,pstep,tetastep,thresh)

• Acknowledgements: This submission has inspired the following:; Parabola detection using Hough Transform
• Required Products: Image Processing Toolbox
• MATLAB release: MATLAB 7 (R14)

[Ravi Lakkundi]

We are trying to detect a line in an image, we applied this hough transform., Now we got the accumulator point, please tell us how will we remap that accumulator points back to image space.

[r zq]

It is a good work.

[Morten Engelsmann]

Easily understandable, readily useable

[Nicolas HUOT]

Hi, I discovered a bug in your file. It was unable to detect Positive sloped lines. I fixed it, tell me if I'm right on this:

function [pdetect,tetadetect,Accumulator] = houghline2(Imbinary,pstep,tetastep,thresh)
%HOUGHLINE - detects lines in a binary image using common computer vision operation known as the Hough Transform.
%
%Comments:
% Function uses Standard Hough Transform to detect Lines in a binary image.
% According to the Hough Transform, each pixel in image space
% corresponds to a line in Hough space and vise versa.This function uses
% polar representation of lines i.e. x*cos(teta)+y*sin(teta)=p to detect
% lines in binary image. upper left corner of image is the origin of polar coordinate
% system.
%
%Usage: [pdetect,tetadetect,Accumulator] = houghline(Imbinary,pstep,tetastep,thresh)
%
%Arguments:
% Imbinary - a binary image. image pixels that have value equal to 1 are
% interested pixels for HOUGHLINE function.
% pstep - interval for radius of lines in polar coordinates.
% tetastep - interval for angle of lines in polar coordinates.
% thresh - a threshold value that determines the minimum number of
% pixels that belong to a line in image space. threshold must
% be bigger than or equal to 3(default).
%
%Returns:
% pdetect - a vactor that contains radius of detected lines in
% polar coordinates system.
% tetadetect - a vector that contains angle of detcted lines in
% polar coordinates system.
% Accumulator - the accumulator array in Hough space.
%
%Originally Written by :
% Amin Sarafraz
% Photogrammetry & Computer Vision Devision
% Geomatics Department,Faculty of Engineering
% University of Tehran,Iran
% [e-mail]
%
%Bug fixed by:
% Nicolas HUOT
% Electrical Engineering and Computer Science Student
% UCLA (Los Angeles) and INPG (Grenoble)
% [e-mail]
%
%May 5,2004 - Original version
%November 24,2004 - Modified version,slightly faster and better performance.
%June 13, 2005 - Positive sloped lines possible (Nicolas HUOT)
                    

if nargin == 3
    thresh = 3;
elseif thresh < 3
    error('threshold must be bigger than or equal to 3')
    return;
end

p = -sqrt((size(Imbinary,1))^2+(size(Imbinary,2))^2):pstep:sqrt((size(Imbinary,1))^2+(size(Imbinary,2))^2);
teta = 0:tetastep:180-tetastep;

%Creating the accumulator:
Accumulator = zeros(length(p),length(teta)); %creating the Accumulator
[yIndex xIndex] = find(Imbinary); %extract the points from the image
for cnt = 1:size(xIndex) %looping on the list of points of the image
    Indteta = 0;
    for tetai = teta*pi/180 %looping on the list of possible teta (in radians)
        Indteta = Indteta+1;
        roi = xIndex(cnt)*cos(tetai)+yIndex(cnt)*sin(tetai); %ro computed
        if roi >= p(1) & roi <= p(end) %acceptable ro are filtered
            temp = abs(roi-p); %computing the distances between the roi and the list of acceptable values
            mintemp = min(temp); %picking the minimum of it
            Indp = find(temp == mintemp); %finding the indexes of this value
            Indp = Indp(1); %picking the first one
            Accumulator(Indp,Indteta) = Accumulator(Indp,Indteta)+1; %hop, increasing the coresponding point in the Accu
        end
    end %end loop tetai
end %end loop image points

% Finding local maxima in Accumulator
AccumulatorbinaryMax = imregionalmax(Accumulator); %creating the array of regional max
[Potential_p Potential_teta] = find(AccumulatorbinaryMax == 1); %picking up the maximums
Accumulatortemp = Accumulator - thresh; %leveling the accu by the threshold
pdetect = [];tetadetect = [];
for cnt = 1:length(Potential_p) %looping on the possible ro
    if Accumulatortemp(Potential_p(cnt),Potential_teta(cnt)) >= 0 %if the minimum threshold is reached
        pdetect = [pdetect;Potential_p(cnt)]; %append the new confirmed values
        tetadetect = [tetadetect;Potential_teta(cnt)];
    end
end

% Calculation of detected lines parameters(Radius & Angle).
pdetect = (pdetect - round(sqrt((size(Imbinary,1))^2+(size(Imbinary,2))^2)/pstep)) * pstep;
tetadetect = tetadetect *tetastep - tetastep;

[ali mot]

 

[akbar jafary]

 

[lamya durain]

I am not profesional in mat;ab yet ,but i want to thank you very much for your effort .

[zhao tong]

you are very good

[gaurav goyal]

gud

[jing zuo]

good

[reg zs]

You are very kindness

[X. King]

It's useful. Good job!

[Nong Minh Ngoc]

Thanks so much !

[HAMNETT CGU]

Thanks a lot!!

[Stijn Helsen]

Except for the bug (of determining half of the Hough space), the code can be made a lot faster by replacing the "find-method" for determining the p-index to calculation, for example : Indp = round(abs(roi+pmax)/pstep+1);
(where pmax is -p(1)) is a lot faster and as good.

[Stijn Helsen]

My previous comment was not completely correct. pmax shouldn't be p(1), but p(1)-pstep/2

[Jia Li]

 

[abbas emadi]

 

[Vijay Kumar]

 

[priya t]

 

[Junho Lee]

FOr Study

[bassam j]

Good program, can be simplified and it can be made faster. But very helpful..

[ale montes]

n/a

[kiran hidayat]

 

[Ricardo Cabral]

mintemp = min(temp);

Indp = find(temp == mintemp);

Indp = Indp(1);

could be replaced by

[mintemp, indp] = min(temp);
            

[collin]

How could we test the accuracy of the detection ? Could you suggest a way? My question applies also when using the standard hough functions.
Thank you

[Bob]

honestly, your program lacks of efficiency

[ines]

thank you for this code, but when i compile it i had some errors like :
line 45:elseif thresh < 3
              error('threshold must be bigger than or equal to 3')
              return;% error :this statement cannot be reached
           end

line 76 77 :
pdetect = [];tetadetect = [];
for cnt = 1:length(Potential_p)
    if Accumulatortemp(Potential_p(cnt),Potential_teta(cnt)) >= 0
%error: the variable 'pdetect' appears to change size on every lop iteration(same error for 'tetadetect')
        pdetect = [pdetect;Potential_p(cnt)];
        tetadetect = [tetadetect;Potential_teta(cnt)];
    end
end

[Gijs Huisman]

Unfortunately the bug posted on 13 Jun 2005 is still present and a real one, without this fix one will only find half the hough space. Further the improvement suggested on 30 Aug 2007 by Stijn Helsen does make a significant difference. I understand the original author might not be updating this anymore, it would be good if the community could take owner ship.

[Tarun Kothari]

 

[nishant]

 

[Pugazhendhi]

The code is very helpful to understand Hough transform. I need a help to find Square using Hough.