Detects multiple disks (coins) in an image using Hough Transform

HOUGHCIRCLES detects multiple disks (coins) in an image using Hough Transform.

Description

HOUGHCIRCLES detects multiple disks (coins) in an image using Hough Transform. The image contains separating, touching, or overlapping disks whose centers may be in or out of the image.

Syntax
  houghcircles(im, minR, maxR);
  houghcircles(im, minR, maxR, thresh);
  houghcircles(im, minR, maxR, thresh, delta);
  circles = houghcircles(im, minR, maxR);
  circles = houghcircles(im, minR, maxR, thresh);
  circles = houghcircles(im, minR, maxR, thresh, delta);

Inputs:
  - im: input image
  - minR: minimal radius in pixels
  - maxR: maximal radius in pixels
  - thresh (optional): the minimal ratio of the number of detected edge pixels to 0.9 times the calculated circle perimeter (0<thresh<=1, default: 0.33)
  - delta (optional): the maximal difference between two circles for them to be considered as the same one (default: 12); e.g., c1=(x1 y1 r1), c2=(x2 y2 r2), delta = |x1-x2|+|y1-y2|+|r1-r2|

Output
  - circles: n-by-4 array of n circles; each circle is represented by (x y r t), where (x y), r, and t are the center coordinate, radius, and ratio of the detected portion to the circle perimeter, respectively. If the output argument is not specified, the original image will be displayed with the detected circles superimposed on it.

• Required Products: Image Processing Toolbox
• MATLAB release: MATLAB 7.5 (R2007b)

[Sven]

Nice function. Code is well documented and clearly written.
One suggestion is to follow the example of the peaks() function: if no output argument is given, then create a figure and display the image. If it's used with an output argument, assume the user is embedding the function in their own code, and doesn't want a figure to come up automatically.

[Idillus]

Hi, nice function. I've made some changes that may be interesting. It wold be nice to change the threshold and sigma value for canny edge detection, so, I added a few lines to improve this, changing the location of the definition of the edgeimage

if nargin==3
    
    thresh = 0.33; % One third of the perimeter
    delta = 12; % Each element in (x y r) may deviate approx. 4 pixels
    edgeim = edge(im, 'canny', [0.15 0.2]);

elseif nargin==4

    if ((max(size(canny_th) == 2)) || (max(size(canny_th) == 1)))
        if max(size(canny_th) == 2)
            edgeim = edge(im, 'canny', [canny_th(1) canny_th(2)]);
        end
        if max(size(canny_th) == 1)
            edgeim = edge(im, 'canny', canny_th(1));
        end
    end
    delta = 12;
    
else (nargin==5)

    if ((max(size(canny_th) == 2)) || (max(size(canny_th) == 1)))
        if (max(size(canny_th) == 2))
            edgeim = edge(im, 'canny', [canny_th(1) canny_th(2)],sigma);
        end
        if (max(size(canny_th) == 1))
            edgeim = edge(im, 'canny', canny_th(1),sigma);
        end
    end
    delta = 12;
end

[Idillus]

Sorry, I've made ma mistake

if (nargin >=3 || nargin <= 6)
    
    if nargin==3
        thresh = 0.33; % One third of the perimeter
        delta = 12; % Each element in (x y r) may deviate approx. 4 pixels
        edgeim = edge(im, 'canny', [0.15 0.2]);
    end
    
    if nargin==4
        edgeim = edge(im, 'canny', [0.15 0.2]);
        delta = 12;
    end
    
    if (nargin==5)
        edgeim = edge(im, 'canny', canny_th);
        delta = 12;
    end
    
    if (nargin==6)
       edgeim = edge(im, 'canny', canny_th,sigma);
       delta=12;
    end
    if (nargin == 7)
         edgeim = edge(im, 'canny', canny_th,sigma);
    end
end

if minR<0 || maxR<0 || minR>maxR || thresh<0 || thresh>1 || delta<0 || canny_th <0 || canny_th >1
  disp('Input conditions: 0<minR, 0<maxR, minR<=maxR, 0<thresh<=1, 0<delta');
  return;
end

[Rezki Al Khairi]

i've try to make with GUI...
but i cannot place where the instrustion mace be placed...
can u help me pleasee...
i really need it..

[sanjay bhattacharya]

i used the houhcircles function. it says 'out of memory' for my test images; but it worked for very small binary images; please help

[Yuan-Liang Tang]

sanjay,
The most probable cause might be that you invoked the function using inappropriate parameters. The function allocate a 3D matrix of size [size(im,1)+maxR, size(im,2)+maxR, maxR-minR+1], where minR and maxR are the minimal and maximal radii of circles you want to detect, respectively. You may want to check if the size of your input image or the values of minR and maxR are really huge.

[TUYEN Nguyen Ba]

Thank you Prof. Yuan Liang Tang. This is really great!

[Venugopalakrishna]

Thank you very much.

[Nazatul Naquiah Ahba]

hi, i've ran this code and it works. i wonder which part of the code display as accumulation array? can you pls guide me how to create the accumulation array from this code in order to generate the output figure of hough transform accumulation array?

[Christoph]

 

[Sushma Bhandari]

im unable to detect the circles.what should be the minR and mixR,can anyone help me?

[Yuan-Liang Tang]

Sushma,
  minR and maxR are the minimal and maximal radii (in pixels), respectively, of the circles that you want to detect in your image. For the image I provided along with the program, I set minR=20 and maxR=40. If you still have problems, you may want to provide your image and I'll look into the problem.

Yuan-Liang Tang