watershed segmentation opencv xcode

Question

I am now learning a code from the opencv codebook (OpenCV 2 Computer Vision Application Programming Cookbook): Chapter 5, Segmenting images using watersheds, page 131.

Here is my main code:

#include "opencv2/opencv.hpp"
#include <string>

using namespace cv;
using namespace std;

class WatershedSegmenter {
    private:
    cv::Mat markers;
    public:
    void setMarkers(const cv::Mat& markerImage){
        markerImage.convertTo(markers, CV_32S);
    }

    cv::Mat process(const cv::Mat &image){
        cv::watershed(image,markers);
        return markers;
    }
};

int main ()
{
    cv::Mat image = cv::imread("/Users/yaozhongsong/Pictures/IMG_1648.JPG");

    // Eliminate noise and smaller objects
    cv::Mat fg;
    cv::erode(binary,fg,cv::Mat(),cv::Point(-1,-1),6);

    // Identify image pixels without objects
    cv::Mat bg;
    cv::dilate(binary,bg,cv::Mat(),cv::Point(-1,-1),6);
    cv::threshold(bg,bg,1,128,cv::THRESH_BINARY_INV);

    // Create markers image
    cv::Mat markers(binary.size(),CV_8U,cv::Scalar(0));
    markers= fg+bg;

    // Create watershed segmentation object
    WatershedSegmenter segmenter;
    // Set markers and process
    segmenter.setMarkers(markers);
    segmenter.process(image);

    imshow("a",image);
    std::cout<<".";
    cv::waitKey(0);
}

However, it doesn't work. How could I initialize a binary image? And how could I make this segmentation code work?

I am not very clear about this part of the book. Thanks in advance!

Hi, Is your problem with understanding the code? Also check the versions of the OpenCV used. I have also heard that there are some errors in that book, i haven't checked it. — Abid Rahman K
– Abid Rahman K, Commented Jul 11, 2012 at 16:42
I am using opencv 2.4.1...yea, I have some difficulty understanding this code... — Yaozhong
– Yaozhong, Commented Jul 11, 2012 at 18:35
You can check the link i have set in my answer. Not about how algorithm works, but how it function can be used. — Abid Rahman K
– Abid Rahman K, Commented Jul 11, 2012 at 18:36

Mark Fu · Accepted Answer · 2012-12-28 15:27:41Z

11

There's a couple of things that should be mentioned about your code:

Watershed expects the input and the output image to have the same size;
You probably want to get rid of the const parameters in the methods;
Notice that the result of watershed is actually markers and not image as your code suggests; About that, you need to grab the return of process()!

This is your code, with the fixes above:

// Usage: ./app input.jpg
#include "opencv2/opencv.hpp"
#include <string>

using namespace cv;
using namespace std;

class WatershedSegmenter{
private:
    cv::Mat markers;
public:
    void setMarkers(cv::Mat& markerImage)
    {
        markerImage.convertTo(markers, CV_32S);
    }

    cv::Mat process(cv::Mat &image)
    {
        cv::watershed(image, markers);
        markers.convertTo(markers,CV_8U);
        return markers;
    }
};


int main(int argc, char* argv[])
{
    cv::Mat image = cv::imread(argv[1]);
    cv::Mat binary;// = cv::imread(argv[2], 0);
    cv::cvtColor(image, binary, CV_BGR2GRAY);
    cv::threshold(binary, binary, 100, 255, THRESH_BINARY);

    imshow("originalimage", image);
    imshow("originalbinary", binary);

    // Eliminate noise and smaller objects
    cv::Mat fg;
    cv::erode(binary,fg,cv::Mat(),cv::Point(-1,-1),2);
    imshow("fg", fg);

    // Identify image pixels without objects
    cv::Mat bg;
    cv::dilate(binary,bg,cv::Mat(),cv::Point(-1,-1),3);
    cv::threshold(bg,bg,1, 128,cv::THRESH_BINARY_INV);
    imshow("bg", bg);

    // Create markers image
    cv::Mat markers(binary.size(),CV_8U,cv::Scalar(0));
    markers= fg+bg;
    imshow("markers", markers);

    // Create watershed segmentation object
    WatershedSegmenter segmenter;
    segmenter.setMarkers(markers);

    cv::Mat result = segmenter.process(image);
    result.convertTo(result,CV_8U);
    imshow("final_result", result);

    cv::waitKey(0);

    return 0;
}

I took the liberty of using Abid's input image for testing and this is what I got:

enter image description here

edited Dec 28, 2012 at 15:27

Mark Fu

3202 silver badges9 bronze badges

answered Jul 11, 2012 at 21:21

karlphillip

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8 Comments

Yaozhong Over a year ago

cool!it works!the size of original image and binary image should be the same. Thx!

karlphillip Over a year ago

This is from 2012. OpenCV API may have changed a bit since then. What problems are you having?

Daniel Over a year ago

@karlphillip I think he is referring to the fact that no segmentation has occurred?

karlphillip Over a year ago

@Daniel "Not working" is a poor definition of the problem. I can't help anyone without more technical information.

karlphillip Over a year ago

@Daniel Thanks for your comments. I would have never figured out all of that just from someone saying "It's not working". My first guess would be a compiler or a linker-related issue.

|

Community · Accepted Answer · 2017-05-23 12:01:18Z

4

Below is the simplified version of your code, and it works fine for me. Check it out :

#include "opencv2/objdetect/objdetect.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"

using namespace cv;
using namespace std;

int main ()
{
    Mat image = imread("sofwatershed.jpg");
    Mat binary = imread("sofwsthresh.png",0);

    // Eliminate noise and smaller objects
    Mat fg;
    erode(binary,fg,Mat(),Point(-1,-1),2);

    // Identify image pixels without objects
    Mat bg;
    dilate(binary,bg,Mat(),Point(-1,-1),3);
    threshold(bg,bg,1,128,THRESH_BINARY_INV);

// Create markers image
    Mat markers(binary.size(),CV_8U,Scalar(0));
    markers= fg+bg;

markers.convertTo(markers, CV_32S);
watershed(image,markers);

markers.convertTo(markers,CV_8U);
imshow("a",markers);
waitKey(0);
}

Below is my input image :

enter image description here

Below is my output image :

enter image description here

See the code explanation here : Simple watershed Sample in OpenCV

edited May 23, 2017 at 12:01

CommunityBot

11 silver badge

answered Jul 11, 2012 at 17:58

Abid Rahman K

52.8k31 gold badges149 silver badges158 bronze badges

6 Comments

Yaozhong Over a year ago

Thx! I have one question: what's the relationship between sofwatershed.jpg and sofwsthresh.png?

Abid Rahman K Over a year ago

OH. i am sorry. sofwatershed.png is the original image. sofwsthresh.png is the thresholded image. Actually i used Python. So i didn't want to binarize it again in C++. You can find those images in the link i have provided at end.

Yaozhong Over a year ago

I have a question, which image is your final segmentation image?is mat image?my image after the watershed function is the same as the original image...

Abid Rahman K Over a year ago

second image is the result. Actually i am not at all good in C++. I use Python only.

karlphillip Over a year ago

@AbidRahmanK +1 I upvoted your answer for the initiative, but that won't show the OP his mistakes. So I added an answer as well.

|

SlenderMuse · Accepted Answer · 2014-05-15 13:24:31Z

0

I had the same problem as you, following the exact same code sample of the cookbook (great book btw).

Just to place the matter I was coding under Visual Studio 2013 and OpenCV 2.4.8. After a lot of searching and no solutions I decided to change the IDE.

It's still Visual Studio BUT it's 2010!!!! And boom it works!

Becareful of how you configure Visual Studio with OpenCV. Here's a great tutorial for installation here

Good day to all

answered May 15, 2014 at 13:24

SlenderMuse

1

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