OpenCV Error: Null array pointer Java

Question

I am runing web-cam, trying to detect object in real time and I have this code running. It gives me error at video.main(video.java:92) - CvRect sq = cvBoundingRect(ptr, 0); But I am checking if(ptr != null) . I don't understand why.

CvMemStorage storage = CvMemStorage.create();
CvSeq contours = new CvContour(null);          
noOfContors = cvFindContours(imgbin, storage, contours, Loader.sizeof(CvContour.class), CV_RETR_CCOMP, CV_CHAIN_APPROX_NONE, new CvPoint(0,0));


 for (ptr = contours;  ptr != null; ptr = ptr.h_next()) {     
    if(ptr != null){
         CvRect sq = cvBoundingRect(ptr, 0);
         if(sq.height()*sq.width() > minAreaa && sq.height()* sq.width() < maxAreaa){
            p1.x(sq.x());
            p2.x(sq.x()+sq.width());
            p1.y(sq.y());
            p2.y(sq.y()+sq.height());
            cvRectangle(img1, p1, p2, CV_RGB(255, 0, 0), 2, 8, 0);
        } 
    }
}

In command window:

 OpenCV Error: Null pointer (NULL array pointer is passed) in unknown function, file ..\..\..\src\opencv\modules\core\src\array.cpp, line 2382
Exception in thread "main" java.lang.RuntimeException: ..\..\..\src\opencv\modules\core\src\array.cpp:2382: error: (-27) NULL array pointer is passed

    at com.googlecode.javacv.cpp.opencv_imgproc.cvBoundingRect(Native Method)
    at video.main(video.java:92)

Error mentions NULL array pointer.

PM 77-1
– PM 77-1

2013-12-29 23:41:15 +00:00
Commented Dec 29, 2013 at 23:41 — PM 77-1
– PM 77-1, Commented Dec 29, 2013 at 23:41

Arnas Ivanavičius · Accepted Answer · 2017-02-24 09:19:33Z

2

Solved the problem by adding an additional condition in for loop, but still don't know if it's a proper way to handle it:

CvSeq contours1 = new CvContour(null);
for (ptr = contours;  ptr != null && cvFindContours(imgbin, storage, contours1, Loader.sizeof(CvContour.class), CV_RETR_CCOMP, CV_CHAIN_APPROX_NONE, new CvPoint(0,0)) != 0; ptr = ptr.h_next()){ .....

}

edited Feb 24, 2017 at 9:19

answered Dec 30, 2013 at 0:59

Arnas Ivanavičius

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Comments

Rick Smith · Accepted Answer · 2015-08-25 16:11:10Z

0

Use the following instead:

 for (ptr = contours; ptr != null && !ptr.isNull(); ptr = ptr.h_next()) {

the !ptr.isNull() fixes the null pointer error.

edited Aug 25, 2015 at 16:11

Rick Smith

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answered Aug 25, 2015 at 16:07

Robert Truitt

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