Image stitching: NullPointerException

问题

I have run this code. It seems to be that result.png is not generated as a result:

public class ImageStitching {

    public static void main(String[] args){
        MatVector images = new MatVector(2);
        images.put(0,cvLoadImage("sample1.png"));
        images.put(1,cvLoadImage("sample2.png"));

        IplImage result = new IplImage(null);
        int status = stitcher.stitch(images,result);

        if( status == stitcher.OK )
        {
            cvSaveImage("result.png", result);
        }

       result = cvLoadImage("result.png");

       final CanvasFrame canvas = new CanvasFrame("My Image", 1);

       // Request closing of the application when the image window is closed.
       canvas.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);

       // Show image on window.
       canvas.showImage(result);

      }
}

and the error is

Exception in thread "main" java.lang.NullPointerException
at com.googlecode.javacv.CanvasFrame.showImage(CanvasFrame.java:366)
    at com.googlecode.javacv.CanvasFrame.showImage(CanvasFrame.java:363)
    at ImageStitching.main(ImageStitching.java:50)

java:50 is canvas.showImage(result);

回答1:

Apparently, result is null when you call showImage.

The problem in your code is that you test if the status is OK (if ( status == stitcher.OK )), and then you try to load the file anyway. Your code should be something like:

if ( status != stitcher.OK )
{
    std::cout << "ERROR" << std::endl;
    return 1;
}

Then you would probably see that the problem comes from the stitching.

---

Moreover, you don't need to write result to a file before showing it.

来源：https://stackoverflow.com/questions/16624953/image-stitching-nullpointerexception