What am I doing wrong?

[ghost]

I am reading frames from a video. It displays on the canvas fine, but if I try to do anything with the mat it says its null.

This works to display on the canvasFrame.

OpenCVFrameConverter.ToMat openCVConverter = new OpenCVFrameConverter.ToMat();
Mat mat = openCVConverter.convert(frame);
canvasFrame.showImage(toBufferedImage(mat));

But this does not work to print out the width of the BufferedImage?

OpenCVFrameConverter.ToMat openCVConverter = new OpenCVFrameConverter.ToMat();
Mat mat = openCVConverter.convert(frame);
BufferedImage bf = toBufferedImage(mat);
System.out.println(bf.getWidth());

It returns:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.awt.image.BufferedImage.getWidth()" because "bf" is null

Am I doing something wrong?

[saudet]

What is toBufferedImage()?

[ghost]

public static BufferedImage toBufferedImage(Mat mat) {
        // Make sure that FrameConverters and JavaCV Frame are properly closed
        try (OpenCVFrameConverter.ToMat converter = new OpenCVFrameConverter.ToMat()) {
            try (Frame frame = converter.convert(mat)) {
                try (Java2DFrameConverter java2DConverter = new Java2DFrameConverter()) {
                    return java2DConverter.convert(frame);
                }
            }
        }
    }

This was just something i pulled to try and learn from. Its from the cookbook.

If I try to do something with the mat too i get the same.

int i = mat.rows();
System.out.println(i);

Weird it works for showing the frame but nothing else?

[saudet]

How do you check if frame.image is null or not?

[ghost]

works

  while ((frame = grabber.grab()) != null && canvasFrame.isVisible()) {
    OpenCVFrameConverter.ToMat openCVConverter = new OpenCVFrameConverter.ToMat();
    Mat mat = openCVConverter.convert(frame);
    canvasFrame.showImage(toBufferedImage(mat));
}

doesn't work

  while ((frame = grabber.grab()) != null && canvasFrame.isVisible()) {
    OpenCVFrameConverter.ToMat openCVConverter = new OpenCVFrameConverter.ToMat();
    Mat mat = openCVConverter.convert(frame);
    System.out.println(mat.rows);
}

and gives:

Exception in thread "main" java.lang.NullPointerException

[saudet]

How do you check if frame.image is null or not?

[ghost]

ahhh! That was the issue. Thanks very much.