Question

I'm trying to create an image depicting matches between keypoints in images generated from sift files, using the Features2d.drawMatches method from openCV java API. I can't seem to figure out what kind of argument the method will take as an output parameter - I keep getting the following Assertion Error:

OpenCV(3.4.1) Error: Assertion failed (!outImage.empty()) in 
cv::drawKeypoints, file C:\build\master_winpack-bindings-win32-vc14- 
static\opencv\modules\features2d\src\draw.cpp, line 115
Exception in thread "main" CvException [org.opencv.core.CvException:  
cv::Exception: OpenCV(3.4.1) C:\build\master_winpack-bindings-win32-vc14- 
static\opencv\modules\features2d\src\draw.cpp:115: error: (-215) 
!outImage.empty() in function cv::drawKeypoints
]
    at org.opencv.features2d.Features2d.drawMatches_1(Native Method)
    at org.opencv.features2d.Features2d.drawMatches(Features2d.java:71)
    at com.company.GUI.ImagesView.matchPoints(ImagesView.java:94)
    at com.company.GUI.ImagesView.<init>(ImagesView.java:69)
    at com.company.Main.main(Main.java:17)

My code:

private void matchPoints() {
    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    MatOfKeyPoint matKey1 = new MatOfKeyPoint(keyPoints1);
    MatOfKeyPoint matKey2 = new MatOfKeyPoint(keyPoints2);
    MatOfDMatch matDMatch = new MatOfDMatch(matches);
    Mat output = new Mat();
    //output = new Mat(matKey1.rows(), matKey1.cols(), CvType.CV_8U, Scalar.all(0));
    if (!output.empty())
        System.out.println("not empty");
    else
        System.out.println("empty");
    Features2d.drawMatches(mat1, matKey1, mat2, matKey2, matDMatch, output);
    HighGui.imshow("Matches", output);
}

The exact same assertion error shows up whether or not I un-comment the commented line, despite the empty() check below returning different values for these two Mats. I'm at loss, help would be much appreciated.

Answer 1

我无法发表评论，因此我必须写一个答案：
我遇到了同样的问题，并以某种方式解决了它。这不是依赖性错误-我已经解决了它，而无需更改依赖性（或导入的库）。
如果正确计算出匹配项，则在调用此函数时不会发生此特定错误。
在我的代码中，错误是计算函数的调用。我试图用FastFeatureDetector调用此函数-但我在某处已经读到该检测器找不到任何匹配项。

尝试计算
ORB extractor = ORB.create(); extractor.compute(currentFrame, keyPoints, imgDescriptor);

尝试计算imgDescriptor时，不会发生任何错误；匹配后，您应该能够绘制匹配。
希望，我可以帮助您或其他遇到这种错误的人。

java opencv Features2d.drawMatches - Assertion failure or NullPointerException

1 个答案: