OpenCV4Android 特征点提取演示

目标：

- 定义Native method 接口

- Bitmap 和 opencv Mat 之间的转换

- 通过org.opencv.core.Mat.getNativeObjAddr()把地址传递给底层的C++代码处理，然后更新对应地址的对象

关键代码：

Android中的事件处理：

    btn_feature_detect.setOnClickListener(new Button.OnClickListener() {

            @Override
            public void onClick(View v) {
                int width = bitmap.getWidth();
                int height = bitmap.getHeight();
                Mat mRgba = new Mat(height, width, CvType.CV_8U, new Scalar(4));
                Mat mGray = new Mat(height, width, CvType.CV_8U, new Scalar(4));
                Mat output = new Mat();

                Utils.bitmapToMat(bitmap, mRgba);

                // do sth
                // Converts an image from one color space to another.
                Imgproc.cvtColor(mRgba, mGray, Imgproc.COLOR_RGB2GRAY, 4);

                NativeUtil.detectFeatures(mGray.getNativeObjAddr(), mRgba.getNativeObjAddr(), output.getNativeObjAddr());

                // Then convert the processed Mat to Bitmap
                Bitmap resultBitmap = Bitmap.createBitmap(output.cols(),
                        output.rows(), Bitmap.Config.ARGB_8888);

                Utils.matToBitmap(output, resultBitmap);

                imageFeatureView.setImageBitmap(resultBitmap);
            }
        });

C++中利用opencv的处理：

JNIEXPORT void JNICALL Java_com_example_test_NativeUtil_detectFeatures(
        JNIEnv *env, jclass thiz, jlong mGrayAddr, jlong mRgbaAddr, jlong mOutputAddr) {
    Mat* pMatGr=(Mat*)mGrayAddr;
    Mat* pMatRgb=(Mat*)mRgbaAddr;
    Mat* pMatDesc=(Mat*)mOutputAddr;
    vector<KeyPoint> v;

    //OrbFeatureDetector detector(50);
    OrbFeatureDetector detector;
    OrbDescriptorExtractor extractor;
    detector.detect(*pMatGr, v);
    drawKeypoints(*pMatGr, v, *pMatDesc);
}

运行效果：

点击按钮后，提取该图片的features:

1.opencv ORB

2.Drawing Function of Keypoints and Matches

3.OpenCV Tutorial 2: Mixed Processing

4.Feature Description

5.Feature Detection and Description