通过OpenCV在Android中使用本机功能

Question

我想使用本机函数使用OpenCV + Android。但是，我有点困惑如何使用位图作为参数以及如何返回已编辑位图（或Mat）的值。

因此，例如，我有一个本机函数：

#include <jni.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>


JNIEXPORT ??? JNICALL Java_com_my_package_name_and_javaclass_myFunction(JNIEnv* env, jobject javaThis, cv::Mat mat1){
    //here will be code to perform filtering, blurring, canny edge detection or similar things.
        //so I want to input a bitmap, edit it and send it back to the Android class.

return ???
    }

所以这里我使用cv ::
Mat作为参数。我知道这是错误的，但是我不确定应该是什么，以及对应的java类中应该是什么。应该是ByteArray吗？然后在上述本地函数中，参数将为jByteArray（或类似参数）？

对于返回对象，我应该放什么呢？应该是数组吗？

基本上，我要寻找的是Java类中的Mat（或位图），将其发送给本机函数进行编辑并返回经过良好编辑的位图。

Answer 1

这是Android的OpenCV教程代码。我记得我花了一段时间才了解JNI约定。只需先研究JNI代码

#include <jni.h>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <vector>

using namespace std;
using namespace cv;

extern "C" {
JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial3_Sample3View_FindFeatures(JNIEnv* env, jobject thiz, jint width, jint height, jbyteArray yuv, jintArray bgra)
{
    jbyte* _yuv  = env->GetByteArrayElements(yuv, 0);
    jint*  _bgra = env->GetIntArrayElements(bgra, 0);

    Mat myuv(height + height/2, width, CV_8UC1, (unsigned char *)_yuv);
    Mat mbgra(height, width, CV_8UC4, (unsigned char *)_bgra);
    Mat mgray(height, width, CV_8UC1, (unsigned char *)_yuv);

    //Please make attention about BGRA byte order
    //ARGB stored in java as int array becomes BGRA at native level
    cvtColor(myuv, mbgra, CV_YUV420sp2BGR, 4);

    vector<KeyPoint> v;

    FastFeatureDetector detector(50);
    detector.detect(mgray, v);
    for( size_t i = 0; i < v.size(); i++ )
        circle(mbgra, Point(v[i].pt.x, v[i].pt.y), 10, Scalar(0,0,255,255));

    env->ReleaseIntArrayElements(bgra, _bgra, 0);
    env->ReleaseByteArrayElements(yuv, _yuv, 0);
}
}

然后是Java代码

package org.opencv.samples.tutorial3;

import android.content.Context;
import android.graphics.Bitmap;

class Sample3View extends SampleViewBase {

    public Sample3View(Context context) {
        super(context);
    }

    @Override
    protected Bitmap processFrame(byte[] data) {
        int frameSize = getFrameWidth() * getFrameHeight();
        int[] rgba = new int[frameSize];

        FindFeatures(getFrameWidth(), getFrameHeight(), data, rgba);

        Bitmap bmp = Bitmap.createBitmap(getFrameWidth(), getFrameHeight(), Bitmap.Config.ARGB_8888);
        bmp.setPixels(rgba, 0/* offset */, getFrameWidth() /* stride */, 0, 0, getFrameWidth(), getFrameHeight());
        return bmp;
    }

    public native void FindFeatures(int width, int height, byte yuv[], int[] rgba);

    static {
        System.loadLibrary("native_sample");
    }
}