Jni中图片传递的3种方式（转）

java层的图片如何传递到c／c+层处理，处理完之后如何传回java层，下面总结了一下用到的三种方法。

1.将Bitmap转为int[]数组对象，将数组作为参数传递到C／C++层，处理完之后再以int[]数组返回。

//将bitmap转化为数组，保存到pixels中
Bitmap mOriginalBmp = BitmapFactory.decodeResource(getResources(), R.drawable.test);
int w = mOriginalBmp.getWidth();
int h = mOriginalBmp.getHeight();
int[] pixels = new int[w * h];
mOriginalBmp.getPixels(pixels, 0, w, 0, 0, w, h);
 
//调用Native方法获得处理过后的数组，转化为bitmap
int[] resultInt = ImageProc.grayPoc(pixels, w, h);
Bitmap mBuildedBmp = Bitmap.createBitmap(resultInt,w, h,mOriginalBmp.getConfig());
mImageView.setImageBitmap(mBuildedBmp);
 
//native方法定义
public static native int[] grayPoc(int[] pixels,int w,int h);
 
//native的实现，将图片转化为灰度图
JNIEXPORT jintArray JNICALL Java_com_dengxy_opencvtest_ImageProc_grayPoc(
            JNIEnv * env, jclass obj, jintArray buf, int w, int h) {
        LOGD("Java_com_dengxy_opencvtest_ImageProc_grayPoc:start");
        jint *cbuf;
        cbuf = env->GetIntArrayElements(buf, JNI_FALSE);
 
        if (cbuf == NULL) {
 
            return 0;
 
        }
        Mat imgData(h, w, CV_8UC4, (unsigned char *) cbuf);
        uchar* ptr = imgData.ptr(0);
 
        for (int i = 0; i < w * h; i++) {
 
            int grayScale = (int) (ptr[4 * i + 2] * 0.299 + ptr[4 * i + 1] * 0.587 +
 
            ptr[4 * i + 0] * 0.114);
 
            ptr[4 * i + 1] = grayScale;
 
            ptr[4 * i + 2] = grayScale;
 
            ptr[4 * i + 0] = grayScale;
 
        }
        int size = w * h;
        jintArray result = env->NewIntArray(size);
        env->SetIntArrayRegion(result, 0, size, cbuf);
        env->ReleaseIntArrayElements(buf, cbuf, 0);
        LOGD("Java_com_dengxy_opencvtest_ImageProc_grayPoc:end");
        return result;
    }

这种方法需要重复的拷贝，转化图片数据，空间和时间复杂度较高，效率较低。

2.直接将Bitmap对象传递到底层,C/C++获得Bitmap数据的指针，再转化为Mat，这种方法为底层直接操作bitmap的内存空间，操作前后会锁住该地址空间，完了java层刷新界面就可以了,
这里是一个Sobel边缘检测。用的时候发现要是内存空间有拷贝，操作的不是当前图片所在的内存空间的话，图片是改变不了的。

Bitmap mBuildedBmp = BitmapFactory.decodeResource(getResources(), R.drawable.test);
ImageProc.getSobel(mBuildedBmp);
mImageView.setImageBitmap(mBuildedBmp);
 
//java接口函数
private static native int getSobel(Bitmap in,Bitmap out);
 
//对应的C++文件需要引入头文件 bitmap.h
#include <android/bitmap.h>
 
 //对应C++函数
JNIEXPORT void JNICALL Java_com_dengxy_opencvtest_ImageProc_getSobel(
        JNIEnv * env, jclass obj, jobject bmpIn) {
    AndroidBitmapInfo inBmpInfo;
    void* inPixelsAddress;
    int ret;
    if ((ret = AndroidBitmap_getInfo(env, bmpIn, &inBmpInfo)) < 0) {
        LOGD("AndroidBitmap_getInfo() failed ! error=%d", ret);
        return;
    }
    LOGI("original image :: width is %d; height is %d; stride is %d; format is %d;flags is   %d,stride is %u", inBmpInfo.width, inBmpInfo.height, inBmpInfo.stride, inBmpInfo.format, inBmpInfo.flags, inBmpInfo.stride);
    if ((ret = AndroidBitmap_lockPixels(env, bmpIn, &inPixelsAddress)) < 0) {
        LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
    }
    Mat inMat(inBmpInfo.height, inBmpInfo.width,
            CV_8UC4, inPixelsAddress);
    Sobel(inMat, inMat, inMat.depth(), 1, 1);
    AndroidBitmap_unlockPixels(env, bmpIn);
    LOGI("Return !! ");
    return;
 
}

3.直接将Bitmap转化为Mat后，获取mat内存地址传到底层，处理后再返回内存地址到java层，根据地址加载Mat对象转化为bitmap。这种方法较上一种主要是内存空间有改变有可以，但是用的时候发现系统一GC回收图片，底层就出现了空指针，一看是底层MAT的析构函数没做非空判断，于是尝试着自己编译opencv4android，折腾了两天始终编译没通过，泪渀- o -

//Java层代码
        Bitmap oldBmp mBuildedBmp = BitmapFactory.decodeResource(getResources(), R.drawable.test);
        Mat bmpMat = new Mat();
        Utils.bitmapToMat(mBuildedBmp, bmpMat);
        long resultAddress = -1;
        resultAddress = ImageProc.getLaplacian(bmpMat.getNativeObjAddr());
        Log.d(TAG, "doLaplacian:resultAddress="+resultAddress);        
        if(resultAddress<0){
            return ;
        }
        Mat resultLaplacianMat = new Mat(resultAddress);
        Utils.matToBitmap(resultLaplacianMat, mBuildedBmp);
        mImageView.setImageBitmap(mBuildedBmp);
 
        //jni接口
        public static native long getLaplacian(long bitmap);
 
        //c++实现
JNIEXPORT jlong JNICALL Java_com_dengxy_opencvtest_ImageProc_getLaplacian
      (JNIEnv * env, jclass obj, jlong bmAddress){
        LOGD("Java_com_dengxy_opencvtest_ImageProc_getLaplacian:start");
        Mat *bitmpaMat = (Mat*) bmAddress;
        if (NULL == bitmpaMat) {
            LOGD("Java_com_dengxy_opencvtest_ImageProc_getLaplacian:the bitmpaMat is Null");
            return -1;
        }
        Laplacian(*bitmpaMat,*bitmpaMat,bitmpaMat->depth());
        jlong resultAddress = (jlong)bitmpaMat;
        LOGD("Java_com_dengxy_opencvtest_ImageProc_getLaplacian:end");
        return resultAddress;
    }

转自：http://www.apkbus.com/forum.php?mod=viewthread&tid=267283&_dsign=760031da