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