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。

 1 //将bitmap转化为数组，保存到pixels中
 2 Bitmap mOriginalBmp = BitmapFactory.decodeResource(getResources(), R.drawable.test);
 3 int w = mOriginalBmp.getWidth();
 4 int h = mOriginalBmp.getHeight();
 5 int[] pixels = new int[w * h];
 6 mOriginalBmp.getPixels(pixels, 0, w, 0, 0, w, h);
 7  
 8 //调用Native方法获得处理过后的数组，转化为bitmap
 9 int[] resultInt = ImageProc.grayPoc(pixels, w, h);
10 Bitmap mBuildedBmp = Bitmap.createBitmap(resultInt,w, h,mOriginalBmp.getConfig());
11 mImageView.setImageBitmap(mBuildedBmp);
12  
13 //native方法定义
14 public static native int[] grayPoc(int[] pixels,int w,int h);
15  
16 //native的实现，将图片转化为灰度图
17 JNIEXPORT jintArray JNICALL Java_com_dengxy_opencvtest_ImageProc_grayPoc(
18             JNIEnv * env, jclass obj, jintArray buf, int w, int h) {
19         LOGD("Java_com_dengxy_opencvtest_ImageProc_grayPoc:start");
20         jint *cbuf;
21         cbuf = env->GetIntArrayElements(buf, JNI_FALSE);
22  
23         if (cbuf == NULL) {
24  
25             return 0;
26  
27         }
28         Mat imgData(h, w, CV_8UC4, (unsigned char *) cbuf);
29         uchar* ptr = imgData.ptr(0);
30  
31         for (int i = 0; i < w * h; i++) {
32  
33             int grayScale = (int) (ptr[4 * i + 2] * 0.299 + ptr[4 * i + 1] * 0.587 +
34  
35             ptr[4 * i + 0] * 0.114);
36  
37             ptr[4 * i + 1] = grayScale;
38  
39             ptr[4 * i + 2] = grayScale;
40  
41             ptr[4 * i + 0] = grayScale;
42  
43         }
44         int size = w * h;
45         jintArray result = env->NewIntArray(size);
46         env->SetIntArrayRegion(result, 0, size, cbuf);
47         env->ReleaseIntArrayElements(buf, cbuf, 0);
48         LOGD("Java_com_dengxy_opencvtest_ImageProc_grayPoc:end");
49         return result;
50     }

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。

 1 Bitmap mBuildedBmp = BitmapFactory.decodeResource(getResources(), R.drawable.test);
 2 ImageProc.getSobel(mBuildedBmp);
 3 mImageView.setImageBitmap(mBuildedBmp);
 4  
 5 //java接口函数
 6 private static native int getSobel(Bitmap in,Bitmap out);
 7  
 8 //对应的C++文件需要引入头文件 bitmap.h
 9 #include <android/bitmap.h>
10  
11  //对应C++函数
12 JNIEXPORT void JNICALL Java_com_dengxy_opencvtest_ImageProc_getSobel(
13         JNIEnv * env, jclass obj, jobject bmpIn) {
14     AndroidBitmapInfo inBmpInfo;
15     void* inPixelsAddress;
16     int ret;
17     if ((ret = AndroidBitmap_getInfo(env, bmpIn, &inBmpInfo)) < 0) {
18         LOGD("AndroidBitmap_getInfo() failed ! error=%d", ret);
19         return;
20     }
21     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);
22     if ((ret = AndroidBitmap_lockPixels(env, bmpIn, &inPixelsAddress)) < 0) {
23         LOGE("AndroidBitmap_lockPixels() failed ! error=%d", ret);
24     }
25     Mat inMat(inBmpInfo.height, inBmpInfo.width,
26             CV_8UC4, inPixelsAddress);
27     Sobel(inMat, inMat, inMat.depth(), 1, 1);
28     AndroidBitmap_unlockPixels(env, bmpIn);
29     LOGI("Return !! ");
30     return;
31  
32 }

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 -

 1 //Java层代码
 2         Bitmap oldBmp mBuildedBmp = BitmapFactory.decodeResource(getResources(), R.drawable.test);
 3         Mat bmpMat = new Mat();
 4         Utils.bitmapToMat(mBuildedBmp, bmpMat);
 5         long resultAddress = -1;
 6         resultAddress = ImageProc.getLaplacian(bmpMat.getNativeObjAddr());
 7         Log.d(TAG, "doLaplacian:resultAddress="+resultAddress);        
 8         if(resultAddress<0){
 9             return ;
10         }
11         Mat resultLaplacianMat = new Mat(resultAddress);
12         Utils.matToBitmap(resultLaplacianMat, mBuildedBmp);
13         mImageView.setImageBitmap(mBuildedBmp);
14  
15         //jni接口
16         public static native long getLaplacian(long bitmap);
17  
18         //c++实现
19 JNIEXPORT jlong JNICALL Java_com_dengxy_opencvtest_ImageProc_getLaplacian
20       (JNIEnv * env, jclass obj, jlong bmAddress){
21         LOGD("Java_com_dengxy_opencvtest_ImageProc_getLaplacian:start");
22         Mat *bitmpaMat = (Mat*) bmAddress;
23         if (NULL == bitmpaMat) {
24             LOGD("Java_com_dengxy_opencvtest_ImageProc_getLaplacian:the bitmpaMat is Null");
25             return -1;
26         }
27         Laplacian(*bitmpaMat,*bitmpaMat,bitmpaMat->depth());
28         jlong resultAddress = (jlong)bitmpaMat;
29         LOGD("Java_com_dengxy_opencvtest_ImageProc_getLaplacian:end");
30         return resultAddress;
31     }

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