Jni中圖片傳遞的3種方式（轉）

java層的圖片如何傳遞到c／c+層處理，處理完之后如何傳回java層，下面總結了一下用到的三種方法。

1.將Bitmap轉為int[]數組對象，將數組作為參數傳遞到C／C++層，處理完之后再以int[]數組返回。

//將bitmap轉化為數組，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);
 
//調用Native方法獲得處理過后的數組，轉化為bitmap
int[] resultInt = ImageProc.grayPoc(pixels, w, h);
Bitmap mBuildedBmp = Bitmap.createBitmap(resultInt,w, h,mOriginalBmp.getConfig());
mImageView.setImageBitmap(mBuildedBmp);
 
//native方法定義
public static native int[] grayPoc(int[] pixels,int w,int h);
 
//native的實現，將圖片轉化為灰度圖
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;
    }

這種方法需要重復的拷貝，轉化圖片數據，空間和時間復雜度較高，效率較低。

2.直接將Bitmap對象傳遞到底層,C/C++獲得Bitmap數據的指針，再轉化為Mat，這種方法為底層直接操作bitmap的內存空間，操作前后會鎖住該地址空間，完了java層刷新界面就可以了,
這里是一個Sobel邊緣檢測。用的時候發現要是內存空間有拷貝，操作的不是當前圖片所在的內存空間的話，圖片是改變不了的。

Bitmap mBuildedBmp = BitmapFactory.decodeResource(getResources(), R.drawable.test);
ImageProc.getSobel(mBuildedBmp);
mImageView.setImageBitmap(mBuildedBmp);
 
//java接口函數
private static native int getSobel(Bitmap in,Bitmap out);
 
//對應的C++文件需要引入頭文件 bitmap.h
#include <android/bitmap.h>
 
 //對應C++函數
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.直接將Bitmap轉化為Mat后，獲取mat內存地址傳到底層，處理后再返回內存地址到java層，根據地址加載Mat對象轉化為bitmap。這種方法較上一種主要是內存空間有改變有可以，但是用的時候發現系統一GC回收圖片，底層就出現了空指針，一看是底層MAT的析構函數沒做非空判斷，於是嘗試着自己編譯opencv4android，折騰了兩天始終編譯沒通過，淚渀- o -

//Java層代碼
        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++實現
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;
    }

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