具有NDK抓取功能的Android Studio中的OpenCV始终返回黑色蒙版

Question

I created an Android Studio project with NDK support and OpenCV native libraries using the steps in this example:

https://github.com/leadrien/opencv_native_androidstudio

With this example working fine, I'm trying to use grabCut algorithm. My app should show 3 images in the main Activity: the original image, the transformed image and the mask used. But actually the mask that is showing is all black and, for that, the processed image is like the original one.

My java code:

    private void processImage(){
    Bitmap srcBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.pastis);

    Bitmap bmp32 = srcBitmap.copy(Bitmap.Config.ARGB_8888, true);

    Mat imgToProcess = new Mat();
    Mat mask = new Mat();

    //utils from opencv library
    Utils.bitmapToMat(bmp32, imgToProcess);

    //NDK function
    salt(imgToProcess.getNativeObjAddr(), mask.getNativeObjAddr(), 2000);

    Bitmap bmp = Bitmap.createBitmap(imgToProcess.cols(), imgToProcess.rows(), Bitmap.Config.ARGB_8888);

    //utils from opencv library
    Utils.matToBitmap(imgToProcess, bmp);

    Bitmap bmpMask = Bitmap.createBitmap(mask.cols(), mask.rows(), Bitmap.Config.ARGB_8888);

    //utils from opencv library
    Utils.matToBitmap(mask, bmpMask);

    ImageView imageContainer = (ImageView) findViewById(R.id.resultImage);
    imageContainer.setImageBitmap(bmp);

    ImageView maskContainer = (ImageView) findViewById(R.id.maskImage);
    maskContainer.setImageBitmap(bmpMask);
}

And my NDK code is:

void JNICALL Java_com_ach_MainActivity_salt(JNIEnv *env, jobject instance, jlong matAddrGray, jlong mask, jint nbrElem) {
Mat &mGr = *(Mat *) matAddrGray;
Mat &maskR = *(Mat *) mask;

int r = mGr.rows;
int c = mGr.cols;

Mat bgdModel, fgdModel;

Rect rect = Rect(10, 10,c-10, r-10);

cvtColor(mGr , mGr , CV_RGBA2RGB);
maskR.create(mGr.size(), CV_8UC1);

grabCut(mGr, maskR, rect, bgdModel, fgdModel, 2, GC_INIT_WITH_RECT);

mGr.copyTo(mGr, maskR);
}

¿Why I'm getting always all-black mask?

Moreover, execute grabCut it taking about 50 seconds in my mobile (Samsung Galaxy S5) with an image resolution of 256 x 192 and only 2 steps. ¿Is this normal?¿How can I improve this?

Thanks in advance :)

Answer 1

I found the problem some time ago but I forgot to post the answer.

It seems that there was a problem with some bugs in opencv + ndk and I solved my problem not using the same bitmap at source and destination in copyTo function:

mGr.copyTo(mGr, maskR); --> PROBLEMS

mGr.copyTo(mGrDest, maskR); --> WORKING

And, just in case, since this problem I avoid the same for other functions with source-destination bitmaps like cvtColor , but I think there is not problem with that function.

I hope my solution works with your codes! :)