How to get the Mat object from the Byte[] in openCV android?

Question

I am working with OpenCV library in Android. I have a class which implements PictureCallBack.

The override method onPictureTaken() is as g

Answer 1

opencv has a neat way to writing Mats to files - it can generate different formats based on the file extension provided. Here is a minimal example:

    public void writeImageToFile(Mat image, String filename) {

    File root = Environment.getExternalStorageDirectory();
    File file = new File(root, filename);

    Highgui.imwrite(file.getAbsolutePath(), image);

    if (DEBUG)
        Log.d(TAG,
                "writing: " + file.getAbsolutePath() + " (" + image.width()
                        + ", " + image.height() + ")");
}

if red and blue is swapped then it sounds like your byte data from onPictureTaken() is in BGRA format. You can swap it to RGBA using:

Imgproc.cvtColor(bgrImg, rgbImg, Imgproc.COLOR_BGR2RGB);

the format is actually device specific - on one device I had it comes through as YUV.

Answer 2

You can use the imdecode method which comes as part of opencv (this is for emgucv but it should have a similar operation on other versions of opencv, syntax might just be different)

Example:

byte [] imageArray
Mat dest

CvInvoke.Imdecode(imageArray, ImreadModes.Unchanged, dest)

Answer 3

For me, the next works fine for me:

Java side:

    Bitmap bitmap = mTextureView.getBitmap(mWidth, mHeight);
    int[] argb = new int[mWidth * mHeight];
    // get ARGB pixels and then proccess it with 8UC4 OpenCV convertion
    bitmap.getPixels(argb, 0, mWidth, 0, 0, mWidth, mHeight);
    // native method (NDK or CMake)
    processFrame8UC4(argb, mWidth, mHeight);

OpenCV side (NDK):

JNIEXPORT jint JNICALL com_native_detector_Utils_processFrame8UC4
    (JNIEnv *env, jobject object, jint width, jint height, jintArray frame) {

    jint *pFrameData = env->GetIntArrayElements(frame, 0);
    // it is the line:
    Mat mFrame = Mat(height,width,CV_8UC4,pFrameData).clone();
    // your code..
    env->ReleaseIntArrayElements(frame, pFrameData, 0);

}

Answer 4

The best and easiest way is like this:

byte[] bytes = FileUtils.readFileToByteArray(new File("aaa.jpg"));
Mat mat = Imgcodecs.imdecode(new MatOfByte(bytes), Imgcodecs.CV_LOAD_IMAGE_UNCHANGED);

Answer 5

You have to specify width and height of the image/Mat and channels depth.

Mat mat = new Mat(width, height, CvType.CV_8UC3);
mat.put(0, 0, data);

Make sure you are using correct type of Mat. Maybe your data is not in 3 bytes RGB format and you should use another type e.g. CvType.CV_8UC1.
Good luck!