Convert an open cv mat to an integer array

Question

I am trying to convert an open cv mat of type CV_8UC3 (RGB) to an integer array.

void copyMatToJIntArray(Mat m,jint* jia)
{

    Mat tempMat;
    cvtColor(m,tempMat,CV_BGRA2RGB);
    jint size = tempMat.rows*tempMat.cols* tempMat.elemSize();
    u_char * uchars = new u_char[size];  

    for(int r=0;r<tempMat.rows;r++)
    {
        for(int c=0;c<tempMat.cols;c++)
        {
            u_char r=*(tempMat.data+ r*tempMat.step + c);
            u_char g=*(tempMat.data+ r*tempMat.step + c+1);
            u_char b=*(tempMat.data+ r*tempMat.step + c+2);
            uchars[r*tempMat.step+c]=r;
            uchars[r*tempMat.step+c+1]=g;
            uchars[r*tempMat.step+c+2]=b;
        }
    }

    for (int i = 0; i < tempMat.rows*tempMat.cols; i++)
    {
        jia[i] = uchars[i];
    }
}

I pass this inteher array via JNI to android java where it is converted into an a bitmap

croppedImageBitmap.setPixels(BGRA, 0, width, 0, 0, width, height);
imageView1.setImageBitmap(croppedImageBitmap);

But when I view it on my android test phone, there is a blue tint over the image

Dmitrii Z. · Answer 1 · 2017-12-22T21:33:45.173

Try this

jintArray resultImage = env->NewIntArray(h.total());
jint *_data = new jint[h.total()];
for (int i = 0; i < h.total(); i++) {
    char b = h.data[h.channels() * i];
    char g = h.data[h.channels() * i + 1];
    char r = h.data[h.channels() * i + 2];
    char a = 255;
    _data[i] = (((jint) a << 24) & 0xFF000000) + (((jint) r << 16) & 0x00FF0000) +
               (((jint) g << 8) & 0x0000FF00) + ((jint) b & 0x000000FF);
}
env->SetIntArrayRegion(resultImage, 0, h.total(), _data);
delete[]_data;

And on your java side

int[] result = yourfunction();
Bitmap bitmap = Bitmap.createBitmap(result, yourimagewidth, yourimageheight, Bitmap.Config.ARGB_8888);

score 0 · Answer 2 · answered Dec 22 '17 at 19:48

I don't know Java but it is almost the same as opencv in c++, you can use my c++ version:

typedef std::vector<std::vector<int> > Matrix;

Matrix int_Im(3, std::vector<int>(m.cols*m.rows,0));
Matrix copyMatToJIntArray(Mat m,jint* jia)
{
   for(auto j=0, k = 0;j<m.rows;j++)
        for(auto i=0;i<m.cols;i++)
        {
            int_Im[k][0] = m.at<uchar>(j,i)[0];
            int_Im[k][1] = m.at<uchar>(j,i)[1];
            int_Im[k][2] = m.at<uchar>(j,i)[2];
            k++;
        }
  return int_Im;
}

arxakoulini · Answer 3 · 2017-12-28T18:56:40.413

Array data format should correspond to the Mat's type according to this table

    public static Mat arrayToMat(double[][] array,int height, int width, int matType)
    {
        Mat image = new Mat(height,width,matType);
        for (int i=0; i<height; i++)
        {
            for (int j=0; j<width; j++)
            {
                image.put(i,j,array[i][j]);
            }
        }
        return image;
    }

    public static double[][] matToArray(Mat frame)
    {
        double array[][] = new double[frame.height()][frame.width()];
        for (int i=0; i < frame.height(); i++)
        {
            for (int j=0; j < frame.width(); j++)
            {
                array[i][j] = frame.get(i,j)[0];
            }
        }
        return array;
    }

Convert an open cv mat to an integer array

3 Answers3