android - Error when adding two Mats in OpenCV, Java -

i writing opencv based image processing algorythm thresholding. algorythm written here in c++ language , rewriting in on java, android studio. in 1 line, have add 2 mat (opencv matrix) objects. in c++ res=img+res;, in java core.add(imgmat, res, res);. @ line error, cannot solve:

cvexception: /volumes/./././././././arithm.cpp:639: error: (-209) operation neither 'array op array' (where arrays have same size , same number of channels), nor 'array op scalar', nor 'scalar op array' in function void cv::arithm_op(...)

in code below see, both mat objects have same size , has same format (cvtype) too. again, how code looks in c++, can see in this question.

my code (java):

public bitmap thresholding(bitmap bitmap) {     mat imgmat = new mat();     utils.bitmaptomat(bitmap, imgmat);     imgmat.convertto(imgmat, cvtype.cv_32fc1, 1.0 / 255.0);      mat res = calcblockmeanvariance(imgmat, 21);     core.subtract(new matofdouble(1.0), res, res);     core.add(imgmat, res, res);      imgproc.threshold(res, res, 0.85, 1, imgproc.thresh_binary);     //imgproc.resize(res, res, new org.opencv.core.size(res.cols() / 2, res.rows() / 2));      res.convertto(res, cvtype.cv_8uc1, 255.0);     utils.mattobitmap(res, bitmap);      return bitmap; }  public mat calcblockmeanvariance (mat img, int blockside) {     mat = new mat();     mat resmat;     mat inpaintmask = new mat();     mat patch;     mat smallimg = new mat();     matofdouble mean = new matofdouble();     matofdouble stddev = new matofdouble();      img.convertto(i, cvtype.cv_32fc1);     resmat = mat.zeros(img.rows() / blockside, img.cols() / blockside, cvtype.cv_32fc1);      (int = 0; < img.rows() - blockside; += blockside)     {         (int j = 0; j < img.cols() - blockside; j += blockside)         {             patch = new mat(i,new rect(j,i, blockside, blockside));             core.meanstddev(patch, mean, stddev);              if (stddev.get(0,0)[0] > 0.01)                 resmat.put(i / blockside, j / blockside, mean.get(0,0)[0]);             else                 resmat.put(i / blockside, j / blockside, 0);         }     }      imgproc.resize(i, smallimg, resmat.size());     imgproc.threshold(resmat, inpaintmask, 0.02, 1.0, imgproc.thresh_binary);      mat inpainted = new mat();     imgproc.cvtcolor(smallimg, smallimg, imgproc.color_rgba2bgr);     smallimg.convertto(smallimg, cvtype.cv_8uc1, 255.0);      inpaintmask.convertto(inpaintmask, cvtype.cv_8uc1);     photo.inpaint(smallimg, inpaintmask, inpainted, 5, photo.inpaint_telea);      imgproc.resize(inpainted, resmat, img.size());     resmat.convertto(resmat, cvtype.cv_32fc1, 1.0 / 255.0);      return resmat; } 

thank in advance.

while imgmat , res have same size, have different number of channels: imgmat has 4 channels , res has 3 channels.

since can add 2 matrices if have same size , number of channels, can convert imgmat 3 channel image before calling add like:

imgproc.cvtcolor( imgmat, imgmat, imgproc.color_bgra2bgr);