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### Opencv-Java append image to existing image

I am trying to add an image below an original image. Then the new image will overwrite the old one. This method is run multiple times.

public void appendImage(Mat matToAppend){
Mat newMat = new Mat();
if(orgMat.total()==0){ // if no image exists
orgMat = matToAppend;
Highgui.imwrite("test.tiff", orgMat);
}
else{
int width = 0;
if(matToAppend.width() > orgMat.width()) // selects the biggest width
width = matToAppend.width();
else
width = orgMat.width();
int height = orgMat.height()+matToAppend.height(); // total height is the two images added together
newMat = new Mat(new Size(width, height), orgMat.type(), new Scalar(255, 255, 255));

Mat orgTarget = newMat.submat(new Rect(new Point(0, 0), new Point(orgMat.width(), orgMat.height())));
orgMat.copyTo(orgTarget); //copy old image to upper area

Mat newTarget = newMat.submat(new Rect(new Point(0, orgMat.height()), new Point(matToAppend.width(), newMat.height())));
matToAppend.copyTo(newTarget); // copy new image to bottom area
Highgui.imwrite("test.tiff", newMat);
}
}


What happening is that only the first image is placed at the top whereas the images appended afterwards are not seen. Running this method 4 times will result in a final image with the height of all images, but only the first image is placed at top, and the rest of the final image is white.

Why aren't the other images showing?