How to replace part of the image with another image ROI

Question

using opencv2.4.11 java API i am trying to truncate part of an image and then place it on another image.

the code posted below shows, the truncate Mat object is a truncated part of the img_1 posted below. and img_2 is the image that should host the truncated part of the "truncated" Mat object.

When i run the code, the result is the img_3, and i exepected to see img_2 overlapped with the "truncated" Mat object img_3.

please let me know how to achieve this properly.

static final String PATH5 = "c:.../images/CannyDest.jpg";
static final String PATH6 = "c:.../images/BlurredDest.jpg";

public static void main(String[] args) {
    ....
    ....
    ....

    Mat temp = Highgui.imread(PATH5);//img_1
    Mat trunctaed = temp.submat(new Rect(0, 0, 30, 30));
    Mat target = Highgui.imread(PATH6);//img_2
    trunctaed.copyTo(target);
    Highgui.imwrite(PATH6, trunctaed);//img_3
    //Highgui.imwrite(PATH6, target);// results in img_3
}

img_1

img_2

img_3

Answer 1

According to the opencv dos, The parameter of copyTop() is the target. and you're saving the trunctaed picture and should actually save target