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welcome. what have you attempted?
would a proper photo editing program be a better idea? OpenCV is not a photo editing program.
okay. what’s the specific problem?
do you want documentation? do you want a course on image processing?
“need help” is not actionable. you need to show that you’ve done your homework.
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related:
Have a look at here
OutputArray can be the ROI of the original full image.
void cv::Mat::copyTo(OutputArray m, InputArray mask ) const