free form image selection (preferably in c++)

Question

I am new to image manipulation. I have noticed that you can specify a rectangular region of interest and others like circles etc in image manipulation libraries like opencv. Basic paint programs like ms-paint incorporate free form selection but i cannot seem to find a function or tutorial on how to do free form image selection in opencv or other image processing libraries. Any ideas on how to achieve this? PS: My preferred language is c/c++.

Answer 1

One thing you can try:

If the selection can be represented as a sequence of 2d-vectors, you can think of it as a polygon. Allocate a new 1-channel image that will be your mask and fill it with 0. Then use

void cvFillPoly(CvArr* img, CvPoint** pts, int* npts, int contours, CvScalar color, int lineType=8, int shift=0)

documented on

http://opencv.willowgarage.com/documentation/drawing_functions.html

to draw a non-zero region on the mask image to represent the selected part of the image.