c - Write Portion of an Image to File -

while can write whole image file with

cvsaveimage("image.png", img); 

how can write given rectangle image i'm working on file?

there's mat constructor:

mat(const mat& m, const rect& roi); 

so use it!

or if use c (not c++) interface have set roi (region of interest):

http://nashruddin.com/opencv_region_of_interest_(roi)/

your code should this:

cvsetimageroi(img, rect);//rect roi cvsaveimage("image.png", img); 

if want work again full image have reset roi:

cvresetimageroi( iplimage* img )