question about analyze particle inside the ROI

[shenqhann]

hello,  dear everyone ,  

I have a color image, and I wanna count the particles "only" inside a ROI that  I created by the "freehand line selection tool", first I add the ROI into the ROI manager and then setup the color threshold  and  analyze particle , but it still counted all range of my image, if anyone can teach how to do it?

 Best Regards