I am quite new to vision and OpenCV, so forgive me if this is a stupid question but I have got really confused.
My aim is to detect an object in an image and estimate its actual size. Assume for now I only want length and width, not depth. Lets say I can detect the object, find its size(length and width) in pixels and I have both the intrinsic and extrinsic parameters of the camera.
The documentation of camera calibration as I understand says that the intrinsic and extrinsic camera parameters can be used to transform from camera coordinate system to world coordinate system. So this should mean converting from pixel coordinates to real coordinates right? And so I should be able to use pixel size and these parameters to find the real size?
But, say the object is photographed at different depth (distance from camera), then its size would come out different using above method. So.....what does it mean transforming from camera to world coordinates?
Any kind of explanation/links/help would be highly appreciated.