A method and corresponding apparatus for monitoring breathing computes a calibration signal from a first sequence of images of a users chest to produce a calibration model.. The calibration signal is representative of movement of the users chest during a first time period during which the user is using an incentive spirometer a commercially-available (IS). The first sequence of images corresponds to the first time period. A method and corresponding apparatus employ the calibration model to produce a breathing information estimate about the users breathing from a second sequence of images of the users chest corresponding to a second time period during which the user is not using the a commercially-available IS. Example applications for the method and corresponding apparatus include vital sign applications for personalized healthcare through use of a smartphone.
