The CCD image sensor addresses the problem of noise, due to background charge generated by Compton scattering of gamma rays. A set of data channels for the ink colors of the system is generated, including at least one print-direction-independent data channel, and at least one pair of print-direction-dependent data channels. The pad casing is formed with an opening and it is filled with core material. A microwave detector coupled to the probe tip is configured to detect a near field microwave signal from the process fluid in response to the applied microwave signal. The generative models are based on appearances of multiple, possibly occluding objects in an image sequence.