The image on the left shows the basic principles of a CCD cell in comparison with a CMOS cell.
The charge generated in a CCD cell by incident light is directly read out from each cell. This charges are moved step by step outside of the photoactive area. Outside they are analogue/digital converted and amplified, resp.
In the CMOS cell the incident light generates a photo current proportional to its intensity in each cell and decreases the reverse resistance of each photo diode. These reverse currents through the photodiodes (i.e. the generated charges) are processed.