I understand the basics of what a CCD sensor is, but I can't seem to find a good explanation of how CMOS sensors differ from them. What operates differently, and what are the advantages and disadvantages? I know that CMOS has a problem with rolling shutter, so presumably, CCD records the entire image in one instant, while CMOS -- somehow, and for some reason -- captures it from top to bottom over time, or vice verca. But some high-end cameras like Red Epic use CMOS sensors, and there must be a reason for that.