CCDs are always ready line-by-line, while some CMOS (global shutter) read all lines at the same time. However, in CCDs the image charges are physically shifted

CCDs are always ready line-by-line, while some CMOS (global shutter) read all lines at the same time. However, in CCDs the image charges are physically shifted downwards which causes streaking instead of a rolling shutter effect. There are (very expensive) frame-transfer CCDs which have a second readout sensor that is not light sensitive. This allows quickly shifting the image into this sensor, significantly reducing streaking.