Partial scan
The example below shows an ILT CCD in different partial scan modes. The charge from all of the pixels is moved into the vertical shift registers. The charge from the pixels that are not needed are dumped and excluded from the horizontal (readout) shift register.
The required pixels are read out as normal. As time is required for dumping off unwanted pixels, the frame rate increases are not quite linear to the reduction of the image height or number of sensor lines.
The effect visualized.