With many CCD and CMOS chips, only a certain portion of the surface is sensitive to light. The rest of the surface can be taken up by readout electronics. For example, with interline transfer CCD chips, every second row is masked with a opaque layer. These masked rows are used to read out the illuminated pixels. Thanks to this design, the readout is very fast. These chips are therefore built into video and television cameras. Due to the resulting high number of units, interline transfer chips are particularly inexpensive.
With the help of microlenses, the lower sensitivity to light is compensated by the readout electronics. The surface is covered with tiny microscopic lenses that direct all the incoming light to the light-sensitive pixels.