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Digital still cameras are cameras whose primary purpose is to capture photography in a digital format. Initially, a digital camera was characterized by the use of flash memory and USB or FireWire for storage and transfer of still photographs (though some early cameras used a serial port connection), and this is still the common meaning of the unadorned term. However, modern digital photography cameras have a video function, and a growing number of camcorders have a still photography function. In addition, some newer camcorders record video directly to flash memory and transfer over USB and FireWire. Among digital still cameras, most have a rear LCD for reviewing photographs. They are rated in megapixels; that is, the product of their maximum resolution dimensions in millions. The actual transfers to a host computer are commonly carried out using the USB mass storage device class (so that the camera appears as a drive) or using the Picture Transfer Protocol and its derivatives. All use either a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) sensor, i.e. chips comprised of a grid of phototransistors to sense the light intensities across the plane of focus of the camera lens. CMOS sensors are differentiated from CCDs proper in that it uses less power and a different kind of light sensing material, however the differences are highly technical and many manufacturers still consider the CMOS chip a charged coupled device. For our purposes, a chip sensor is a CCD.
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