There are basically two types of image sensors CCD and CMOS used in video and still cameras.
A charge-coupled device (CCD) or CMOS (complementary metal oxide semiconductor) are image sensors incorporated in a computer chip used in most video cameras. They operate like a sophisticated light sensor similar to a human eye. CCD and CMOS sensors employ similar technology.
One example would of how the light to image transfer works is to compare it to a film camera. A video camera "sees" the world through lenses. In a film camera, the lenses serve to focus the light from a scene onto film coated with chemicals that have a reaction when exposed to light.
In this way, film in the camera records the scene in minute incremental shades from light to dark: It picks up greater amounts of light from brighter parts of the scene, and lower amounts of light from darker parts of the scene.
The lens in a video camera also serves to focus light, but instead of focusing it onto film, it diverts the light onto a small semiconductor image sensor. This sensor, a charge-coupled device (CCD), the CCD is acutely sensitive to light. The image is focused on a strip of light-sensitive diodes. Depending on the type of CCD, sensors can be made up of 300,000 to 500,000 tiny light sensitive diodes. called photo sites. These cells are arranged in horizontal rows and vertical columns. Each individual diode picks up light from light to dark and converts the"image" into electronic signals. The signals are then recorded on tape or hard drive, even SD cards, as moving images.
It is interesting to note that the photo sensor elements of a CCD and CMOS sensors respond to light in a fairly wide range of wavelengths. In other words, they can`t distinguish between colours. So a basic CCD sensor forms what is essentially a B&W (black and white) video image.