A colour input device such as a video camera has a similar set of sensors to cones. These respond to different wavelengths with different strengths. Essentially, a video camera is a digital device, based around an array of such sensors, and a clock that sweeps across them the same way that the electron gun in the back of a TV or computer display is scanned back and forth, and up and down, to refresh the light emission from the dots on the screen. So, for a single, still frame, a scan produces an array of reports of intensity, one element for each point in the back of the camera. For a system with 3 colour sensor types, you get an array of triples, values of intensity of light of each of the sensors at being a real. This is then converted into an analog signal for normal analog recording. Some devices are emerging where the values can be directly input to a computer rather than converted to analog, and then have to be converted to digital again by an expensive frame grabber or video card. Given the range of intensities the human eye can perceive isn't huge, they are usually stored digitally in a small number of bits - most usually 8 per colour - hence a ``true'' colour display has 24 bits, 8 bits each for R, G and B. RGB is the most commonly used computing colour model. CMY is just  - [RGB], and vice, versa. [0,0,0] is black, and [255,255,255] is white.