<P> In computing, an image scanner is a device that optically scans images (printed text, handwriting, or an object) and converts it to a digital image which is transferred to a computer . Among other formats, flat, drum and film scanners exist, and most of them support RGB color . They can be considered the successors of early telephotography input devices, which were able to send consecutive scan lines as analog amplitude modulation signals through standard telephonic lines to appropriate receivers; such systems were in use in press since the 1920s to the mid-1990s . Color telephotographs were sent as three separated RGB filtered images consecutively . </P> <P> Currently available scanners typically use charge - coupled device (CCD) or contact image sensor (CIS) as the image sensor, whereas older drum scanners use a photomultiplier tube as the image sensor . Early color film scanners used a halogen lamp and a three - color filter wheel, so three exposures were needed to scan a single color image . Due to heating problems, the worst of them being the potential destruction of the scanned film, this technology was later replaced by non-heating light sources such as color LEDs . </P> <P> A color in the RGB color model is described by indicating how much of each of the red, green, and blue is included . The color is expressed as an RGB triplet (r, g, b), each component of which can vary from zero to a defined maximum value . If all the components are at zero the result is black; if all are at maximum, the result is the brightest representable white . </P> <P> These ranges may be quantified in several different ways: </P>

Red + blue + green = what color
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