CIS is a relatively new sensor technology which began to appear at the budget end of the flatbed scanner market in the late 1990s. CIS scanners employ dense banks of red, green and blue LEDs to produce white light and replace the mirrors and lenses of a CCD scanner with a single row of sensors placed extremely close to the source image. The result is a scanner that is thinner and lighter, more energy efficient and cheaper to manufacture than a traditional CCD-based device – but that is not, as yet, capable producing as good results.
The colour gamut of a CIS scanner is determined by the spectrum of each of the LEDs, rather than by the colour filters employed in the optical system of a CCD scanner. Since colour filter technology is more developed than LED spectrum technology, a CIS scanner will not provide as wide a colour gamut as a CCD scanner. However, the technology employed by its sensor mechanism is not the only factor that governs a scanner level of performance. The following are equally important aspects of a given unit’s specification:
- bit depth
- dynamic range