In many color systems, all hope of controlled results vanishes at the scanner. It may be surprising to realize that there is still no one, universally accepted, method for designing a practical scanner's spectral sensitivities and related calibration method to provide colorimetrically accurate outputs for a device-independent result. Indeed, even the correct number of separate color channels to use in a practical scanner is an open question. At least 3 channels are needed for full-color, more are usually agreed to be a help. The various approaches are reviewed.