The efficiency of a laundry-washing process is typically assessed using reflection measurements. A spectrometer and an integrating sphere are used to obtain the reflection data. The similarities between this equipment and a commercially available flatbed scanner are examined, and the way a flatbed scanner can be used to obtain detergent efficiencies is described. A flatbed scanner can be viewed as a singular spectrometer capable of obtaining spectral information concentrated in three regions of the visible spectrum. These data are stored in image files as coordinates in the red-green-blue (RGB) space where colors are represented by mixture of red, green, and blue in an 8-bit scale, that is, in a range where the intensities of these colors vary from 0 to 255. Detergent efficiencies calculated with these devices are compared. Washing tests on linseed-oil-impregnated white polyester fabrics are performed using sodium dodecyl sulfate with mass concentrations ranging from 0.00 to 1.00%. The results demonstrate that a flatbed scanner is a valuable and economical alternative to calculate detergent efficiencies in a wide variety of circumstances. (Contains 2 tables and 4 figures.)