In both cases, the digital images of the colored solutions were acquired using an HP Deskjet G4050 scanner and X Sane software [37], with the auto-correction functions switched off and with the brightness and contrast the same for all the images acquired. The images were acquired in format TIFF (Tagged image file format). The procedures were performed in a GNU/Linux environment with distribution Ubuntu 12.04 LTS. The digital resolution was maintained at 300 dpi and 16 bits, and the images were subsequently processed in order to convert them to analytical signals. The treatment of images employed Matlab R2014a software (Mathworks) in conjunction with an image-processing toolkit (Mathworks).