The role of colorants in the generation, storage, and output of digital still images

Abstract

Summary and Conclusions The role played by both dye and pigment colorants in thedigital still imaging process is of paramount importance.The initial input is the use of dyes and pigments to producethe RGB Bayer pattern on image-sensor colour filter arrayelements. The conversion of the initially captured greyscaleimage to a full-colour image is only made possible, onalmost all current digital cameras, by the presence of theRGB Bayer filter array. The role of cyanine, phthalocyanine,and azo-metal complex dyes as the recording layer for CD-R,DVD-R, and Blu-ray optical data storage systems cannot beunderestimated in the continued drive for high-capacitydigital image storage systems, and it is to be hoped thatspecific dyes will also play a part in future three-dimen-sional optical data storage systems when they eventuallyreach commercial fruition. Although many amateur pho-tographers still tend to rely on image-processing outlets toobtain hard-copy reflective prints from their digital imagefiles, and hence receive predominantly laser-optimal silverhalide images, many, including a high percentage ofprofessional photographers, prefer to use photorealisticnon-impact printing technologies. The most popular sys-tems include inkjet, thermal dye transfer, and electropho-tography. Each of these systems uses either dyes orpigments, and in the case of inkjet both are utilised. Theincreased popularity of non-impact printing to createphotorealistic colour prints created new challenges for therespective dye and pigment manufacturing industries. Forthe dye industry, the challenge was to generate newchromophores and/or higher-purity existing dyes for inkjetand thermal dye transfer, with key attributes such as highpurity, a high extinction coefficient, a narrow absorptionband, ease of transfer, non-toxicity, and good fastness tolight, water, and atmospheric gases. Although the structuresof commercially used thermal dye transfer dyes have notbeen disclosed, the structures of commercially successfulinkjet dyes, which include acid, direct, and passivatedreactive dyes, are predominantly in the public domain. Therole of dye and pigment colorants within the rapidlydeveloping electronic paper (e-paper) field is important forboth existing monochrome systems, e.g. the Amazon Kindlesystem, which uses carbon black and titanium dioxide, andthe potentially successful future colour systems, which willutilise either RGB or CYM dyes or pigments to generate full-colour photo-quality images on screen, together withmoving video images. Thus, it would appear that, althoughtechnological advances continue to be made within theimaging industry, the generation and reproduction of RGBadditive and CYM subtractive images, in whatever form,would seem to be reliant on the use of dyes and/or pigmentcolorants.