title: Diffractive parameric colors.
abstract: A method of producing inkless parameric color pairs is studied. In this method, colors are formed additively using diffraction gratings with differing grating periods as primary colors. Gratings with different grating periods reflect different spectral radiance peaks of a fluorescent lamp to the desired viewing angle, according to the grating equation. Four spectral peaks of a 4000 K fluorescent lamp--red, green, cyan, and blue-are used as the primary colors. The colors are mixed additively by fixing the relative areas of different grating periods inside a pixel. With four primary colors it is possible to mix certain colors with different triplets of primary colors. Thus, it is theoretically possible to produce metameric colors. In this study, three parameric color pairs are fabricated using electron beam lithography, electroplating, and hot embossing. The radiance spectra of the color pairs are measured by spectroradiometer from hot-embossed plastic samples. The CIELAB DeltaE(ab) and CIEDE2000 color differences between radiance spectra of the color pairs are calculated. The CIEDE2000 color differences of color pairs are between 2.6 and 7.2 units in reference viewing conditions. The effects of viewing angle and different light sources are also evaluated. It is found that both the viewing angle and the light source have very strong influences on the color differences of the color pairs.
authors.affiliation: Department of Mathematics and Physics, University of Joensuu, Joensuu, Finland. joni.orava@joensuu.fi
authors.forename: Joni
authors.initials: J
authors.lastname: Orava
authors.forename: Noora
authors.initials: N
authors.lastname: Heikkila
authors.forename: Timo
authors.initials: T
authors.lastname: Jaaskelainen
authors.forename: Jussi
authors.initials: J
authors.lastname: Parkkinen