Simulating the colour gamut of ink-jet ink systems on coated and uncoated substrates

Nowadays, research and development in colourants have led to a number of new colourants with a wider colour gamut. It is important to select the widest gamut of colourants at the lowest cost. This study intended to simulate the colour gamut of inkjet inks printed on coated and uncoated substrates using the two-constant Kubelka-Munk theory to obtain the optical properties of the inks: absorption coefficients (K) and the scattering coefficients (S). The K and S values were determined independently. Fourteen dye-based inks, supplied by Canon, were employed for calibration of prints to determine their optical properties on coated and uncoated substrates. Spreadsheets and the Visual Basic codes were developed to make the calculations much easier. The nonlinear relationship between absorption coefficients and concentration of inkjet ink (C) was characterised by a power series of the equation K = aC+bC²+cC³ for all wavelengths. The correction coefficients for coated paper (PR-101) found as rₑ,sub, rᵢ,sub, rₑ,print and rᵢ,print were 0.021, 0.600, 0.007 and 0.600, respectively. This resulted in the average colour difference, ∆Eab*, between the predicted reflectance and the measured reflectance of 4 when the single colour of fourteen dyes was investigated. The application of gamut simulation gave a good performance. The four colour inkset giving the largest gamut was the inks that contained Direct Blue 199, Acid Magenta 1, Direct Yellow 86, and Direct Black (reddish). This inkset covered hue of the wool digital image (SHIPP) but it could not cover the lightness of wool picture of 11.7-100.0. The lowest and the highest lightness that this inkset can produce are about 22.8 and 92.5