RGB colour printing and halftoning for the reproduction of structural colour images

Parraman, Carinna; Klein, Susanne; Vazquez, Abigail; Fuller, Harrie

Abstract

Commercial CMYK halftone printing involves additive and subtractive colour mixing that requires the optical mixing of primary colour hues using different-sized dots to obtain variations in reflected colour.
Structural colour, as seen in nature, such as in birds, butterflies and shells, is based on the scattering of light that uses micron to submicron structures to reflect specific wavelengths of light.
Similar to CMYK printing, so-called RGB special effect pigment colours mimic the appearance of these structures by combining additive and subtractive methods to create a range of colours. Similar to structural colour, these pigments, when printed, are highly dynamic in their angle of appearance and surface scattering. This dynamic appearance also presents new problems both in terms of reproduction, appearance and measurement.
We have studied the influence of different halftone structures on an RGB print using various printing methods. First-order, second-order, and structure-aware FM halftoning algorithms were applied to produce different spatial combinations of inks on the printed surface.
The images must be printed on a black substrate, and the pigments present quite an unusual gamut. The image content of the print needs to be chosen carefully, which, erring towards the blue-green area of the spectrum, has a strong correlation with images that exploit the original features ie feathers and beetle shells.
We aim to optimise the printing method and halftone pattern to reproduce particular images. This paper will present how different structure-aware halftones improve the representation of image structures and details.
Halftone structures differ in the spatial distribution of dots. For instance, in first-order FM halftones, single dots are distributed stochastically, where the size of dots is constant while their density is changed. In second-order FM (also known as stochastic cluster-dot halftone), the size and the distance between dots are variable. To improve the reproduction of structural detail, the structure-aware algorithm seeks to place dots in line with the high-frequency areas of the image.

• Presentation Conference Type: Presentation / Talk
• Conference Name: Color Impact 2023
• Start Date: Jun 11, 2023
• End Date: Jun 15, 2023
• Deposit Date: Aug 9, 2023
• Publicly Available Date: Aug 9, 2023
• Series Title: Inter Society Color Council
• Public URL: https://uwe-repository.worktribe.com/output/11015048