Spectral printing is a well–established part of imaging that can boast of a rich body of literature. Nonetheless there has been limited commercial uptake of this approach to visual content reproduction, in spite of its clear benefits. The aim of the present paper is therefore to explore what may lie behind this apparent mismatch by looking at how colorimetric (metameric) and spectral reproduction compare on an 11–ink printing system. To aid the above exploration, the paper proposes a new metric for evaluating spectral reproduction in a visually meaningful way and presents an analysis of the spectral properties of colorimetric and spectral reproductions of a variety of original content including spot colors and fine art.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Revisiting Spectral Printing: A Data Driven Approach P. Morovič, J. Morovič, J. Arnabat and J. M. García–Reyero Hewlett Packard Company, Sant Cugat del Vallés, Catalonia, Spain
Spectral printing has clear benefits! - Match original under any light source - Match for all observers (human, animal) - à reproduction changes with illumination
in the same way as the original does, for all observers (‘I can see what the Mona Lisa would look like in my living room’)
What is needed? - Spectral content (little point in matching RGBs) - Multi-ink printers (metamerism is needed)
- Spectral control of output (print properties need to be chosen based on expected spectra)
- Printers that span sufficient spectral gamut (on a chosen substrate) to expected content
Many metrics defined in the literature - Purely spectral, taking into account CMFs, focusing on metamerism between specific light
sources, looking at sets of color difference statistics per light source + combinations of these
BUT: how does an observer experience the goodness of a spectral match? - Original – print ß observer
- Observer views original-print-pair under many light sources (not arbitrary à database of measured lights)
- Under each light source they see certain levels of color difference (à most accurately predicted by ∆E2000, with JND units)
- Surveying their experiences from under multiple light sources gives rise to a variety of color difference magnitudes (à choice of relevant statistics)
How good a spectral match is the result of matching colorimetry?
Results: colorimetrically derived print
Colorimetric ‘goodness’ Spectral ‘goodness’
- Broadly similar performance under D50 (for which colorimetry was matched) and all other 172 illuminants (color gamut differences a big contributor already)
- MIPE errors higher than D50 ∆Es (sanity check for maximum)
- Gap between MIPE and D50 ∆Es indicates room for improvement from spectral matching
Spectral printing has clear benefits in some cases (e.g., Fine art on glossy), but: - Spectral matching of colorimetric prints is often as good as or close to it (e.g., no benefit for
spot colors in this case)
- Maximizing the benefit of fully spectral printing requires highly accurate matching and high repeatability
- Further improvements could be expected from ink–sets optimized for spectral printing (although constrained options using manufacturable materials)
- Biggest benefits will be in specialty applications (e.g., Hersch ’11 security printing)
Is spectral going to replace colorimetric printing? Not anytime soon …