The Spectral Printer: From Technical Challenge To Business Case

THE SPECTRAL PRINTER:
FROM TECHNICAL CHALLENGE TO BUSINESS CASE

Dr. Ján Morovič
Senior Color Scientist / Master Technologist, Hewlett–Packard Company
Director of CIE Division 8: Image Technology
8th ROND Conference, 14th March 2013, Örnsköldsvik, Sweden
http://fotonerdz.deviantart.com/art/Matrix-spectrum-278731679
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.

Can we
make it?

Can we
make money
from it?

WHICH COMES FIRST?

OUTLINE

• What is spectral printing? (Again!)
• Can we make it?
• Technology: inks, substrates, gamut, separation, workﬂow, content
• Customer beneﬁt: “Will I see it?”
• Can we make money from it?
• Market size: how many billion pages/$?
• Added value: premium pricing / new applications?
• Conclusions

WHAT IS SPECTRAL PRINTING?

Match original under any light source. Light source 1
Match for all observers (human, animal).
→ Reproduction changes with illumination like the O P
original does and for all viewers.

‘I can see what the Mona Lisa would look like Light source 2
Light source
in my living room’ Light source
O P
BUT: “Match” is aim, not necessarily property!


SO, WHAT IS COLOR PRINTING?

Designed to match color under one light source (D50) and Light source 1
for human observers with certain cone sensitivities.
O P
BUT:
• ∆Es even under chosen light source
• Uncontrolled/unknown ∆Es under other light sources Light source 2
Light source
Light source
Assumption: for a spectral print, color diﬀerences under
variety of light sources are lower than for colorimetric
(metameric) print.
O ? P
P

ANY OTHER ‘SPECTRAL’?

• Focus here on spectral printing (i.e., aiming at a match
of spectral reﬂectance between original and
reproduction).

• Spectral data also has beneﬁts for metameric
reproduction
• Metameric match under non-standard / multiple
light sources
• Modeling of colorant interactions (e.g. spot color
overprinting)
• Modeling of printer behavior

HOW DO I MAKE A
SPECTRAL PRINT?

Spectral Gamut
Matching
content mapping

Halftoning Colorants Substrate


WHERE CAN I GET SPECTRAL CONTENT?
Spectral content Gamut mapping Matching Halftoning Colorants Substrate

• Spectral image capture → broadly applicable, but still scarce
• Spectral measurement → applicable to color palettes (e.g., Pantone)
• Predicted from original device’s model → when original is a print,
spectra can be predicted using model of it’s colorants and halftoning
• Predicted from colorimetry / trichromatic capture → colorimetric
capture + measurements to characterize spectral basis (e.g., of artwork)

• Without spectral content, spectral printing is inapplicable
→ not going to replace metameric color reproduction wholesale


HOW DO I ADAPT IT TO MY MATERIALS?

• Single-shot mapping • Sequential color mapping: match under
illuminant U, then to V in remaining
• Direct spectrum → colorant amounts
metamer set, then to W, etc. (Urban et al.,
mapping (optimization/regression, 2008)
computationally expensive, disregards
visual system entirely) (e.g., Bastani et al., • Workﬂow considerations
2006) • LabPQR (Derhak and Rosen, 2004) → extension
• Gamut mapping + Matching of ICC framework, easy WF integration
• Color gamut mapping to gamut of 3
fundamental bases + spectral mapping in • Result: spectrum to colorant amounts
metameric blacks (Chau and Cowan, 1996)


TWO-STAGE MAPPING & LABPQR


HOW DO I BUILD COLORANT PATTERNS?

• Challenges: • Error diﬀusion (Norberg, 2012)
• Multiple colorants (CMYK+) • BUT: “arbitrary” multi-colorant
patterns challenging
• Diﬃculty of applying threshold matrix
halftoning (AM/FM) → moire
• Potentially abrupt changes in colorant
space → artifacts
• Solutions:


AN ALTERNATIVE: HANS

printer
(inks, media, WS, FW, pipeline)!

artist!

Printing as mosaic assembly

Separation: colorant amount
selection → Neugebauer Primary

mosaic!
(NP) statistics

print!
Halftoning: per colorant continuous
levels to discrete drops → NP per
pixel from local statistics

tesserae/ Neugebauer Primaries (NPs) /
tiles!
at-pixel ink drop states!

Spectral content
workflow Gamut mapping Matching Halftoning Colorants Substrate
colorant

colorant
colorant colorant
space
matching vector
halftoning

drops /
gamut
reflectance reflectance pixel /
mapping
colorant
workflow

NP area
NP NP space
HANS

coverage
matching halftoning
vector



Alternative basic Alternative basic
• The reflectance of a pattern is the convex, area-coverage- ink combinations:! Print color! NPacs:!
2! 6086!
weighted combination of it’s NPs’ reflectances (corrected for (in 4D)! (in 34=81D)!

dot gain) → YNSN 3000x
possible
patterns (same
• A reflectance can be matched if there exists a simplex in color)! W=70%!
C1=2%!
reflectance space, that has the reflectances of a printing M1=5%!
Y1=5%!
system’s NPs as its vertices W=79%!
Y1=2%!
K1=6%!
C1M1=1%!
W=77%! K1=14%! C1K1=2%!
• The area coverages that need to be assigned to each NP C=34%!
M=27%!
C=7%!
Y=1%!
included! C1=1%!
Y1=2%!
Y1K1=2%!
C2=1%!
M1K1=3%!
Y1K1=2%!
match the convex weights with which it needs to be Y=28%! K=27%! K1=20%! K2=2%! C2=4%!

combined to match the target spectrum
• Operating in NP space offers vastly more choice: n versus kn
dimensions (for n colorants and k levels per colorant per pixel)
• E.g., for 6-ink printer with up to 3 drops per ink per pixel,
HANS has 46=4096D versus the 6D of a colorant workflow
• The rest is brute (or not so brute) force!



• HANS error diﬀusion:
• Error is computed in area coverage
terms
• Area coverages account for optically-
additive aspect of print color formation
• Arbitrary NP combinations can be
formed and transitioned between
• Non-linearity of colorant interactions is
handled prior to halftoning, which can then
operate in an additive space

COLORANTS AND SUBSTRATE

• What colorants are best for spectral • what is physically realizable
reproduction? • what can be manufactured in bulk
• Several studies (e.g., Tzeng, 1999) • what can be successfully jetted or
• Narrow-band, inverted Gaussians deposited using other marking
(from ﬁrst principles; Chen, 2004) engines
• Substrate’s colorant limit (rules out
Gaussians)

• BUT, constraints from:

COLORANTS AND SUBSTRATE


WILL MY CUSTOMERS SEE THE DIFFERENCE?


WHAT MAKES A GOOD SPECTRAL PRINT?
• 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 ← observer
• Observer views original-print-pair under many light sources
(not arbitrary → database of measured lights)
• Under each light source they see certain levels of color difference
(→ 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 (→ choice of relevant statistics)


MIPE: AN EXPERIENCE–BASED METRIC
Color diﬀerence
with visually meaningful
units (~JND)
Paramers
(>0 ∆E even under
‘reference’ illuminant)

20

Non-parametric descriptive statistics
Median: how close a match can be
expected for an arbitrary, but
realistic, light source
95th percentile – median: how much this
Light sources / illuminants match varies
CIE standard and recommended illuminants Maximum: how far apart the two can get
+ measured light sources at worst


SPECTRAL ‘GOODNESS’ OF METAMERIC PRINT
Colorimetric ‘goodness’ Spectral ‘goodness’

• Similar performance under D50 (for
Spot color: PANTONE uncoated, matte and coated, 1224
patches per substrate (3672 total samples; mixtures of which colorimetry was matched) and
Pantone system’s 15 base inks)
Fine art: 1168 measurements taken from paintings all other 172 illuminants (color
gamut diﬀerences a big contributor
already)
matte glossy • MIPE errors higher than D50 ∆Es
HP Designjet Z3100 (sanity check for maximum)
10 inks: cMmYnNKRGB • → Gap between MIPE and D50 ∆Es
+ glossy/matte black +
gloss enhancer indicates room for improvement from
spectral matching

SPECTRAL ‘GOODNESS’ OF SPECTRAL PRINT


TECHNICAL CHALLENGES

• Degree of “spectral goodness” benefit versus metameric reproduction
• spectral workflow + inherent limits of materials used
• more colorants ≠ better spectral performance (necessary but not sufficient)
• Way forward:
• Dedicated spectral reproduction colorants
• Efficient spectral workflow
• Experience-focused optimization
• Availability of content

STANDARDS? (A.K.A. THE CIE SALES PITCH)

• CIE Technical Committee 8-07 Multispectral
Imaging (chair: Masahiro Yamaguchi)
• Terms of reference: To study, develop and
recommend encoding techniques and data
formats for the exchange of multispectral
images, and to provide test procedures for the
evaluation of multispectral imaging systems.
• Technical report due end ’13: will provide basics
of multispectral format requirements &
compare four alternative formats

CAN I MAKE MONEY FROM IT?


ADDRESSABLE MARKET ($846B IN 2016 WW)
$118B
3% 1%
2% 14%
4%
4% Potentially
5% spectral

8% 43%
$364B

13%
Non-spectral
18% 86%

Packaging Commercial Advertising Magazines Newspapers
Books Catalogues Oﬃce Directories Security
Source: PIRA

SPECTRAL APPLICATIONS
Application Feasibility Salability

higher (similarity to production print is
higher (content available, matching has
Proofing essence of proof → spectral is clearly
good chances ← similar materials)
better than metameric proof)

medium (spectral match to original may not
medium (content availability limited, material
Fine-art reproduction always be desired → Mona Lisa in Louvre v. my
differences greater)
kitchen)

higher (color differences are source of many
lower (content scarce, materials potentially
Catalogues returned good, better reproduction → more
very different)
profitable operation)

higher (persistent need for ever broadening
higher (spectral differences are created
Security variety of features; closer ties to original
among available metamer sets, not v. original)
materials if spectral properties exploited)

WHERE DOES THE MONEY COME FROM?

• “Better” reproduction → proof, fine art print
• New features → security
• Secondary benefits → reduction lost profit from
returned goods (catalogues)

• Premium pricing v. differentiation from competitors
(print as commodity)


A TALE OF TWO PRINTERS

• Printer A: the hunting knife
• Dedicated spectral printing colorants & printing technology + spectral workﬂow
•

+ Excels at spectral printing; limited addressable market
•

- Not suitable for ‘color’ printing (ink use, grain, cost)
• Printer B: the Swiss Army knife
• General purpose materials & technology (+ spectral workﬂow)
•

+ Suitable for spectral or ‘color’ printing; large addressable market
•

- Less spectrally accurate than Printer A

CONCLUSIONS

• There are multiple applications that can beneﬁt from spectral printing
• Colorants developed speciﬁcally for spectral printing would boost its potential
• Solutions need to focus on customer/viewer experience


ACKNOWLEDGEMENTS

• Peter Morovič • Ole Norberg
• Juan Manuel García-Reyero
• Martí Rius
• Jordi Arnabat
• Johan Lammens
• Carlos Amselem


THANK YOU!

The Spectral Printer: From Technical Challenge To Business Case

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