© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
THE SPECTRAL PRINTER: FROM TECHNICAL CHALLENGE TO BUSINESS CASE
Dr. Ján MorovičSenior Color Scientist / Master Technologist, Hewlett–Packard CompanyDirector of CIE Division 8: Image Technology
8th ROND Conference, 14th March 2013, Örnsköldsvik, Swedenhttp://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 moneyfrom it?
WHICH COMES FIRST?
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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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
WHAT IS SPECTRAL PRINTING?
Match original under any light source.Match for all observers (human, animal).→ Reproduction changes with illumination like the original does and for all viewers.
‘I can see what the Mona Lisa would look like in my living room’
BUT: “Match” is aim, not necessarily property!
Light sourceLight source
Light source 1
O P
Light source 2
O P
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SO, WHAT IS COLOR PRINTING?
Designed to match color under one light source (D50) and for human observers with certain cone sensitivities.
BUT: • ∆Es even under chosen light source• Uncontrolled/unknown ∆Es under other light sources
Assumption: for a spectral print, color differences under variety of light sources are lower than for colorimetric (metameric) print.
Light sourceLight source
Light source 1
O P
Light source 2
OPP?
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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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
HOW DO I MAKE A SPECTRAL PRINT?
Matching
Halftoning Colorants Substrate
Spectral content
Gamut mapping
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
WHERE CAN I GET SPECTRAL CONTENT?
• 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
Spectral content Gamut mapping Matching Halftoning Colorants Substrate
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
HOW DO I ADAPT IT TO MY MATERIALS?
• Single-shot mapping
• Direct spectrum → colorant amounts mapping (optimization/regression, computationally expensive, disregards visual system entirely) (e.g., Bastani et al., 2006)
• Gamut mapping + Matching
• Color gamut mapping to gamut of 3 fundamental bases + spectral mapping in metameric blacks (Chau and Cowan, 1996)
• Sequential color mapping: match under illuminant U, then to V in remaining metamer set, then to W, etc. (Urban et al., 2008)
• Workflow considerations
• LabPQR (Derhak and Rosen, 2004) → extension of ICC framework, easy WF integration
• Result: spectrum to colorant amounts
Spectral content Gamut mapping Matching Halftoning Colorants Substrate
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TWO-STAGE MAPPING & LABPQR
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HOW DO I BUILD COLORANT PATTERNS?
• Challenges:
• Multiple colorants (CMYK+)
• Difficulty of applying threshold matrix halftoning (AM/FM) → moire
• Potentially abrupt changes in colorant space → artifacts
• Solutions:
• Error diffusion (Norberg, 2012)
• BUT: “arbitrary” multi-colorant patterns challenging
Spectral content Gamut mapping Matching Halftoning Colorants Substrate
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AN ALTERNATIVE: HANSSpectral content Gamut mapping Matching Halftoning Colorants Substrate
tesserae/ tiles!
Neugebauer Primaries (NPs) / at-pixel ink drop states!
artist!
mosaic! pr
int!
printer (inks, media, WS, FW, pipeline)!
Printing as mosaic assembly
Separation: colorant amount selection → Neugebauer Primary
(NP) statistics
Halftoning: per colorant continuous levels to discrete drops → NP per
pixel from local statistics
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
AN ALTERNATIVE: HANSSpectral content Gamut mapping Matching Halftoning Colorants Substrate
gamut mapping
reflectance reflectance
colorantmatching
colorant vector
colorant space
halftoning
drops / pixel /
colorant
NPmatching
NP area coverage
vector
NP space halftoning
colo
rant
w
orkfl
owH
ANS
wor
kflow
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
AN ALTERNATIVE: HANSSpectral content Gamut mapping Matching Halftoning Colorants Substrate
• The reflectance of a pattern is the convex, area-coverage-weighted combination of it’s NPs’ reflectances (corrected for dot gain) → YNSN
• A reflectance can be matched if there exists a simplex in reflectance space, that has the reflectances of a printing system’s NPs as its vertices
• The area coverages that need to be assigned to each NP match the convex weights with which it needs to be 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!
Alternative basic NPacs:!
6086!(in 34=81D)!
Alternative basic ink combinations:!2!(in 4D)!
C=34%!M=27%!Y=28%!
C=7%!Y=1%!K=27%!
W=77%!C1=1%!Y1=2%!K1=20%!
W=79%!Y1=2%!K1=14%!Y1K1=2%!C2=1%!K2=2%!
W=70%!C1=2%!M1=5%!Y1=5%!K1=6%!C1M1=1%!C1K1=2%!M1K1=3%!Y1K1=2%!C2=4%!
Print color!
3000x possible
patterns (same color)!
included!
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
AN ALTERNATIVE: HANSSpectral content Gamut mapping Matching Halftoning Colorants Substrate
• 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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
COLORANTS AND SUBSTRATE
• What colorants are best for spectral reproduction?
• Several studies (e.g., Tzeng, 1999)
• Narrow-band, inverted Gaussians (from first principles; Chen, 2004)
• BUT, constraints from:
• what is physically realizable
• what can be manufactured in bulk
• what can be successfully jetted or deposited using other marking engines
• Substrate’s colorant limit (rules out Gaussians)
Spectral content Gamut mapping Matching Halftoning Colorants Substrate
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
COLORANTS AND SUBSTRATESpectral content Gamut mapping Matching Halftoning Colorants Substrate
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WILL MY CUSTOMERS SEE THE DIFFERENCE?
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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)
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MIPE: AN EXPERIENCE–BASED METRIC
20
Paramers (>0 ∆E even under
‘reference’ illuminant)
Non-parametric descriptive statisticsMedian: how close a match can be
expected for an arbitrary, but realistic, light source
95th percentile – median: how much this match varies
Maximum: how far apart the two can get at worst
Light sources / illuminantsCIE standard and recommended illuminants
+ measured light sources
Color differencewith visually meaningful
units (~JND)
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
SPECTRAL ‘GOODNESS’ OF METAMERIC PRINT
Colorimetric ‘goodness’ Spectral ‘goodness’
matte glossy
HP Designjet Z310010 inks: cMmYnNKRGB + glossy/matte black + gloss enhancer
Spot color: PANTONE uncoated, matte and coated, 1224 patches per substrate (3672 total samples; mixtures of Pantone system’s 15 base inks)Fine art: 1168 measurements taken from paintings
• 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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
SPECTRAL ‘GOODNESS’ OF SPECTRAL PRINT
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
CAN I MAKE MONEY FROM IT?
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
ADDRESSABLE MARKET ($846B IN 2016 WW)
1%2%3%4%4%
5%
8%
13%
18%
43%
Packaging Commercial Advertising Magazines NewspapersBooks Catalogues Office Directories Security
14%
86%
Potentiallyspectral
Non-spectral
$364B
Source: PIRA
$118B
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
SPECTRAL APPLICATIONSApplication Feasibility Salability
Proofinghigher (content available, matching has good chances ← similar materials)
higher (similarity to production print is essence of proof → spectral is clearly
better than metameric proof)
Fine-art reproduction medium (content availability limited, material differences greater)
medium (spectral match to original may not always be desired → Mona Lisa in Louvre v. my
kitchen)
Catalogues lower (content scarce, materials potentially very different)
higher (color differences are source of many returned good, better reproduction → more
profitable operation)
Security higher (spectral differences are created among available metamer sets, not v. original)
higher (persistent need for ever broadening variety of features; closer ties to original materials if spectral properties exploited)
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
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)
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
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
© Copyright 2013 Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice.
ACKNOWLEDGEMENTS
• Peter Morovič
• Juan Manuel García-Reyero
• Martí Rius
• Jordi Arnabat
• Johan Lammens
• Carlos Amselem
• Ole Norberg
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THANK YOU!