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Slides shown at 18th Color and Imaging Conference in San Antonio, TX on 12 November 2010. Please, refer to conference paper for details.
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2010 © HP
HANSA New Color Separation and Halftoning Paradigm
Ján Morovič, Peter Morovič & Jordi ArnabatHewlett–Packard CompanyBarcelona, Spain
2010 © HP
What makes printed colors?
2010 © HP
Anatomy of a color halftone print
2010 © HP
Anatomy of a color halftone print
2010 © HP
Anatomy of a color halftone print
2010 © HP
Print color formation
Side view
70% W13% C10% K 6% M 1% CM
Neug
ebauer p
rimaries
Rel
ativ
e ar
ea c
ove
rag
es
Subtractive
Additive
2010 © HP
Analog from digital
2010 © HP
From color to halftone pattern
CIE L*a*b*sRGB
SWOP CMYK...
color managementcolor appearance modeldevice characterization
color enhancementgamut mapping
color separationlinearizationcalibrationhalftoning
2010 © HP
Controlling print color – a first principles approach
2010 © HP
How do we get from color to halftone pattern?
20% W30% C20% M 0% Y20% CM 0% CY 0% MY 0% CMY
Source color Color management Printable color
Halftone pattern’s Neugebauer Primary
statisticsHalftone pattern
2010 © HP
How does this differ from traditional color control?
Traditional New
Color separation
‘How much of each ink should I use for each
color?’Output: ink amounts
How much area should I cover with each
Neugebauer Primary’Output: Neugebauer
primary area coverages
Halftoning
Decides where to place ink drops based on color separation constraints.Controls: spatial and
overprinting properties
Decides where to place ink drops based on
color separation constraints.
Controls: spatial properties only
Ink amounts v.
patterns1:1 1:many
Specifying Neugebauer Primary area coverages provides access to vastly greater space of printable patterns.
kn v. n(for system where up to k-1 ink drops per pixel can be specified for n inks)
2010 © HP
Neugebauer primary area coverages: nightmare or walk in the park?
• Specifying Neugebauer Primary area coverages (NPacs)
• Selecting point in kn dimensions versus n (e.g., 46=4096D NPac space for CMYKcm printer with max. 3 drops per pixel per ink versus 6D ink space)
• Efficiently and effectively traversing high dimensional space
• Accurately predicting NPac colorimetry
• Obtaining NPac statistics on paper
• Trivial if ink drops were tessellating, uniform, perfectly–square and not subject to optical dot–gain :)
• BUT: difficult to do accurately due to dot gain, colorant layer thickness variation, substrate surface properties, ink-substrate interaction, ink–ink interaction, drop shape, drop placement errors, mis-registration, ...
2010 © HP
What if we can’t account for / eliminate obstacles
Printable color
Col
or s
epar
atio
n
Printed pattern NPacs (matching color)
Digital pattern NPacs (resulting in printed
patterns matching color)
Dig
ital
Prin
ted
[W,C,M,CM]=[0,0.5,0.5,0]
[W,C,M,CM]=[0.05,0.45,0.35,0.15]
[W,C,M,CM]=[0.5,0,0,0.5]
[W,C,M,CM]=[0.35,0.15,0.1,0.40]
digital NPac vectors > printable NPac vectors >> ink vectors
2010 © HP
From theory to practice
2010 © HP
A minimal Halftone Area Neugebauer Separation setup (CMYK, 1bpp)
Print & measure Neugebauer primary
(NP) CIE XYZs
Compute convex hull & tetrahedralize
hull NPs
Find printable color’s enclosing
tetrahedron
Printable color
20% W30% C20% M 0% Y20% CM 0% CY 0% MY 0% CMY 0% K 0% KC 0% KM 0% KY 0% KCM 0% KCY 0% KMY 0% KCMY
Barycentric coordinates are vertex NP areas
Select one NP per pixel & diffuse NPac-NP error
2010 © HP
Does it work?
2010 © HP
Test setup: ‘Can we find NPacs that use less ink?’
• Printer: HP Designjet L65500
• Inks: CMYKcm latex
• Substrate: Avery Self-Adhesive Vinyl
• Color samples: 748 Lab-uniform ISO coated v. 2 samples
• Color workflows compared:
• Ink space separation, GCR optimized for low grain, ink space halftoning (current default)
• Ink space separation, maximum GCR optimized for low grain, ink space halftoning (current optimal)
• NPac space separation (optimized for minimum ink use) and halftoning (HANS)
2010 © HP
Results –!ink use
2010 © HP
Results – image quality
Current(optimal ICC) HANS
2010 © HP
What next?
2010 © HP
Challenges and benefits
• Challenges:
• printer model accuracy (the more accurate the better the optimization)
• computational efficiency (weeks of computation per substrate)
• optimization (efficient models of print attributes, efficient traversal of NPac space)
• Benefits:
• greater & direct optimization (more from the same printer-ink-substrate)
• explicit trade–off among print attributes (grain v. ink use v. color constancy)
• inkset agnosticism (same process for CMY 1bpp and CMmYKkNnRGB 2bpp)
2010 © HP
Acknowledgements
– Dudi Bakalash– Lahav Langboim
– Shay Maoz– Amir Sheinman
– Igor Yakubov
– Gary Dispoto– I-Jong Lin
– John Recker– Ingeborg Tastl
– Bob Ulichney
– Michel Encrenaz
– Eduard Garcia– Joan Manel Garcia
– Oriol Gasch– Rafael Gimenez– Rafael Goma
– Andrés Gonzalez– Jacint Hument
– Johan Lammens– Alan Lobban
– Scott Norum
– Aleix Oriol– Ramon Pastor
– Yvan Richard– Aurora Rubio– Albert Serra
– Jep Tarradas– Joan Uroz
– Jordi Vilar
2010 © HP
Thank you!