hans - a new color separation and halftoning paradigm
DESCRIPTION
Slides shown at 18th Color and Imaging Conference in San Antonio, TX on 12 November 2010. Please, refer to conference paper for details.TRANSCRIPT
2010 © HP
HANSA New Color Separation and Halftoning Paradigm
Ján Morovič, Peter Morovič & Jordi ArnabatHewlett–Packard CompanyBarcelona, Spain
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What makes printed colors?
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Anatomy of a color halftone print
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Anatomy of a color halftone print
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Anatomy of a color halftone print
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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
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Analog from digital
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From color to halftone pattern
CIE L*a*b*sRGB
SWOP CMYK...
color managementcolor appearance modeldevice characterization
color enhancementgamut mapping
color separationlinearizationcalibrationhalftoning
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Controlling print color – a first principles approach
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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
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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)
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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, ...
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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
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From theory to practice
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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
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Does it work?
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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)
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Results –!ink use
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Results – image quality
Current(optimal ICC) HANS
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What next?
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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)
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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
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Thank you!