HANS - A New Color Separation And Halftoning Paradigm
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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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HANS - A New Color Separation And Halftoning Paradigm
- 1. 2010 © HP HANS A New Color Separation and Halftoning Paradigm Ján Morovič, Peter Morovič & Jordi Arnabat Hewlett–Packard Company Barcelona, Spain
- 2. 2010 © HP What makes printed colors?
- 3. 2010 © HP Anatomy of a color halftone print
- 4. 2010 © HP Anatomy of a color halftone print
- 5. 2010 © HP Anatomy of a color halftone print
- 6. 2010 © HP Print color formation Side view 70% W 13% C 10% K 6% M 1% CM Neugebauerprimaries Relativeareacoverages Subtractive Additive
- 7. 2010 © HP Analog from digital
- 8. 2010 © HP From color to halftone pattern CIE L*a*b* sRGB SWOP CMYK ... color management color appearance model device characterization color enhancement gamut mapping color separation linearization calibration halftoning
- 9. 2010 © HP Controlling print color – a first principles approach
- 10. 2010 © HP How do we get from color to halftone pattern? 20% W 30% C 20% M 0% Y 20% CM 0% CY 0% MY 0% CMY Source color Color management Printable color Halftone pattern’s Neugebauer Primary statistics Halftone pattern
- 11. 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. patterns 1:1 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)
- 12. 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, ...
- 13. 2010 © HP What if we can’t account for / eliminate obstacles Printable color Colorseparation Printed pattern NPacs (matching color) Digital pattern NPacs (resulting in printed patterns matching color) DigitalPrinted [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
- 14. 2010 © HP From theory to practice
- 15. 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% W 30% C 20% M 0% Y 20% 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
- 16. 2010 © HP Does it work?
- 17. 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)
- 18. 2010 © HP Results –!ink use
- 19. 2010 © HP Results – image quality Current (optimal ICC) HANS
- 20. 2010 © HP What next?
- 21. 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)
- 22. 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
- 23. 2010 © HP Thank you!