HANS: Enabling CMY Metamers
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This document discusses a new approach to color management called Halftone Area Neugebauer Separation (HANS) that directly controls the Neugebauer primary area coverages to optimize print attributes like ink usage. Traditional approaches control ink amounts, but HANS operates in a higher-dimensional Neugebauer primary space, allowing for more print options or "metamers". Test results showed HANS was able to reduce ink usage compared to traditional approaches. Challenges include printer model accuracy and computational efficiency, but benefits include greater optimization possibilities and a framework that is agnostic to inkset complexity.
HANS: Enabling CMY Metamers
- 1. HANS Enabling CMY Metamers J叩n Morovi, Peter Morovi & Juan Manuel Garc鱈a-Reyero HewlettPackard Company Barcelona, Spain Presented at ICC/HP Digital Print Day, 15th June 2011 201 息 HewlettPackard Company 1
- 2. What makes printed colors? 201 息 HewlettPackard Company 1
- 3. Print color formation Side view Additive Relative area coverages Neugebauer primaries 70% W 13% C 10% K 6% M Subtractive 1% CM 201 息 HewlettPackard Company 1
- 4. Analog from digital 201 息 HewlettPackard Company 1
- 5. From color to halftone pattern color separation color management CIE L*a*b* linearization color appearance model sRGB calibration device characterization SWOP CMYK halftoning color enhancement ... gamut mapping 201 息 HewlettPackard Company 1
- 6. Controlling print color a 鍖rst principles approach 201 息 HewlettPackard Company 1
- 7. How do we get from color to halftone pattern? Halftone patterns Neugebauer Primary Halftone Source color Color management Printable color statistics pattern 20% W 30% C 20% M 0% Y 20% CM 0% CY 0% MY 0% CMY 201 息 HewlettPackard Company 1
- 8. How does this differ from traditional color control? Traditional New How much area should How much of each ink I cover with each Color should I use for each Neugebauer Primary separation color? Output: Neugebauer Output: ink amounts primary area coverages Decides where to place Decides where to place ink drops based on ink drops based on color color separation Halftoning separation constraints. constraints. Controls: spatial and Specifying Neugebauer Primary area coverages provides access Controls: spatial overprinting properties properties only to vastly greater space of printable patterns. kn v. n Ink (for system where up to k-1 ink drops per pixel can be speci鍖ed for n inks) amounts v. 1:1 1:many patterns 201 息 HewlettPackard Company 1
- 9. From theory to practice 201 息 HewlettPackard Company 1
- 10. A minimal Halftone Area Neugebauer Separation setup (CMYK, 1bpp) 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 Print & measure Compute convex Find printable Barycentric Select one NP per Neugebauer primary hull & tetrahedralize colors enclosing coordinates are pixel & diffuse (NP) CIE XYZs hull NPs tetrahedron vertex NP areas NPac-NP error 201 息 HewlettPackard Company 1
- 11. Optimizing HANS Form all polyhedra using the kn NPs Find all colors for which NPacs are to be optimized enclosed by each polyhedron Compute barycentric coordinates Evaluate each candidate (grain, ink use, color constancy, ...) Assign combined score Select best NPac for each color CMY 1dpp: kn=23=8 163 polyhedra CMYK 1dpp: kn=24=16 64839 polyhedra CMYKcm 2dpp: kn=36=729 2.8x10219 polyhedra 201 息 HewlettPackard Company 1
- 12. Reductio ad absurdum the CMY case With traditional, colorant space control: no metamers each in-gamut color matched by one CMY colorant amount combination Even at max. 1 drop per pixel, CMY colorant set has 23=8 Neugebauer Primaries 3D colorimetric space to 8D NP space results in 1:many mapping 163 polyhedra span gamut and provide metamers midgray: 115 metamers mean 13% ink use difference between metamer using most and least ink for each color More metamers still if more than one drop per pixel is used 201 息 HewlettPackard Company 1
- 13. Does it work? 201 息 HewlettPackard Company 1
- 14. Test setup: Can we 鍖nd 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 work鍖ows 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) 201 息 HewlettPackard Company 1
- 15. Results ink use 201 息 HewlettPackard Company 1
- 16. What next? 201 息 HewlettPackard Company 1
- 17. Challenges and bene鍖ts Challenges: printer model accuracy (the more accurate the better the optimization) computational ef鍖ciency (weeks of computation per substrate) optimization (ef鍖cient models of print attributes, ef鍖cient traversal of NPac space) Bene鍖ts: greater & direct optimization (more from the same printer-ink-substrate) explicit tradeoff among print attributes (grain v. ink use v. color constancy) inkset agnosticism (same process for CMY 1bpp and CMmYKkNnRGB 2bpp) More detail at this years IS&T/SID Color and Imaging Conference (subject to acceptance) 201 息 HewlettPackard Company 1
- 18. Acknowledgements Lluis Abello Alan Lobban Carlos Amselem scar Martinez Xavi Bruch Scott Norum Gary Dispoto Michel Encrenaz Aleix Oriol I-Jong Lin Eduard Garcia Ramon Pastor John Recker Oriol Gasch Yvan Richard Ingeborg Tastl Rafa Gimenez Aurora Rubio Bob Ulichney Dudi Bakalash Josep Girlat Utpal Sarkar Lahav Langboim Rafael Goma Albert Serra Shay Maoz Andr辿s Gonzalez Jep Tarradas Amir Sheinman Jacint Hument Joan Uroz Alex Veis Johan Lammens Jordi Vilar Igor Yakubov 201 息 HewlettPackard Company 1