8 vertex HANS: An ultra-simple printer color architecture
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Co-authors: Peter Morovic, Martí Rius and Juan Manuel García-Reyero. Presented at 21st IS&T Color and Imaging Conference on 8th November 2013. "The underlying non-linearity of how print colorants combine makes color control in printing significantly more complex than for other color imaging devices. While in additive systems a measurement of their few primaries and per-channel non-linearities versus luminance is a sufficient basis for predicting color output, printing typically requires the measurement of a large number of colorant combinations. This requirement for many measurements makes accurate color output more challenging and means that setting up a printing system’s color control can be time consuming and costly. The solution presented in this paper involves a new use of the HANS approach, which instead of print optimization looks for simplifying print color formation and therefore also control. In a nutshell this can be achieved by only ever combining eight basic colorant patterns, which results in a display-like color gamut and allows for color control on the basis of their eight measurements and those of the printing system’s optical dot gain."
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8 vertex HANS: An ultra-simple printer color architecture
- 1. eight Vertex hans an ultra &mple printÄ color architecture Ján Morovič, Peter Morovič, Martí Rius and Juan Manuel García–Reyero Hewlett–Packard Española S. L., Barcelona, Catalonia, Spain Presented on 8th November 2013 at 21st IS&T Color and Imaging Conference, Albuquerque, NM © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 2. utline O Background Experimental setup & results HANS introduction Conclusions A minimal print color architecture Acknowledgements • Associativity of convex combinations • Cube-shaped gamut • The eight-pattern printer © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 3. ackground B HP Designjet Z5400 Color management Color calibration Color separation LUT 93, 173, 333, 94, 174… © Copyright 2013 Hewlett-Packard Development Company, L.P. Color calibration LUT N x 9, N x 17, …
- 4. ackground B HP Designjet Z5400 Color management 100s-1000s print + measure Color calibration 10s- 1000s-10Ks nodes Color separation LUT 93, 173, 333, 94, 174… © Copyright 2013 Hewlett-Packard Development Company, L.P. 100s print + measure + nodes Color calibration LUT N x 9, N x 17, …
- 5. ackground B Why do we need so much printing & measurement? • Print control in colorant space → non-linear channels & their combinations v. colorimetry • Color separations from RGB/CMYK to colorants non-linear too • Previous work to optimize choice of samples needed: Monga and Bala, 2008; Morovič et al., 2010; Bianco and Schettini, 2012 … © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 6. Pivot the problem: make system simpler instead of characterizing complexity © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 7. a minimal print /lor architecture Associativity of convex combinations + Cube-shaped gamut = The eight-pattern printer © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 8. ans basics H Colorant control Build patterns per colorant & overlay result Colorant vector 2 basic choices! 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%! Halftone pattern C=30%, M=40%, Y=0% Interpolate in colorant amounts Color HANS Place NPs in single operation NPac vector Halftone pattern W=50%, C=20%, M=10%, Y=0%, CM=20%, CY=0%, MY=0%, CMY=0% interpolate in relative area coverage 6000 basic choices! © Copyright 2013 Hewlett-Packard Development Company, L.P. W=70%! C1=2%! M1=5%! Y1=5%! K1=6%! C1M1=1%! C1K1=2%! M1K1=3%! Y1K1=2%! C2=4%!
- 9. basics NP A pattern C, formed by combining some of a printing system’s NPs, can be characterized by its NP area coverage (NPac) vector – NPacC k – number of colorant levels / colorant / pixel n – number of colorants, (i.e., the weights are convex) ! NPi – the i-the NP T() – color (e.g., Yule-Nielsen-corrected XYZ) © Copyright 2013 Hewlett-Packard Development Company, L.P. 1/3! 2/9! 2/9! 2/9!
- 10. sociativity of convex combinations 3 Convex combination of relative area coverage weighted NP colors can also be seen as the convex combination of two constituent patterns – CA and CB, where wCi = wCBi + wCAi =! 1/3! 2/9! 2/9! 2/9! *1/3+! 1/3! 2/3! 1/9! 2/9! © Copyright 2013 Hewlett-Packard Development Company, L.P. *1/3! *2/3! 1/3! 1/3! 1/3! 2/9! 2/9! 2/9! *2/3!
- 11. consequencÑ of associativity ink! 40! area coverage! 30! lightness! Consequence of associativity: convex combinations not only of at-pixel states (i.e., Neugebauer Primaries), but also of a pattern’s sub-patterns. 50! Xn 20! 10! 0! 0! New NPacs can be constructed by convexly combining other NPacs, and this process can, in principle, go on ad infinitum. 40! Yn chroma! 60! 80! 50! area coverage (%)! • 20! C! W! 25! CM! K! M! 0! © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 12. herzog 1be shaped gamut © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 13. the eight ttern Ê printer Device RGB Interface WHITE WHITE CYAN CYAN MAGENTA BLUE YELLOW BLUE GREEN RED MAGENTA GREEN YELLOW BLACK RED BLACK Yule-Nielsen XYZ measurments of HANS NPac characterisation chart YES Print & measure NPs and NPacs © Copyright 2013 Hewlett-Packard Development Company, L.P. Select 8 vertices in correspondence with RGB cube Apply tetrahedral RGB tessellation to 8 vertices in XYZn Do tetrahedra in XYZn overlap? NO RGB-NPacXYZ LUT
- 14. experimentA setup 8-vertex HANS pipeline • 3 2 LUT with 8 NPacs at RGB cube’s vertices, tessellated by 6 tetrahedra, sharing B-W long diagonal of RGB cube HP Designjet Z6200 printer 3 8 =512 color test chart measured using printer’s embedded 45°/0° spectrophotometer under D50 • CMYK pigmented inks Color differences • 90 g/m2 HP Coated Paper substrate • © Copyright 2013 Hewlett-Packard Development Company, L.P. CIE ∆E2000s between chart’s measurements and predictions from eight RGB vertex measurements + estimate of printer’s Yule-Nielsen-modeled dot gain
- 15. © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 16. every color is convex combination of up to 4 basic patterns gamut is convex © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 17. resU lts mean = 1.59 th percentile = 3.96 95 maximum = 5.54 • Good enough for ICC profiling • Same measurements can be used for calibration • Largest inscribed convex octahedral gamut © Copyright 2013 Hewlett-Packard Development Company, L.P. 100 80 frequency Once non-linearity is characterized, color control by measuring only eight basic colorant halftone patterns 120 60 40 20 0 0 2 4 6 ∆E2000 8
- 18. the eight Pattern solution Color management Color calibration LUT: Nx2 Color separation LUT: 23 © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 19. the eight Pattern solution Color management EIGHT × print + measure + node Color calibration LUT: Nx2 Color separation LUT: 23 © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 20. con(usions HANS NPac control enables ultrasimple print color formation and control • Minimal color setup requirements → calibration & profiling from 8 measurements • Convex, ‘flat-faced’ gamut → gamut mapping • 8-node look-up table → throughput / efficiency / cost © Copyright 2013 Hewlett-Packard Development Company, L.P.
- 21. acknoWledgements Will Allen Carlos Amselem David Gaston Rafa Gimenez Jordi Sender © Copyright 2013 Hewlett-Packard Development Company, L.P. “To be honest, I would never have invented the wheel, if not for Urg’s ground-breaking theoretical work with the circle.”!
- 22. thanK ou Y © Copyright 2013 Hewlett-Packard Development Company, L.P.