RGB inks in a CMYK world
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Invited talk given at Fogra Colour Management Symposium on 26th February 2010 in Munich, Germany.
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RGB inks in a CMYK world
- 1. RGB inks in a CMYK world Dr. Ján Morovič Hewlett–Packard Company Fogra Colour Management Symposium 26th February 2010, München 2010 © Hewlett–Packard Company
- 2. Overview Background CMY and CMYK printing Potential benefits of multi–primary printing Challenges of using multiple primaries Conclusions 2010 © Hewlett–Packard Company
- 3. What is multi–primary printing? 2010 © Hewlett–Packard Company
- 4. Terminology primary – a colorant (ink, toner, dye, wax, ...) chromatic primary – primary with significant colorfulness as opposed to a neutral, achromatic primary secondary – the result of using two primaries simultaneously e.g. cyan and yellow, giving a green result multi-primary – using more than three/four primaries (cyan, magenta, yellow + black) 2010 © Hewlett–Packard Company
- 5. Background 2010 © Hewlett–Packard Company
- 6. Digital printing on the up move from B&W to CMYK+ 2007: CMYK+ 45%; multi-primary 10% 2015: CMYK+ 75%; multi-primary 15% growth of WW digital print market 2005: €32 billion 2015: €125 billion strong benefits for customers (differentiation, flexibility) and print service providers (value added, cost) market share highly desirable 2010 © Hewlett–Packard Company
- 7. HP portfolio HP Professional Displays HP Photosmart Pro Printers HP LF Design Printers HP LF Commercial Printers HP DreamColor LP2480zx HP Photosmart Pro B9180 Printer HP Designjet Z3200 HP Designjet L65500 Printer series Professional Display Photo Printer series HP LF Industrial Printers HP Light Production MFP HP Indigo Digital Presses HP Scitex TJ8300/TJ8500 Printer series HP CM 8000 Series Color MFP HP Indigo 7000 Digital Press HP Web Press HP SmartStream Workflows 2010 © Hewlett–Packard Company
- 8. CMY printing 2010 © Hewlett–Packard Company
- 9. The simplicity of CMY ideal CMY primaries – each controls one of eyeʼs color receptor (cone) types e.g., changing amount of cyan (C): changes amount of light absorbed in low–frequency part of visible electromagnetic spectrum L cone is sensitive to it – response controlled by C each color can be matched using exactly one CMY combination 2010 © Hewlett–Packard Company
- 10. 2010 © Hewlett–Packard Company
- 11. Color inputs to ink amounts 2010 © Hewlett–Packard Company
- 12. CMY limitations unwanted stimulations cone sensitivities overlap trichromatic methods cannot match all color experiences e.g., C affects not only L cones but also M and S ones printing black text or line art using CMY can result in artifacts from miss–registration unwanted absorptions actual inks are not like ideal ʻblock dyesʼ – further gamut drop poor color constancy prints change appearance with illumination 2010 © Hewlett–Packard Company
- 13. CMY limitations 2010 © Hewlett–Packard Company
- 14. CMYK printing 2010 © Hewlett–Packard Company
- 15. What can adding blacK do? increase lightness range printing black line art and text using single ink lower cost amounts of more expensive CMY inks replaced by smaller amount of cheaper K ink improve color constancy using more K (spectrally flat) gives prints that change less with changes in lighting 2010 © Hewlett–Packard Company
- 16. What can adding blacK do? increase lightness range printing black line art and text using single ink lower cost amounts of more expensive CMY inks replaced by smaller amount of cheaper K ink improve color constancy using more K (spectrally flat) gives prints that change less with changes in lighting 2010 © Hewlett–Packard Company
- 17. What can adding blacK do? increase lightness range printing black line art and text using single ink lower cost metameric amounts of more expensive CMY inks replaced by color inconstant smaller amount of cheaper K ink improve color constancy using more K (spectrally flat) gives prints that change less with changes in lighting 2010 © Hewlett–Packard Company
- 18. Color inputs to ink amounts 2010 © Hewlett–Packard Company
- 19. Cost of adding K redundancy same color can be achieved using multiple, alternative primary combinations – e.g. K=10 and C=M=Y=10 may be equivalent trade-offs K=10 is cheaper and more color constant; C=M=Y=10 is less grainy consequences identify which print attributes matter – use primaries appropriately balance likely to depend on application – in photography grain is more objectionable than in technical illustrations 2010 © Hewlett–Packard Company
- 20. Multi–primary benefits 2010 © Hewlett–Packard Company
- 21. More gamut most obvious benefit adding carefully chosen new inks to CMY allows for reduction of unwanted absorptions therefore spectra that allow for greater cone response ratios therefore greater resulting colorfulness e.g., adding red, green and blue inks to CMY can increase color gamut on a given paper by a quarter 2010 © Hewlett–Packard Company
- 22. 2010 © Hewlett–Packard Company
- 23. Prolonged lightfastness colorfulness and longevity are natural enemies some materials tend to have greater gamut at expense of longevity some dyes versus more lightfast but less colorful pigments trade-off is most marked at same number of primaries though → adding more primaries can deliver both attributes e.g. gamut of six primary dye printer can be matched by ten primary pigment printer, which has far greater longevity 2010 © Hewlett–Packard Company
- 24. Prolonged lightfastness 2010 © Hewlett–Packard Company
- 25. Prolonged lightfastness 2010 © Hewlett–Packard Company
- 26. Other benefits Better color constancy: colorants resulting in ʻflatterʼ spectra are used Less grain: colorants with more similar density / lightness are combined Spectral reproduction: match under wider range of illumination enabled by greater spectral gamut Reduced ink volume: primaries close to traditional secondaries e.g. M=Y=10 can be replaced by R=10 in hypothetical printer – halving the ink amount; 15% overall saving typical Küppers side–by–side printing: enabling opaque inks, lower ink use, greater predictability (e.g., Océ CPS700 printer) 2010 © Hewlett–Packard Company
- 27. Challenges 2010 © Hewlett–Packard Company
- 28. Color inputs to ink amounts 2010 © Hewlett–Packard Company
- 29. Multi–primary color gamut determining color gamut of 12 ink printer requires sampling 12 dimensional space coarse, uniform sampling of 10 steps per colorant – 1 trillion primary combinations predicting the color of each of these combinations – decades of computation gamut is needed when: designing and choosing primaries color separations are developed for them 2010 © Hewlett–Packard Company
- 30. Twisting transitions 2010 © Hewlett–Packard Company
- 31. Sneaky secondaries 2010 © Hewlett–Packard Company
- 32. Sneaky secondaries Y+R=R M+B concave 2010 © Hewlett–Packard Company
- 33. Spectral gamut mapping when spectral reproduction is the aim, what is done for spectra that cannot be matched – spectral gamut mapping understanding still in infancy most popular approach (e.g. Chau & Cowan, 1996): represent spectra in 3+n dimensional space (Wyszecki, 1953) first three account for colorimetry under chosen light source – ʻfundamental basesʼ remaining are ʻmetameric blacksʼ - only account for spectral and not colorimetric properties match original in fundamental bases minimize distance in metameric blacks 2010 © Hewlett–Packard Company
- 34. fundamental bases original reflectance all metamers single set of all possible black weights + black weights metameric blacks P. Morovič ʼ07 2010 © Hewlett–Packard Company
- 35. Other challenges Amplitude modulated halftoning: moiré Colorant capacity: same limit applies for all ink sets – only combinations below it are valid $%&%'()*%$!+,!-./.')(%&')-!0*$!-.1&!-')&%')02!! ! Chen ’06 Figure 3–8. Portion of the target used for detecting inkblots. Table 3-6. Summary of digital signal and effective area coverage of all the overprint 2010 © Hewlett–Packard Company
- 36. RGB and CMYK access n–primary systems most directly addressed via n channels but, there is need for RGB and CMYK interfaces to multi–primary systems: ease of integration vast majority of content defined in three dimensions (RGB or CMYK with a specific black generation) challenge: design virtual RGB and CMYK spaces for addressing multi-primary system the two also need to be consistent with each other 2010 © Hewlett–Packard Company
- 37. Self–calibration and profiling complex, multi–primary printing systems benefit from embedded spectral reflectance measurement self–calibration and profiling result in more stable and predictable output easier and faster integration of printer into existing workflows greater flexibility of using them to print onto wider range of substrates 2010 © Hewlett–Packard Company
- 38. Conclusions 2010 © Hewlett–Packard Company
- 39. Futurology • Move towards more primaries in production (benefits seen in photo & fine art + potential for new benefits) • Move towards some spectral reproduction (but not across the board – colorimetric originals need no spectral reproduction) • Cost likely to be strong driver (but at increasing image quality) • Commoditization of color gamut (with differentiation in others; underlining importance of standardization) 2010 © Hewlett–Packard Company
- 40. Conclusions 1. multi–primary printing has potential to deliver more value both to its providers and recipients and is on the increase 2. having more than three chromatic inks opens door to host of benefits (gamut, constancy, spectral reproduction, grain, ink volume, non–overprinting) 3. delivering potential benefits is not low hanging fruit but requires tackling currently unsolved problems 2010 © Hewlett–Packard Company
- 41. Acknowledgments Michel Encrenaz Johan Lammens Albert Serra Rafa Gimenez Jordi Arnabat Aleix Oriol Virginia Palacios Ramon Pastor Marti Maria Peter Morovič Jay Gondek Eduard Garcia Xavi Bruch 2010 © Hewlett–Packard Company
- 42. Thank you! 2010 © Hewlett–Packard Company