Measuring CMYK Halftones: The Case for Spot Color Tone Value (SCTV) - PowerPoint PPT Presentation

Measuring CMYK Halftones: The Case for Spot Color Tone Value (SCTV) Formula Mike Strickler MSP Graphic Services 70 th Annual Technical Conference · Baltimore, MD · 2018

PROPOSAL: Current density-based TVI should gradually be replaced with ISO 20654 (SCTV) colorimetric tone curves for CMYK printing. § Benefits: § Simplified calibration of all types of devices regardless of ink and screening type § Improved correspondence between measured values and visual impression § Consistent, unambiguous curves for all colors in process control software 70 th Annual Technical Conference · Baltimore, MD · 2018

Some background … 70 th Annual Technical Conference · Baltimore, MD · 2018

Unlike CMYK: Spot color tints are usually undefined 50% Magenta (from profile) L* 80 a* 20 b* -5 50% Pantone 239 C L* ? a* ? b* ? 70 th Annual Technical Conference · Baltimore, MD · 2018

Spot color gradients can be visually very nonlinear 70 th Annual Technical Conference · Baltimore, MD · 2018

TVI varies widely among spot colors Tone ramps of 15 spot inks screened and printed identically (Courtesy John Seymour) Figure 1 - TVI mw curves of 15 randomly selected inks 70 th Annual Technical Conference · Baltimore, MD · 2018

Density measurement of spot tints can be misleading Color: Reflex Blue Tonal compression in the “cyan” range Courtesy John Seymour 70 th Annual Technical Conference · Baltimore, MD · 2018

Density v Spot Color Tone (ISO 20654) Where R is X, Y, or Z reflectance Or, 1-10 -Dt X 100 1-10 -Ds 70 th Annual Technical Conference · Baltimore, MD · 2018

Old Plot v New TVI 30 25 20 Cyan Magenta 15 Yellow Black 10 5 0 0 10 20 30 40 50 60 70 80 90 100 70 th Annual Technical Conference · Baltimore, MD · 2018

Old Plot v New SCTV 2 0 Cyan 0 10 20 30 40 50 60 70 80 90 100 Magenta -2 Yellow -4 Black -6 70 th Annual Technical Conference · Baltimore, MD · 2018

Why SCTV for CMYK? Common visual reference for calibration of all devices and inks 70 th Annual Technical Conference · Baltimore, MD · 2018

Avoidance of ambiguity in “mixed” TVI displays CMYK (TVI) + Spot Color (SCTV) Spot Color (SCTV) with correction 70 th Annual Technical Conference · Baltimore, MD · 2018

Linear SCTV as a universal target? SCTV = 0% 70 th Annual Technical Conference · Baltimore, MD · 2018

Comparison: coated substrate GRACoL2013 ISO Curve A (from profile) SCTV Linear 70 th Annual Technical Conference · Baltimore, MD · 2018

Comparison: Uncoated substrate Fogra 52 (uncoated) ISO Curve B (from profile) SCTV Linear 70 th Annual Technical Conference · Baltimore, MD · 2018

Comparison: black GRACoL 2013 ISO Curve B (from profile) SCTV Linear Fogra 52 ISO Curve C (from profile) SCTV Linear 70 th Annual Technical Conference · Baltimore, MD · 2018

For backward compatibility, simplified correction curves From SCTV to GRACoL 2013 CRPC6 1 0 Cyan 0 10 20 30 40 50 60 70 80 90 100 -1 Magenta -2 Yellow -3 Black -4 From SCTV to Fogra 52 Uncoated 6 Cyan 4 Magenta 2 Yellow 0 Black 0 10 20 30 40 50 60 70 80 90 100 70 th Annual Technical Conference · Baltimore, MD · 2018

Gray balance and tonality still OK (GRACoL 2013) ✓ 70 th Annual Technical Conference · Baltimore, MD · 2018

Gray balance and tonality still OK (Fogra 52) ✓ 70 th Annual Technical Conference · Baltimore, MD · 2018

Overall match (GRACoL) ✓ ✓ To GRACoL 2013 To “GRACoL” SCTV 70 th Annual Technical Conference · Baltimore, MD · 2018

Overall match ✓ ✓ To Fogra 52 To “Fogra 52” SCTV 70 th Annual Technical Conference · Baltimore, MD · 2018

Why not G7 as a universal calibration target? Not always visually linear! 100 100 90 90 80 80 Dye Epson Inkjet 70 70 Sublimation Press 60 60 Cyan Cyan Magenta 50 Magenta 50 Yellow Yellow Black Black 40 40 30 30 20 20 10 10 0 0 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Data courtesy of Bruce Bayne 70 th Annual Technical Conference · Baltimore, MD · 2018

Recommendations: § Establish visually linear (SCTV) tone curve for a universal calibration standard § Provide “backward compatibility” with existing reference print conditions using SCTV adjustment curve sets § Continue to rely on ICC color management for precise matching to reference print conditions 70 th Annual Technical Conference · Baltimore, MD · 2018

Thank you 70 th Annual Technical Conference · Baltimore, MD · 2018