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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

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70th Annual Technical Conference · Baltimore, MD · 2018

Measuring CMYK Halftones: The Case for Spot Color Tone Value (SCTV) Formula

Mike Strickler MSP Graphic Services

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70th Annual Technical Conference · Baltimore, MD · 2018

§ 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

PROPOSAL: Current density-based TVI should gradually be replaced with ISO 20654 (SCTV) colorimetric tone curves for CMYK printing.

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70th Annual Technical Conference · Baltimore, MD · 2018

Some background …

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70th Annual Technical Conference · Baltimore, MD · 2018

L* 80 a* 20 b* -5

Unlike CMYK: Spot color tints are usually undefined

50% Magenta (from profile) L* ? a* ? b* ? 50% Pantone 239 C

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70th Annual Technical Conference · Baltimore, MD · 2018

Spot color gradients can be visually very nonlinear

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70th Annual Technical Conference · Baltimore, MD · 2018

TVI varies widely among spot colors

Figure 1 - TVImw curves of 15 randomly selected inks

Tone ramps of 15 spot inks screened and printed identically (Courtesy John Seymour)

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70th 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

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70th Annual Technical Conference · Baltimore, MD · 2018

Or, 1-10-Dt 1-10-Ds

Density v Spot Color Tone (ISO 20654)

Where R is X, Y, or Z reflectance

X 100

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70th Annual Technical Conference · Baltimore, MD · 2018

Old Plot v New

TVI

5 10 15 20 25 30 10 20 30 40 50 60 70 80 90 100 Cyan Magenta Yellow Black

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70th Annual Technical Conference · Baltimore, MD · 2018

Old Plot v New

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2 10 20 30 40 50 60 70 80 90 100 Cyan Magenta Yellow Black

SCTV

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70th Annual Technical Conference · Baltimore, MD · 2018

Why SCTV for CMYK?

Common visual reference for calibration of all devices and inks

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70th Annual Technical Conference · Baltimore, MD · 2018

Avoidance of ambiguity in “mixed” TVI displays

CMYK (TVI) + Spot Color (SCTV) Spot Color (SCTV) with correction

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70th Annual Technical Conference · Baltimore, MD · 2018

Linear SCTV as a universal target?

SCTV = 0%

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70th Annual Technical Conference · Baltimore, MD · 2018

Comparison: coated substrate

GRACoL2013 ISO Curve A (from profile) SCTV Linear

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70th Annual Technical Conference · Baltimore, MD · 2018

Fogra 52 (uncoated) ISO Curve B (from profile) SCTV Linear

Comparison: Uncoated substrate

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70th 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

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70th Annual Technical Conference · Baltimore, MD · 2018

For backward compatibility, simplified correction curves

2 4 6 10 20 30 40 50 60 70 80 90 100 Cyan Magenta Yellow Black

From SCTV to GRACoL 2013 CRPC6 From SCTV to Fogra 52 Uncoated

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1 10 20 30 40 50 60 70 80 90 100 Cyan Magenta Yellow Black

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70th Annual Technical Conference · Baltimore, MD · 2018

Gray balance and tonality still OK (GRACoL 2013)

✓

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70th Annual Technical Conference · Baltimore, MD · 2018

Gray balance and tonality still OK (Fogra 52)

✓

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70th Annual Technical Conference · Baltimore, MD · 2018

Overall match (GRACoL)

To GRACoL 2013 To “GRACoL” SCTV

✓ ✓

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70th Annual Technical Conference · Baltimore, MD · 2018

Overall match

To Fogra 52 To “Fogra 52” SCTV

✓ ✓

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70th Annual Technical Conference · Baltimore, MD · 2018

Not always visually linear!

Why not G7 as a universal calibration target?

Epson Inkjet

10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 Cyan Magenta Yellow Black 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 Cyan Magenta Yellow Black

Dye Sublimation Press

Data courtesy of Bruce Bayne

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70th Annual Technical Conference · Baltimore, MD · 2018

§ 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

Recommendations:

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70th Annual Technical Conference · Baltimore, MD · 2018

Thank you