Printing aims based on a shared neutral gray-scale The relationship between CGATS TR015, the CGATS 21 data sets, and the G7 methodology David Q McDowell
What to include? The beginning of printing standards The migration from density and dot gain to colorimetry The struggle between ISO 12647, neutral gray scale, and characterization data Where were are today
In the beginning Late 60 s to Early 70 s SWOP and some Gravure packaging standards SWOP A press proofing standard Based on web offset publications Specific paper Density of the solids Dot gain of C, M, and Y and mid-tone spread
In the beginning Early to Mid 1980 s 1979-80 First digital prepress systems announced First digital data and beginning of data exchange (DDES, TIFF/IT) CGATS IT8 Committee created Late 1980 s Introduced concept of proofing to Manufacture's Application Data Sheet Proofing colorants were different than ink colors. Density did not work.
The middle years (Late 80 s-90 s) ANSI IT8 developed IT8-7/3 target Committee for Graphic Arts Technologies Standards (CGATS) created GA Color measurement standards created (CGATS.5) SWOP characterized with TR001 ISO TC130 re-established. ISO 12647 replaced density with colorimetry for aims of solids and substrate SWOP proof comparisons moved to quality of match to TR001 PDF announced
The middle years (Cont d) Characterization data introduced for other processes such as CRACoL, SNAP Color management emerged and ICC created Digital creation of printing form became reality Direct to film Direct to plate Concept of family of reference printing conditions introduced IT8.7/4 target created to merge work of FTA, ECI, and CGATS (Became ISO 12642-2)
2000 to now PDF/X introduced Digital data dominant Characterization data dominant for most work except ISO 12647 Concept of using Tone Reproduction aims introduced in US. Concept of substrate correction introduced in CGATS and ISO TC130 to correct for black vs white backing ISO 10128 published
ISO TR 10128 Attempt to define how to use characterization data and printing aims. Adjust printing such that aim one and two color solids are met. Print test form Evaluate relationship of overprint colors between characterization data and press test Adjust input data using: Single color TVIs 3-color neutral scale (via TVIs) Color management
ISO TR 10128 Also Introduced relationship between colorimetric and densitometric TVI For black ink, CIE Y matched visual density For magenta ink, CIE Y produces TVI very close to those from green density values For yellow ink, CIE Z produces TVI very close to those from blue density values For cyan ink, CIE X in combination with CIE Z produces results very close to those from red density values
Mid 2000s IDEAlliance gray balance concept introduced Backing correction evolved to become substrate correction SWOP, GRACoL, and other characterization data sets created based on prior aims for solids and using neutral gray balance aims. IDEAlliance G7 program created to provide computational and consulting support for gray balance approach to printing.
Mid 2000s IDEAlliance G7 program pushed printing to gray balance aims assuming that since characterization data was based on gray balance appearance of printed sheets would match. Proofing system validation was still based on characterization data European s (led by Germany) were pushing ISO 12647 printing aims (solids & TVI) US was moving to printing to characterization data and/or gray balance.
The struggle within the US The IDEAlliance G7 approach puts emphasis on tone reproduction of a neutral scale defined in terms of CMY triplets and substrate adjusted colorimetry. Solids are essentially left to user or others to define Aim tone reproduction (TR) curve(s) puts emphasis on keeping substrate to midtone TR curve as constant as possible based on the assumption that if highlight TR is consistent visual appearance will also be consistent.
The struggle within the US Characterization data defines relationship between CMYK data and printed color for a specific printing condition. Substrate correction has been introduced to allow all colorimetric data to be adjusted to approximate the changes resulting from a change in substrate COLOR. Includes (directly or indirectly) aims for solids, process control parameters, neutral scale etc. With modern color management tools characterization data should be essentially process independent.
CGATS TR 015 Defines and mathematically documents: The CMY triplets that form the neutral scale The aim CIE L* values of the 3-color neutral scale relative to input cyan TV as a function of substrate L* and L* of 3-color solid The aim CIE L* values of the K scale vs input K TV as a function of substrate and solid L*. The substrate corrected aim CIE a* and b* values of the neutral scale
Predefined 3-color neutral M = Y = 0.747 C 4.1x10-4 C 2 + 2.94x10-5 C 3 Typical Values C M/Y 25 18.9 40 31.1 50 40.0 60 49.7 75 66.1 90 85.3
Neutral Print Densities 1.80 1.60 Neutral Print Density 1.40 1.20 1.00 0.80 0.60 0.40 0.20 CRPC 1 CRPC 2 CRPC 3 CRPC 4 CRPC 5 CRPC 6 CRPC 7 0.00 0 10 20 30 40 50 60 70 80 90 100 Input Tone value (Cyan)
Substrate relative tone reproduction 100 90 80 Substrate Relative L* 70 60 50 40 30 CRPC 1 CRPC 2 CRPC 3 CRPC 4 CRPC 5 CRPC 6 CRPC 7 20 10 0 0 20 40 60 80 100 Input Tone Value (Cyan)
L* vs Input tone value (Cyan) 100 90 80 3-color Neutral Scale L* 70 60 50 40 30 CRPC 1 CRPC 2 CRPC 3 CRPC 4 CRPC 5 CRPC 6 CRPC 7 20 10 0 0 20 40 60 80 100 Input Tone Value (Cyan)
Aim a* b* values 6 4 a* b* for Substrate of a* = 5, b*=-7 2 0-2 a* b* -4-6 -8 0 10 20 30 40 50 60 70 80 90 100 Input Tone value (Cyan)
CGATS 21 Family of characterization data sets covering the printing gamuts from newsprint through an extra large gamut. Solids based on ISO 12647 aims as much as possible Neutral scale and tone reproduction based on CGATS TR 015 Substrate correction explicitly included Within each data set the C, M, and Y density equivalent TVI curves have the same value ISO TR 10128 included by reference
Data set creation goals The data sets for DIS15339, and its US counterpart CGATS.21, were created with the following goals: 1. Adjust the primary and two-color solid aims to be as consistent as possible colorant descriptions documented in DIS12647-3 and DIS12647-2. 2. Maintain CMY and K neutral scales that are consistent with CGATS TR015. 3. Adjust colorimetric TVI of primary tone scales to align with selected TVI curves documented in DIS12647-3 and DIS12647-2. Colorimetric TVI is calculated according to ISO TS10128, Annex A.
CGATS 21-2 CRPC Data Sets 1 Universal ColdsetNews Small gamut printing (newsprint) 2 Universal HeatsetNews Moderate gamut printing on improved newsprint type paper 3 Universal PremUncoated Utility printing on matt uncoated type paper 4 Universal SuperCal General printing on supercalendared paper 5 Universal PubCoated Typical publication printing 6 Universal PremCoated Large gamut (typically commercial) printing 7 Universal Extra Large Extra large gamut printing processes
CGATS 21-2 CRPC Data Sets
Comparison Table, 1- & 2- Color Solids CRPC Reference DE2000 Max Paper DE2000 1 ISO DIS 12647-3 0.9 0.0 2 ISO DIS 12647-2 CD1 2.0 1.3 3 ISO DIS 12647-2 CD5 1.1 0.0 4 ISO DIS 12647-2 CD6 1.9 0.6 5 ISO DIS 12647-2 CD2 1.8 1.2 6 ISO DIS 12647-2 CD1 1.3 0.0
Comparison Table, vs FOGRA/IFRA CRPC Reference DE2000 Max 1 IFRA 26 0.9 2 FOGRA 48 1.8 3 FOGRA 47 1.5 4 FOGRA 40 1.3 5 FOGRA 45 1.8 6 FOGRA39 1.5
The future CGATS 21 presents a merger and compromise ISO 12747 used as aims for solids and overprints TR015 used as the basis for neutral scale aims and tone reproduction Substrate correction used to adjust for changes in substrate Process control procedures can be based on TR015 or G7 or ISO 10128
Where now CGATS 21-1 and CGATS 21-2 published CGATS 21 will be the basis for US printing certification CGATS 21 started in response to TC130 opposition to similar proposal as ISO 15339 Using CGATS 21 as the basis, a new draft of ISO 15339 will be offered in the upcoming TC130 meeting
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