The Standard Is Not the Measurement

Ronen Dolev | Industrial Color Engineering Series | October 2026

The report says PASS. Which reference did it actually test?

A brand owner receives three production samples: a folding carton, a pressure-sensitive label, and a flexible pouch. The samples were manufactured on different printing routes, and each color report declares an acceptable result. Quality signs off the jobs. But the customer asks for the reports to be consolidated into one international acceptance record, and the problem becomes visible: one job was verified against a legacy coated-paper characterization, another against a newer coated-paper reference, and the third against a locally maintained digital target. The measurement instruments may also have used different M settings.

A familiar multi-site digital case illustrates the problem: three independently governed production routes can use M1, M0, and M2 while each reports an acceptable result. Here, the same diagnostic principle applies to a broader, explicitly cross-technology setting involving digital, offset, and flexographic production. The scenario is educational; it is not a claim that a particular customer or press survey was conducted.

The mistake is not that M0, M1, or M2 are inherently "bad." The mistake is assuming that results produced under different measurement conditions and evaluated against different target definitions can be collected into a common PASS column without first reconciling their meaning.

That is the question this article answers: Which measurement procedure belongs with which approved reference, which printing condition is the job meant to simulate, and what does G7 actually prove?

Four categories that must never be collapsed into one label

Production teams frequently use the word "standard" for several different layers of control. ISO 13655 governs spectral measurement and related colorimetric computation. ISO 3664 governs standardized viewing conditions. A FOGRA characterization set or a GRACoL/CRPC dataset identifies a particular reference printing appearance or dataset. G7 (and its successor, G7+) concerns aligning gray balance and neutral tonality, not selecting a specific paper reference. Fogra ProcessStandard Digital (PSD) is a process-control framework for digital print stability, verification, and workflow discipline.

These objects are not interchangeable. A digital press can be calibrated through a G7 workflow, characterized with its own media-specific profile, and asked to simulate GRACoL 2013/CRPC6. It could instead be assigned a FOGRA51 appearance aim if that is the customer's accepted contract reference. The printing mechanism does not change to offset merely because the digital output aims at an offset-derived reference.

The five-part reference chain. A defensible color report starts by identifying the approved source: the brand color or CMYK reference. It then names the exact characterization dataset, such as FOGRA51, FOGRA52, or GRACoL 2013/CRPC6. Next come the measurement conditions, including the M setting, backing, geometry, and aperture. Production must then be stabilized and controlled with the appropriate calibration or process framework. Only at the end should the finished physical product be compared with the agreed proof. A correct result at any one stage does not replace the other four.

Saying a device is "calibrated to FOGRA" is incomplete. Which FOGRA characterization number? For what substrate? In which measurement condition? Is the route reproducing a reference appearance, or is the press operating under the offset process itself? Where is the contract proof? Is the customer asking for a printed-sheet measurement, a laminated pouch, or an applied label? The right answer begins by identifying the specific color-data chain.

M0, M1 and M2: conditions, not levels of quality

ISO 13655:2017 remains the relevant published international standard for graphic-arts spectral measurement. M0 describes a legacy measurement condition for which UV behavior is not controlled to the M1 D50-related requirement. M1 specifies a D50-related measurement condition and is especially important when fluorescent optical brightening agents (OBAs) may affect the substrate white and printed colors. M2 is the UV-cut condition, used to suppress most UV-related fluorescent excitation during measurement. M3 is also a polarized condition for applications such as certain density/control tasks, but it is not a routine replacement for M1 or M2 color comparison.

A familiar source of error is an operator who changes a device to M2 during a justified diagnostic investigation, then leaves it there. The next job may be checked against a reference whose target data were defined in M1. The instrument still reports precise and repeatable Lab values. The comparison has lost its agreed basis.

This is especially serious on OBA-containing papers and folding boards, since brighteners absorb UV and re-emit visible light, often in the blue region. On a film with little fluorescence, the difference between M1 and M2 may be small; on another substrate it may be consequential. There is no universal numerical "M1-to-M2 correction" that can be applied indiscriminately across papers and printed constructions.

How the same sheet can yield different color readings. Imagine one paper with optical brightening agents measured three ways. M0 follows a legacy measurement condition without the M1-controlled UV specification. M1 uses a D50-related measurement condition that accounts for the relevant fluorescent response. M2 suppresses the UV contribution. The instrument can report three different apparent whites even though the paper underwent no physical change. This is a conceptual example, not an instrument reading, and the magnitude and direction depend on the stock, the equipment, and its optical behavior.

A correct report must state the M condition, illuminant/observer used for computed coordinates, aperture and measurement geometry (where relevant), backing, sample condition, instrument identity (where traceability requires it), and the target-dataset version. If a control strip was measured before varnishing but the approved appearance is post-varnish, the measurement may be valid for process monitoring but not sufficient for final-product release.

What does ISO 3664:2025 change for the viewing booth?

The 2025 edition of ISO 3664 defines viewing conditions for reflection and transmission print applications. In addition to P1/P2, it introduces P3/P4 conditions that support viewing under D50-related illumination without the UV contribution relevant to optical brighteners. The useful correspondence is conditional: M1 measurements align with P1/P2 viewing; M2 measurements align with P3/P4 when such low-UV evaluation is appropriate.

This is not permission to replace M1 with M2 whenever a customer mentions LED lighting. A reference condition remains tied to the measurement method used to establish it. For a job contractually specified against an M1 dataset, switching the production measurement to M2 without a newly agreed target changes the basis of the comparison. The intended use environment may justify additional low-UV evaluation or a separately agreed specification, but not silent substitution.

Similarly, a booth labeled D50 should not be assumed equivalent to every LED in a supermarket. Two LEDs with the same nominal correlated color temperature can have different spectral energy distributions. The difference matters when brighteners or metameric ink pairs are present. Viewing-condition alignment is essential, but it does not replace the separate examination of ink spectra, gloss and finished-object construction.

Which FOGRA reference is the correct one?

FOGRA is an organization producing multiple characterization datasets for different printing conditions. A higher FOGRA number is not a quality score and does not automatically supersede all earlier datasets for every purpose. The choice is driven by the intended reference printing condition, the substrate class, and the customer's source files and proofing contract.

FOGRA39 is the well-known legacy coated-paper characterization associated with ISO Coated v2. It belongs to an older reference environment in which M0 measurement history is common. Files and customer-approved legacy proofs may still refer to this dataset. That historical relevance is not a reason to relabel FOGRA39 data as FOGRA51 data.

FOGRA51, associated with PSO Coated v3, represents a newer coated-paper reference condition and uses a contemporary, M1-oriented workflow. FOGRA52, associated with PSO Uncoated v3, describes a distinct uncoated, OBA-containing stock condition, also with M1. FOGRA52 is not simply "FOGRA51 without gloss." The substrate white, printed gamut, tone behavior, and reference data differ.

FOGRA also maintains other datasets, including characterization conditions for finished laminations and exchange spaces. A file with a FOGRA number does not remove the need to check its actual application. In particular, FOGRA55 describes an expanded-gamut exchange space; its existence does not mean a specific digital or flexographic press automatically conforms to a seven-color offset production condition.

Match the reference before evaluating a result. FOGRA39 belongs to a legacy coated-paper reference and its original dataset, commonly associated with historical M0 workflows. FOGRA51 is the M1-oriented PSO Coated v3 reference. FOGRA52 is the distinct M1-oriented PSO Uncoated v3 reference. GRACoL 2013/CRPC6 is a separate M1 reference appearance that other printing technologies may simulate. G7 and G7+ describe neutral-tone alignment methods, not a substitute substrate characterization dataset. None of these labels should be exchanged merely because a report shows similar Lab numbers.

Decision example: coated carton versus uncoated insert

A coated folding carton has a contract target of PSO Coated v3 / FOGRA51. Its control print is measured with M1 against the corresponding dataset. The same customer also orders an uncoated leaflet. Printing the leaflet and comparing its CMYK solids directly to FOGRA51 does not validate an uncoated condition. If the contract specifies PSO Uncoated v3, the correct corresponding characterization is FOGRA52, with an M1-based measurement workflow and substrate-appropriate validation. Two different references can still belong to one visually governed product family. A single dataset cannot be imposed on all paper surfaces merely for spreadsheet convenience.

GRACoL: a reference printing appearance that digital can simulate

GRACoL (General Requirements for Applications in Commercial Offset Lithography), in its GRACoL 2013 form, is widely used for color-data exchange, proofing and reference print appearance. GRACoL 2013 coated is commonly associated with CRPC6, one of the characterized reference printing conditions in ISO/PAS 15339-2 / CGATS 21. The dataset is based on M1 measurement. It is applicable as a source/reference aim for a variety of CMYK imaging processes, including digital output that aims to reproduce the specified reference appearance.

The correct statement for a digital printer is therefore not "our LEP press is an offset press because it prints GRACoL." The correct statement is "our digital press is calibrated, characterized and controlled to simulate the GRACoL 2013/CRPC6 reference within the agreed criteria and finished output condition."

GRACoL2013/CRPC6 and PSO Coated v3/FOGRA51 are related but distinct reference datasets. They should not be treated as identical without deliberate cross-reference assessment. A proof approved against one data condition cannot be automatically relabelled as conformity to the other.

The North American reference system also includes uncoated and other CRPC classifications. Use the relevant declared dataset rather than applying the common "GRACoL 2013 coated" profile to an uncoated stock because the file happened to be available in the RIP.

Where G7 fits — and where it does not

G7 was developed as a calibration approach that emphasizes near-neutral appearance, gray balance, and tonality. It is a powerful framework for aligning CMYK reproduction across printing systems. However, a G7-calibrated press is not, by that fact alone, a verified match to every GRACoL, FOGRA, spot-color, or finished-packaging reference.

For example, a press can obtain neutral ramps with good gray balance and still reproduce one saturated red or blue outside the target's tolerance. Neutral tonality does not define the entire gamut, the source profile, the substrate white, or the spectral response of spot ink. Conversely, a digital press can aim at a FOGRA reference while a suitable G7 method provides part of its neutral calibration strategy. These functions coexist rather than compete.

G7+ is the more recent development, extending the methodology to a wider range of ink densities, substrates, and technologies. As of 2026, PRINTING United Alliance describes improved tone/gray alignment and additional high-density smoothing features. It should be named when that is the actual qualified method; do not automatically rewrite historic G7 records as G7+ compliance.

What a neutral ramp does—and does not—prove. Imagine a sequence of patches from a pale neutral through midtones to a dark neutral. Before calibration, the nominally gray progression might carry a subtle violet or blue cast; after effective neutral-tone alignment, it may appear more consistently gray. That demonstrates one aspect of tonal control. It does not prove that the full color gamut, a specific spot color, a particular substrate white, or a finished package matches its declared reference. This is a conceptual description, not a measured G7 verification result.

Where ProcessStandard Digital belongs

Fogra's ProcessStandard Digital (PSD) is a discipline for digital output quality, process stability, color accuracy, and workflow consistency. Its certification approach uses defined tasks, test forms, and verification methods, including a selected reference condition where appropriate. PSD does not require a digital printing mechanism to become physically identical to offset. It gives the printer a framework for delivering controlled output against declared aims.

A useful production sequence is: confirm press and media stability; calibrate using the appropriate platform method; characterize the stable condition; select or confirm the correct output target; verify representative printed patches against the correct dataset under the prescribed measurement condition; and repeat the check after relevant finishing. Rebuilding an ICC profile during substrate or transfer instability simply creates a more sophisticated description of a drifting system.

Choosing the correct reference: practical decisions

The following examples are workflow guidance rather than replacements for licensed standards or current characterization files. The expected measurement basis refers to the published or commonly associated reference-data condition; project-specific requirements must still be verified.

FOGRA39 / ISO Coated v2 legacy. Comparison basis: Original dataset; historically M0 workflow. Avoid: Comparing directly to FOGRA51 M1 and calling both the same target.

FOGRA51 / PSO Coated v3. Comparison basis: Correct FOGRA51 M1 reference data. Avoid: Using M2 on an OBA board against M1 targets.

FOGRA52 / PSO Uncoated v3. Comparison basis: Correct FOGRA52 M1 reference data. Avoid: Treating FOGRA51 as an uncoated-paper target.

GRACoL 2013 / CRPC6. Comparison basis: GRACoL 2013/CRPC6 M1 data. Avoid: Assuming G7 calibration alone proves CRPC6 conformity.

Customer-defined spectral brand spot. Comparison basis: Approved spot source + qualified M/geometry/backing. Avoid: Treating Lab values without the source method as universal.

G7 or G7+ calibration project. Comparison basis: Version-specific neutral/tone verification procedure. Avoid: Reporting G7 as if it were a FOGRA/GRACoL dataset.

Digital process-control verification. Comparison basis: Selected reference + approved PSD verification protocol. Avoid: Confusing process stability with universal cross-media color identity.

The subtle false-pass problem

Suppose a production print is measured in M2 and its Lab values look close to a manually copied spreadsheet target originally generated from M1 measurement on a fluorescent board. The apparent PASS is not sufficient evidence of conformity: the measurement and reference are not defined under the same method. The error can hide in either direction. It is possible to declare a false failure of acceptable print or a false pass of unacceptable print. The exact magnitude and direction depend on the substrate, ink, fluorescence, and measurement setup; invented numerical corrections would be inappropriate.

The justifiable M2 project

Now consider a separate product designed primarily for low-UV indoor viewing. The customer and technical team deliberately establish a low-UV evaluation specification with an appropriately defined M2 source and corresponding P3/P4 viewing process. M2 is correct within that project. It becomes incorrect only when somebody quietly compares those readings against M1 reference data as if they described the same measurement basis.

Two distinct failures: reference governance and spectral mismatch

Two different technical failures can look similar on an approval report. In one, different formulations yield close CIELAB values but have different spectral reflectance responses, and the substrate, transparency, or finish may change the approved appearance. In the other, separately controlled digital production routes drift into incompatible measurement and target-governance settings. The first requires spectral and physical investigation; the second first requires a common and traceable measurement-reference chain. Neither is solved reliably by altering a color recipe before defining the failure.

These failure modes must remain separate. A mismatch between the declared target and the measurement method is a governance error. A demonstrated illuminant-dependent separation of different colorant constructions is a spectral behavior problem. This article focuses on establishing the correct reference first so that subsequent measurements can be interpreted honestly.

An audit card for digital, offset and flexographic production

A cross-technology color report should identify the approved reference by full name and version; distinguish source from destination profiles; list the instrument, M mode, geometry, aperture and backing; specify sample state (uncoated web, varnished carton, laminated pouch, applied label); record which illuminant and observer apply to computed Lab values; identify the ΔE formula and declared tolerance; and retain a physical reference and measured verification patch set.

For digital printing, also capture the press/media calibration state, characterization version, ICC and DFE job settings. For offset, capture the print condition, ink/spot formulation, and relevant TVI and finishing settings. For flexography, capture the ink system, anilox, substrate, ink-transfer state, and, where relevant, the finished laminate. No report is reliable simply because a single green PASS badge appears on screen.

The reference-and-measurement decision path. Start by selecting the exact characterization dataset and version. Verify that the reference applies to the intended substrate and print condition, and that the instrument M setting and backing are compatible. Independently confirm press calibration and production stability; align viewing to the agreed reference and any justified additional low-UV evaluation. Only then measure the finished carton, laminated pouch or applied label against the same declared target. If one condition is inconsistent, correct the procedure before issuing a PASS or changing the ink.

Troubleshooting: when "the standard" means different things

One site says FOGRA, another says GRACoL. Possible error: Different source/reference condition. First action: Name datasets and versions; obtain contract proof.

The same press passes M2 but fails M1 on a bright board. Possible error: Fluorescence / wrong comparison basis. First action: Check agreed target M mode and OBA effect.

The digital proof simulates FOGRA51; the offset sample uses FOGRA39. Possible error: Legacy versus new reference mixed. First action: Rebuild comparison under one declared source.

G7 gray is neutral, but brand spot fails. Possible error: G7 is not a spot-color target. First action: Assess gamut, channel recipe, and spot reference.

Uncoated sample compared against coated profile. Possible error: Wrong substrate/printing condition. First action: Use correct FOGRA52 or applicable specified aim.

GRACoL profile applied to all media. Possible error: Source profile mistaken for destination process. First action: Profile each stable device/media output condition.

Prints match M1 but differ in low-UV retail light. Possible error: Viewing and fluorescence / spectral interaction. First action: Assess P3/P4 and product use separately.

Two instruments report different Lab for same print. Possible error: Method or inter-instrument agreement. First action: Check calibration, backing, geometry, M condition.

Color shifts after varnish or laminate. Possible error: Wrong sample release point. First action: Compare and qualify completed construction.

PSD results are good, but the brand family looks inconsistent. Possible error: Process control is not global brand identity. First action: Review governed physical master and application.

A robust release procedure in eight actions

1. Identify the exact source/reference characterization dataset and the customer-approved physical proof; do not use a reference name without version.
2. Confirm that the selected dataset is appropriate for the intended substrate, print condition, and contract.
3. Match instrument settings to that dataset or to a specifically authorized alternative method; never silently convert M1 results to M2 targets.
4. Verify viewing conditions and decide whether UV-rich or low-UV use environments require separate assessment.
5. Stabilize and calibrate each production route; apply G7/G7+ or platform-specific methodology where specified.
6. Characterize the stable device/media system, use an appropriate destination profile, and preserve DFE/RIP conversion settings.
7. Verify production against the declared control chart, using the agreed metrics and the correct finished-product state.
8. Archive the full traceability record and confirm when a new substrate, ink, press setting, or coating requires requalification.

The engineering conclusion

Color standards help production only when each one is used for its actual purpose. M0, M1, and M2 identify different measurement conditions. ISO 3664 addresses controlled viewing. FOGRA51, FOGRA52, and GRACoL2013/CRPC6 are distinct reference-data conditions. G7 and G7+ are calibration/alignment approaches. PSD governs digital process discipline. None should substitute for the others.

The most dangerous report is not necessarily one with a high ΔE. It may be a beautifully formatted report with a low ΔE measured against the wrong reference. Before deciding whether to change ink, rebuild a profile, or correct a press, establish what the target actually is and whether the measurement has the right to be compared with it. A disciplined reference chain turns color values from isolated numbers into defensible production evidence.

Sources and further reading

ISO 13655:2017. Graphic technology — Spectral measurement and colorimetric computation for graphic arts images. https://www.iso.org/standard/65430.html

ISO 3664:2025. Graphic technology and photography — Viewing conditions. https://www.iso.org/standard/83759.html

ISO 12647-2:2013. Process control — Offset lithographic processes. Current published edition, with a revision project underway. https://www.iso.org/standard/57833.html

Fogra. Characterization data. Includes FOGRA39, FOGRA51/PSO Coated v3, FOGRA52/PSO Uncoated v3, and other defined datasets. https://fogra.org/en/downloads/work-tools/characterisation-data

Fogra. ProcessStandard Digital (PSD). https://fogra.org/en/certification/digital-printing/psd

PRINTING United Alliance. GRACoL profiles, datasets and characterized reference printing conditions. https://www.printing.org/library/standards/specifications-for-print-production/gracol

ICC Profile Registry. GRACoL2013_CRPC6. https://registry.color.org/profile-registry/GRACoL2013_CRPC6

PRINTING United Alliance. G7 Master Facility Certification. https://www.printing.org/library/technical-excellence/certifications/g7-master-certification

PRINTING United Alliance. G7+ for Printers. https://www.printing.org/library/technical-excellence/certifications/g7plus-printers

Technical note: The production scenarios and descriptions of M-mode, OBA and gray-balance behavior are educational examples, not measured readings. Refer to the applicable licensed standards and official characterization files for contractual limits, reference patch values, and verification tolerances. This article does not assign universal ΔE pass limits to FOGRA, GRACoL, or G7 without a specified test protocol.