ISO 3664:2025

Graphic technology and photography - Viewing conditions

This document specifies viewing conditions for images on both reflective and transmissive media, such as prints (both photographic and photomechanical) and transparencies. This document applies to - critical evaluation of and comparison between transparencies, backlighted signs, reflection photographic or photomechanical prints and/or a reference object or image, - appraisal of the tone reproduction and colourfulness of prints and transparencies at illumination levels similar to those for practical use, including routine inspection, and - critical appraisal of transparencies which are viewed by projection, for comparison with prints, objects, or other reproductions. This document is not applicable to soft-proofing displays, for paper manufacture, and other applications outside of graphic technology and photography.

Technologie graphique et photographie — Conditions d'examen visuel

Grafična tehnologija in fotografija - Pogoji za vizualno opazovanje

Ta dokument določa pogoje za vizualno opazovanje slik na odsevnih in prepustnih medijih, kot so odtisi (fotografski in fotomehanski) ter prosojnice.  Ta dokument se uporablja za: – kritično oceno prosojnic, osvetljenih znakov in odsevnih fotografskih ali fotomehanskih odtisov ter za primerjavo med njimi in/ali referenčnim predmetom ali sliko; – oceno reprodukcije odtenkov in barvitosti odtisov ter prosojnic pri ravneh osvetlitve, podobnih tistim za praktično uporabo, vključno z rednim pregledom; ter – kritično oceno prosojnic, ki se opazujejo prek projekcije, za primerjavo z odtisi, predmeti ali drugimi reprodukcijami.  Ta dokument se ne uporablja za zaslone za simulacijo tiska, za proizvodnjo papirja in druge vrste uporabe, ki ne spadajo na področje grafične tehnologije in fotografije.

General Information

• Status: Published
• Publication Date: 10-Jul-2025
• ICS: 37.040.01 - Photography in general
• ICS: 37.100.01 - Graphic technology in general
• Technical Committee: ISO/TC 42 - Photography
• Drafting Committee: ISO/TC 42 - Photography
• Current Stage: 6060 - International Standard published
• Start Date: 11-Jul-2025
• Due Date: 21-Jun-2025
• Completion Date: 11-Jul-2025
• Ref Project: SIST ISO 3664:2025 - Graphic technology and photography - Viewing conditions

Relations

• Revises: ISO 3664:2009 - Graphic technology and photography - Viewing conditions
• Effective Date: 06-Jun-2022

Overview

ISO 3664:2025 - Graphic technology and photography - Viewing conditions - provides internationally agreed specifications for how images on reflective and transmissive media (photographic and photomechanical prints, transparencies, backlit signs) should be viewed for consistent, repeatable visual assessment and comparison. The fourth edition (2025) updates tolerances for modern lighting, adds D50 conditions with UV excluded (P3/P4), introduces a colour fidelity index for LED sources, and removes monitor/soft‑proofing conditions.

Key topics and technical requirements

• Scope: Applies to critical comparison, tone reproduction appraisal, routine inspection of prints and transparencies, and projected transparency comparison. Not applicable to soft‑proofing displays or paper manufacture.
• Reference illuminant: Uses CIE standard illuminant D50 as the basis for spectral requirements; new options exclude UV to reflect typical indoor LED lighting.
• Viewing condition classes:
  • P1 / P3 / T1 - conditions for critical comparison (prints and transparencies)
  • P2 / P4 - practical appraisal and routine inspection of prints
  • T2 - conditions for viewing small transparencies by projection
• Measured parameters:
  • Spectral power distribution and chromaticity of the illuminant
  • Illuminance (for reflection viewing) and luminance (for transmissive viewing)
  • Surround and backing, diffusion/uniformity, veiling flare, resolution and distortion for projection
• Conformance and test methods: Includes spectral measurements, illuminance/luminance testing, resolution assessment and a normative conformance test for UV content (Annex D).
• Maintenance and tolerances: Updated tolerances reflecting advances in LED technology and guidance for maintaining consistent viewing apparatus.
• Informative guidance: Annexes provide summaries of conditions, validity considerations, exhibition/judging guidelines, and best practices for multi‑site comparisons.

Applications and who uses it

ISO 3664:2025 is essential for professionals who require accurate visual evaluation and color matching, including:

• Photographers and photographic labs
• Print and prepress professionals, colour proofing houses
• Packaging and label manufacturers
• Sign and display producers (backlit/transmissive media)
• Museums, galleries, and curators evaluating prints and transparencies
• Quality control teams ensuring consistent tone and colour reproduction

Use cases include critical proof approvals, routine inspection of production prints, comparison between transparencies and prints, and setting up standardized viewing booths or lightboxes.

Related standards

• ISO 13655 (measurement conditions M1/M2) - referenced for correspondence between visual viewing conditions (P1/P2 vs P3/P4) and instrument measurement conditions.
• Developed by ISO/TC 42 (Photography) in collaboration with ISO/TC 130 (Graphic technology).

Keywords: ISO 3664:2025, viewing conditions, graphic technology, photography, D50, illuminance, luminance, LED lighting, UV excluded, color fidelity index, proofs, color matching.

Standards Content (Sample)

SLOVENSKI STANDARD
01-oktober-2025
Nadomešča:
SIST ISO 3664:2011
Grafična tehnologija in fotografija - Pogoji za vizualno opazovanje
Graphic technology and photography - Viewing conditions
Technologie graphique et photographie — Conditions d'examen visuel
Ta slovenski standard je istoveten z: ISO 3664:2025
ICS:
37.040.01 Fotografija na splošno Photography in general
37.100.01 Grafična tehnologija na Graphic technology in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

International
Standard
ISO 3664
Fourth edition
Graphic technology and
2025-07
photography — Viewing conditions
Technologie graphique et photographie — Conditions
d'examen visuel
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Viewing condition requirements. 5
4.1 General requirements .5
4.1.1 Applicability .5
4.1.2 Ambient conditions .5
4.1.3 Viewing apparatus .6
4.1.4 Spectral conditions for the reference illuminant .6
4.1.5 Maintenance .7
4.2 Conditions for critical comparison (ISO viewing conditions P1, P3, T1) .7
4.2.1 Applicability .7
4.2.2 Illumination .7
4.2.3 Illuminance (P1 and P3) .8
4.2.4 Surround and backing for reflection viewing (P1 and P3) .8
4.2.5 Luminance at the surface of the transparency illuminator (T1) .9
4.2.6 Transparency illuminator diffusion characteristics (T1) .9
4.2.7 Transparency surround (T1) .9
4.2.8 Relationship between transparency luminance and print illuminance (P1 or P3
and T1).9
4.3 Conditions for practical appraisal of prints (including routine inspection) (ISO viewing
condition P2 and P4) .10
4.3.1 Applicability .10
4.3.2 Illumination .10
4.3.3 Illuminance . . .10
4.3.4 Surround and backing .10
4.4 Conditions for viewing small transparencies by projection (ISO viewing conditions T2).11
4.4.1 Applicability .11
4.4.2 Illumination .11
4.4.3 Luminance .11
4.4.4 Uniformity of the projection screen luminance .11
4.4.5 Surround .11
4.4.6 Ambient light and veiling flare .11
4.4.7 Resolution .11
4.4.8 Distortion .11
5 Test methods .12
5.1 Spectral measurements . 12
5.2 Illuminance and luminance . 12
5.3 Resolution assessment for projection viewing apparatus . 12
Annex A (informative) Summary of viewing conditions specified in this document .13
Annex B (informative) Validity of requirements for reference viewing conditions for a print .15
Annex C (informative) Guidelines for judging and exhibiting photographs .18
Annex D (normative) Conformance test to UV content contained in illumination for P3 and P4
condition .20
Annex E (informative) Considerations for simultaneous comparison of samples between
multiple reference viewing environments .24
Bibliography .28

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography, in collaboration with
Technical Committee ISO/TC 130, Graphic technology.
This fourth edition cancels and replaces the third edition (ISO 3664:2009), which has been technically
revised.
The main changes are as follows:
— adding new viewing conditions P3/P4 for prints using CIE standard illuminant D50 with UV excluded;
— changing some tolerances according to the advance in lighting technology;
— introduced a colour fidelity index in response to the spread of LED lighting;
— removing the conditions for appraisal of images displayed on colour monitors.
This revision of ISO 3664:2009 meets the current needs of the Graphic Technology and Photographic
industries and minimizes differences between viewing equipment. It is noted that this revision contains
multiple specifications, each of which is appropriate to specific requirements. Users need to ensure that
they employ the specification which is appropriate to their application.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
While colour and density measurements play important roles in the control of colour reproduction, they
cannot replace the human observer for final assessment of the quality of complex images. Colour reflection
artwork, photographic transparencies, photographic prints, and photomechanical reproductions such as on-
press and off-press proofs, or press sheets, are commonly evaluated for their image and colour quality, or
compared critically with one another for fidelity of colour matching. Paper and other substrates contribute
to the colour appearance and controlling the colour of these is equally critical. However, it is noted that other
industries, such as the textile industry and the paper industry for unprinted paper, have their own set of
international standards which differ in illumination conditions from those recommended in this document.
There is no doubt that the best viewing condition for the visual assessment of colour is that in which the
product will be finally seen. Where this is known, and it is practical to do so, the various people in the
production chain can agree to use this viewing condition for all evaluation and comparison. However, it is
important that this is properly agreed upon in advance and that it is specified that such a viewing condition
is not ISO-defined.
Unfortunately, such agreement is often not practical. Even if a particular end-use condition is known, it can
be impractical to provide everybody in the production chain with sufficiently consistent viewing apparatus.
Differences in illumination and viewing conditions can cause corresponding differences in the colour
appearance of substrates, reproductions, and artwork. Such differences are likely to cause misunderstandings
about colour reproduction and processing. This document provides specifications for illumination and
viewing conditions that, when properly implemented, will reduce errors and misunderstandings caused by
such deficiencies and inconsistencies.
The illumination used to view colour photographic prints, photomechanical reproductions, and
transparencies needs to provide adequate amounts of radiant power from all parts of the spectrum to avoid
distorting their appearance from that observed under natural sources of illumination such as daylight. The
ultraviolet content is important where fluorescent samples, which are excited in this region, are encountered
and where the intended viewing environment includes UV; a phenomenon associated with many of the paper
substrates on which images are reproduced as well as with some of the dyes and pigments themselves.
To ensure consistency with previous editions of this document, as well as most of the equipment in current
use, reference spectral power distributions specified in this document are based on CIE standard illuminant
D50. Many of the reasons for the selection of CIE standard illuminant D50 in the first edition in 1974, as
opposed to any other CIE daylight illuminant, are equally applicable today. In this edition, the illumination
conditions of CIE standard illuminant D50 excluding the UV component are newly added as viewing
conditions P3 and P4 for prints. In practice, P3 and P4 can be achieved by turning off the energy below 420
nm to meet the P1 and P2 requirements.
Since the third edition was published, technological innovations have greatly improved the lighting quality
of LED lamps and lowered their cost. The Minamata Convention on Mercury came into effect in 2017, and
efforts to reduce the amount of mercury used have been promoted worldwide. Many manufacturers have
discontinued producing fluorescent lamps that use mercury and so the fluorescent lamps used for indoor
lighting have been rapidly replaced by LED lamps. Modern LED lamps have been commercially developed
which contain a short wavelength (440 nm to 470 nm) LED pump source and a broadband long wavelength
fluorescent emitter that together can produce a range of white lamp lights. Such sources contain very little
radiation that excites optical brightening agents used in most modern papers that serve as the substrates for
the printing of images for signs, packages, labels and publications. Therefore, in the case of print products
viewed in an indoor environment, optical brightening agents contained in the substrate don’t fluoresce
significantly. For print products that are expected to be used in such an environment, colour evaluations
with the M1 measurement condition of ISO 13655 and visual assessments under the P1/P2 reference
viewing conditions (CIE standard illuminant D50) of this document overestimate the effect of fluorescence
compared to that observed in the expected viewing environment. The P3/P4 reference viewing conditions
(CIE standard illuminant D50 excluding UV) are designed to evaluate print products that are expected to
be mainly viewed in an indoor environment. These viewing conditions correspond to the M2 measurement
condition of ISO 13655. Just as visual (colorimetric) assessments under P1/P2 conditions are consistent
with M1 measurements, visual assessments under P3/P4 conditions are consistent with M2 measurements.

v
Therefore, the viewing condition is selected to correspond with the measurement condition used to assess
the sample (P1/P2 for M1 and P3/P4 for M2).
Because it was very difficult to produce artificial sources of illumination which closely match the spectral
power distribution of natural daylight in the past, especially when fluorescent lamp technology was used
as the main light source for daylight simulators, it was important that the tolerances specified within this
document provided a compromise between that required for lamp manufacturing purposes and that for
consistent viewing. At present, fluorescent lamp technology is still used in the market, so the requirements
of previous edition are retained, but the criteria for higher precision matching that can be achieved with
new LED technology are added as recommendations. In this document three constraints which define the
characteristics of the light falling on the viewing plane apply, one directly and two indirectly, and all three
need to be met simultaneously if a viewing apparatus is to be considered as in conformance to this document.
Visual environments for colour inspections have been developed with arrays of LED emitters and fluorescent
coatings that will blend together to produce almost any desired spectral power distribution at the viewing
area of the inspection cabinet. The ability to set and control the luminous and spectral characteristics of
these clusters of LED emitters equals or in some cases exceeds the ability of the radiometric instruments
designed to characterize them. Where it is reasonable, the aims and tolerances have been adjusted to better
accommodate such solid-state lamp lights. The three requirements shown in the third edition are still
required in this fourth edition.
The chromaticity, which directly defines the colour of the illumination at the viewing surface, is specified
as that for CIE standard illuminant D50 and the tolerance by a circle in the CIE 1976 Uniform Chromaticity
Scale (UCS) diagram having a specified radius around that value.
It is important to establish spectral power distribution of the illumination conformance to that of CIE
standard illuminant D50 (including or excluding UV). As in the previous edition of this document, the
methods defined in CIE 13.3 to evaluate the colour rendering quality of a lamp and in ISO/CIE 23603 to
evaluate its ability to correctly predict metamers are used. These requirements continue to be important
to the graphic technology and photographic industries. In this edition, the method defined in CIE 224 which
evaluates the colour fidelity of a lamp has been added. The colour fidelity index was based on the fidelity
[9]
index of the Illuminating Engineering Society of North America and defined in TM-30-20. The colour
fidelity index has improved correlations with visual evaluations; however, it has not yet been widely used in
the market. It is expected that the colour fidelity index will become a requirement in a future revision, but
this edition includes it as a recommendation. The virtual metamers for CIE standard illuminant D50 from
ISO/CIE 23603 are used to assess the ultraviolet (UV) spectral fit and the visible (VIS) spectral fit separately.
The evaluation procedure for CIE standard illuminant D50 excluding UV is specified in Annex D. This test
verifies that the UV content of the light source corresponds to the M2 measurement condition. Tolerances
for the evaluation indices described above were validated using commercially available LED lamps and the
results are shown in Annex B.
The perceived tonal scale and colours of a print or transparency can be significantly influenced by the
chromaticity and luminance of other objects and surfaces in the field of view. For this reason, immediate
surround and ambient conditions, which will possibly affect the state of visual adaptation, need to be
designed to avoid any significant effects on the perception of colour and tone. Such specifications are
provided in this document.
This document is premised on a single viewing condition. In the case of multiple reference viewing conditions,
chromatic adaptation of an observer to multiple light sources can be insufficient, so a stricter match of the
chromaticity of the light sources between the viewing conditions will be necessary. Considerations for
simultaneous comparison of samples between multiple reference viewing environments are provided in
Annex E.
Experience in the industries covered by this document has revealed the need for two levels of illumination;
a high level for critical evaluation and comparison, and a lower level for appraising the tone scale of an
individual image under illumination levels similar to the levels under which it will be finally viewed. This
document specifies these two levels of illumination.
The higher illumination level is essential to graphic technology where a comparison is being made, such as
between original artwork and proof, or to evaluate small colour differences between proof and press sheet,
to control a printing operation. It is effective in these situations because it enhances the visibility of any

vi
differences. The high level of illumination is also appropriate in photography when comparing transparencies
or when critically evaluating a single image to assess the darkest tones that can be reproduced.
Since, despite adaptation, the level of illumination has quite a significant effect on the appearance of an
image, the lower level is required to appraise the image at a level similar to that in which it will be finally
viewed. Although, it is recognized that quite a wide range of illumination levels can be encountered in
practical viewing situations, the lower level was chosen to be representative of the range encountered. For
this reason, it is applicable to aesthetic appraisal, including the conditions for routine inspection of prints.
As a special use-case, a viewing condition for judging and exhibiting photographs is considered and some
guidelines are provided in Annex C.
The viewing of transparencies is specified for direct viewing. Additional conditions are also specified for
cases where transparencies are viewed by projection and where transparencies are to be compared to a
print. The surround specified for transparency viewing recognizes the way that a transparency needs to
be viewed for optimum visibility of the dark tones but acknowledges that practical viewing equipment is
likely to have ambient conditions that introduce some viewing flare. This problem is made worse by the light
grey walls of the viewing cabinet, that are intended to redirect the diffuse lamp light from incandescent and
fluorescent lamps back down onto the bottom of the cabinet. The combination of surround and flare produce
an appearance that is not always representative of how the transparency would look in a typically lighted
room. Solid-state, LED, lamps tend to produce more directional light fluxes and thus, it is possible to produce
the required illumination levels without the need for the diffusely reflecting walls. This reduces the viewing
flare and provides a more useful viewing environment for higher contrast images such as transparencies.
Small transparencies are commonly evaluated in graphic technology by direct viewing. When it is necessary
to view transparencies directly, they need to be viewed according to the conditions specified for that
situation. However, for some purposes, smaller transparencies are not viewed directly because the viewing
distance for correct perspective and perception of detail is too small for visual comfort. Furthermore,
when small transparencies are reproduced for publication or other purposes, they are usually enlarged.
To ease comparison, it is helpful to enlarge the transparency image when comparing it to the print. For
these reasons, a viewing condition can be required which provides a magnified image when viewed at an
appropriate distance.
Colour image displays are increasingly being used to view digital images in graphic technology and
photography. The setup and control of digital colour displays are now standardized in ISO and IEC documents
from technical committees, including ISO/TC 130 and ISO/TC 159, and IEC/TC 110.
The specifications for images viewed on colour monitors are no longer provided in this document, as this
process is beyond the scope of this document and reference documents are provided in the Bibliography.

vii
International Standard ISO 3664:2025(en)
Graphic technology and photography — Viewing conditions
1 Scope
This document specifies viewing conditions for images on both reflective and transmissive media, such as
prints (both photographic and photomechanical) and transparencies.
This document applies to
— critical evaluation of and comparison between transparencies, backlighted signs, reflection photographic
or photomechanical prints and/or a reference object or image,
— appraisal of the tone reproduction and colourfulness of prints and transparencies at illumination levels
similar to those for practical use, including routine inspection, and
— critical appraisal of transparencies which are viewed by projection, for comparison with prints, objects,
or other reproductions.
This document is not applicable to soft-proofing displays, for paper manufacture, and other applications
outside of graphic technology and photography.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 5-2, Photography and graphic technology — Density measurements — Part 2: Geometric conditions for
transmittance density
ISO 5-3, Photography and graphic technology — Density measurements — Part 3: Spectral conditions
ISO 13655:2017, Graphic technology — Spectral measurement and colorimetric computation for graphic arts images
ISO/CIE 23603, Standard method of assessing the spectral quality of daylight simulators for visual appraisal and
measurement of colour
CIE 13.3, Method of measuring and specifying colour rendering properties of light sources
CIE 15, Colorimetry, 4th Edition
CIE 224, Colour Fidelity Index for accurate scientific use
ISO/CIE 19476, Characterization of the performance of illuminance meters and luminance meters
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

3.1
ambient condition
visual environment outside a surround
Note 1 to entry: Ambient light can affect an appraisal of prints in the following ways: illumination contamination,
increasing viewing flare, and visual adaptation of observer just before evaluation.
3.2
backing
material placed behind and in contact with the specimen during viewing
[SOURCE: ISO 13655:2017, 3.12, modified — “specimen” deleted in the term. “viewing” replaced “measuring”.
Note 1 to entry deleted.]
3.3
chromaticity
property of a colour stimulus defined by its chromaticity coordinates, or by its dominant or complementary
wavelength and purity taken together
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-23-052]
3.4
colour rendering index
CRI
measure of the degree to which the psychophysical colour of an object illuminated by a test illuminant
conforms to that of the same object illuminated by the reference illuminant, suitable allowance having been
made for the state of chromatic adaptation
Note 1 to entry: The evaluation method for CIE Colour Rendering Index is specified in CIE 13.3.
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-22-109]
3.5
colour fidelity index
measure of the degree to which the colour appearance of objects illuminated by a test illuminant matches
that of the same objects illuminated by the reference illuminant
Note 1 to entry: The evaluation method for CIE 2017 Colour Fidelity Index is specified in CIE 224.
3.6
correlated colour temperature
temperature of a Planckian radiator having the chromaticity (3.3) nearest the chromaticity (3.3) associated
′′
with the given spectral distribution on a modified 1976 UCS diagram where uv, are the coordinates of
the Plancking locus and the test stimulus
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition 17-203-068]
3.7
illuminance
density of incident luminous flux with respect to area at a point on a real or imaginary surface
dΦ
v
E =
v
dA
where Φ is luminous flux and A is the area at a point on which the luminous flux is incident
v
-2
Note 1 to entry: The illuminance is expressed in lux (lx = lm ⋅ m ).
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-21-060]

3.8
illuminant
radiation with a relative spectral power distribution defined over the wavelength range that influences
object-colour perception
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-23-018]
3.9
luminance
density of luminous intensity with respect to project area in a specified direction at a specified point on a
real or imaginary surface
∂ Φ
V
L =
V
∂⋅A cos()θ ⋅∂Ω
where
∂ Φ is the luminous flux transmitted by an elementary beam passing through the given point and
v
propagating in the solid angle ∂Ω containing the given direction;
∂A is the area of a section of that beam containing the given point;
θ is the angle between the normal to that section and the direction of the beam
-2 -2 -1
Note 1 to entry: The luminance is expressed in candela per square metre (cd ⋅ m = lm ⋅ m ⋅sr )
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-21-050]
3.10
luminous reflectance
ratio of the luminous flux reflected from a surface to the luminous flux incident on the surface
3.11
off-press proof
print produced by a method other than press printing whose purpose is to show the results of the colour
separation process in a way that closely simulates the results on a production press
3.12
on-press proof
print produced by press printing (production or proof press) whose purpose is to show the results of the
colour separation process in a way that closely simulates the results on a production press
3.13
original
the scene or hardcopy from which image information is obtained, using an image capture device, in a
reproduction process
Note 1 to entry: As used in graphic technology, the original is typically a print or transparency, and the capture device is
usually an input scanner or, occasionally, a process camera. In photography the term original scene is sometimes used.
3.14
print
two-dimensional hardcopy form of an image intended for viewing
Note 1 to entry: In still photography and graphic technology, the term print is reserved for reflection hardcopy; a
medium designed to be viewed by reflected light.
3.15
relative spectral power distribution
ratio of the spectral power distribution of a source or illuminant (3.9) to a fixed reference value which can be
an average value, a maximum value, or an arbitrarily chosen value of this distribution

3.16
source
primary emitter of electromagnetic radiation
3.17
surround
area adjacent to the border of an image which, upon viewing the image, can affect the local state of adaptation
of the eye
Note 1 to entry: The surround, which can have a significant effect on the perceived tone and colour reproduction of
an image, is not to be confused with any border immediately surrounding the image, such as any unprinted white
substrate for reflection copy or the unexposed border present on many transparencies.
Note 2 to entry: The surround is in the plane of viewing and is an area that is seen when observing the test sample. The
side walls of a viewing cabinet and backing material are not included in the surround.
3.18
transparency
two-dimensional hardcopy form of an image designed to be viewed by transmitted light
3.19
transparency illuminator
apparatus used for back illumination of a transparency (3.18)
3.20
veiling flare
relatively uniform but unwanted irradiation in the image plane of an optical system, caused by the scattering
and reflection of a proportion of the radiation which enters the system through its normal entrance aperture
where the radiation can be from inside or outside the field of view of the system
Note 1 to entry: Light leaks in an optical system housing can cause additional unwanted irradiation of the image plane.
This irradiation can resemble veiling flare.
3.21
veiling glare
light, reflected from an imaging medium, that has not been modulated by the means used to produce the image
Note 1 to entry: Veiling glare lightens the darker parts and reduces the contrast of an image.
3.22
viewing flare
veiling glare that is observed in a viewing environment but not accounted for in measurements made using a
prescribed measurement geometry
Note 1 to entry: The viewing flare is expressed as a percentage of the luminance of the adapted white.
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-32-067]
3.23
virtual metamer
set of spectral radiance factors, not based on physical samples, which provide metameric matches for
specific standard daylight illuminants
Note 1 to entry: Virtual metamers are used to test and classify illumination sources which simulate daylight according
to the method provided in ISO/CIE 23603. This classification is accomplished by calculating the average of the colour
differences obtained for these metamers between the illumination source in question and a CIE standard illuminant.
Although it can be possible to construct physical realizations of some virtual metamers, the fact that they are not
required to be real allows greater flexibility in their design.

4 Viewing condition requirements
4.1 General requirements
4.1.1 Applicability
The requirements of this subclause (4.1) are general and apply to all viewing applications. Subclauses 4.2
through 4.4 contain additional requirements specific to a variety of viewing applications.
The specific viewing applications are
— conditions for critical comparison (P1, P3 and T1),
— conditions for practical appraisal of prints (P2 and P4), and
— conditions for viewing small transparencies by projection (T2)
NOTE 1 For ease of reference, each viewing condition described in this document has been given an alphanumeric
designation. This can be useful in describing or specifying conditions: e.g. "ISO 3664 viewing condition P2".
NOTE 2 The details of P1, P2, P3, P4, T1 and T2 are provided in 4.2.1, 4.3.1 and 4.4.1.
Print workflows are out of scope of this document however the following should be noted when selecting
measurement conditions M1 or M2 (ISO 13655) and corresponding viewing conditions. For print viewing,
if the amount of optical brightening agent in a substrate is small and its effect is negligible, M1 and M2
measurements will match, and print appearance will be the same under P1 and P3 or under P2 and P4
viewing conditions. Measurement of prints using M1 is consistent with P1 and P2 viewing conditions, and
measurement of prints using M2 is consistent with P3 and P4 viewing conditions. When prints with optical
brightening agents are viewed in environments with very little or no UV radiation, such as LED lamps that
typically emit very little UV, the P3 or P4 reference viewing conditions are most appropriate. When prints
with optical brightening agents are viewed in an environment that includes UV radiation of similar level to
that of D50, such as with natural daylight or D50 simulators that include UV, the P1 or P2 viewing conditions
are most appropriate.
NOTE 3 This guidance minimises differences between the reference viewing environment and intended viewing
environment for prints that fluoresce in the presence of UV. Where the intended viewing environment has a correlated
colour temperature that is substantially different from that of D50, there can be additional significant perceived
colour differences compared with all four reference viewing environments. These differences are further increased
where the lamps used in the intended viewing environment have poor colour fidelity or a CCT below 3 000 K.
4.1.2 Ambient conditions
The visual environment shall be designed to minimize interference with the viewing task. It is important to
eliminate extraneous conditions that affect the appraisal of prints or transparencies, and an observer should
avoid making judgements immediately after entering a new illumination environment because it takes a few
minutes to visually adapt fully to that new environment.
Extraneous light, whether from sources or reflected by objects and surfaces, should be baffled from view
and from illuminating the print, transparency, or other image being evaluated.
A viewing cabinet may be used to minimize the impact of any environmental illumination.
No strongly coloured surfaces (including clothing) should be visible in the viewing environment. In keeping
with the need to avoid visual distractions in the viewing field, equipment, controls and other objects should
be approximately neutral in colour. Displays used for press control should produce only grey-scale images
and their luminance should be limited to avoid distractions.
NOTE The presence of bright or strongly coloured objects within the viewing environment is a potential problem
because they can cause reflections affecting the colour appearance of the objects being assessed.

4.1.3 Viewing apparatus
To conform to this document, the values specified shall be achieved at the surface of viewing. The specified
relative spectral power distribution applies to the illuminated surface rather than to the source (or lamp)
because the light from the source may be modified by reflecting and transmitting components of the
apparatus, and the required relative spectral power distribution may be obtained from a mixture of light
from different sources.
The source, image being viewed, and observer's eyes shall be positioned to minimize the amount of light that
is reflected specularly toward the eyes of an observer on or near the normal to the centre of the viewing
surface.
When a viewing cabinet is used, the walls of the viewing cabinets shall be matte and neutral (C* ≤ 2,0 is
ab
required, and C* ≤ 1,5 is recommended) and the metric lightness (L*) shall be 80 or less and should be
ab
between 50 and 70. When making critical judgements on the details of a print, the light from the walls
can become a source of veiling flare. In those cases, a mid-grey of 20 % luminous reflectance (L* ≈ 50) is
recommended. The walls may be made even darker, but no lower than 16 of L*, if the suppression of gloss or
specular highlight are a concern. The use of dark walls less than 50 shall be noted in the report.
Since a table or a bottom of the viewing cabinet on which the sample is placed can become a surround, it
should conform to the surround specification in 4.2.4 for reflection viewing or 4.2.7 for transparency.
A viewing cabinet claiming compliance with this document shall clearly indicate the set of viewing conditions
(P1, P2, P3, P4) it meets and shall be accompanied by a report containing the results of the assessment of
the requirements listed in Table A.1 and A.2 as appropriate. A viewing cabinet providing multiple viewing
conditions shall explain how each viewing condition is achieved and should indicate the viewing condition
to which it is currently set.
4.1.4 Spectral conditions for the reference illuminant
The relative spectral power distribution of the reference illuminant for both prints and transparencies shall
1)
be based on CIE standard illuminant D50 as defined in CIE 15:2018 (see Table 5 of CIE 15:2018 ) including
or excluding UV. This represents a phase of natural daylight having a correlated colour temperature of
approximately 5 000 K. The chromaticity coordinates of CIE standard illuminant D50 are x = 0,347 7 and
y = 0,359
...

International
Standard
ISO 3664
Fourth edition
Graphic technology and
2025-07
photography — Viewing conditions
Technologie graphique et photographie — Conditions
d'examen visuel
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Viewing condition requirements. 5
4.1 General requirements .5
4.1.1 Applicability .5
4.1.2 Ambient conditions .5
4.1.3 Viewing apparatus .6
4.1.4 Spectral conditions for the reference illuminant .6
4.1.5 Maintenance .7
4.2 Conditions for critical comparison (ISO viewing conditions P1, P3, T1) .7
4.2.1 Applicability .7
4.2.2 Illumination .7
4.2.3 Illuminance (P1 and P3) .8
4.2.4 Surround and backing for reflection viewing (P1 and P3) .8
4.2.5 Luminance at the surface of the transparency illuminator (T1) .9
4.2.6 Transparency illuminator diffusion characteristics (T1) .9
4.2.7 Transparency surround (T1) .9
4.2.8 Relationship between transparency luminance and print illuminance (P1 or P3
and T1).9
4.3 Conditions for practical appraisal of prints (including routine inspection) (ISO viewing
condition P2 and P4) .10
4.3.1 Applicability .10
4.3.2 Illumination .10
4.3.3 Illuminance . . .10
4.3.4 Surround and backing .10
4.4 Conditions for viewing small transparencies by projection (ISO viewing conditions T2).11
4.4.1 Applicability .11
4.4.2 Illumination .11
4.4.3 Luminance .11
4.4.4 Uniformity of the projection screen luminance .11
4.4.5 Surround .11
4.4.6 Ambient light and veiling flare .11
4.4.7 Resolution .11
4.4.8 Distortion .11
5 Test methods .12
5.1 Spectral measurements . 12
5.2 Illuminance and luminance . 12
5.3 Resolution assessment for projection viewing apparatus . 12
Annex A (informative) Summary of viewing conditions specified in this document .13
Annex B (informative) Validity of requirements for reference viewing conditions for a print .15
Annex C (informative) Guidelines for judging and exhibiting photographs .18
Annex D (normative) Conformance test to UV content contained in illumination for P3 and P4
condition .20
Annex E (informative) Considerations for simultaneous comparison of samples between
multiple reference viewing environments .24
Bibliography .28

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 42, Photography, in collaboration with
Technical Committee ISO/TC 130, Graphic technology.
This fourth edition cancels and replaces the third edition (ISO 3664:2009), which has been technically
revised.
The main changes are as follows:
— adding new viewing conditions P3/P4 for prints using CIE standard illuminant D50 with UV excluded;
— changing some tolerances according to the advance in lighting technology;
— introduced a colour fidelity index in response to the spread of LED lighting;
— removing the conditions for appraisal of images displayed on colour monitors.
This revision of ISO 3664:2009 meets the current needs of the Graphic Technology and Photographic
industries and minimizes differences between viewing equipment. It is noted that this revision contains
multiple specifications, each of which is appropriate to specific requirements. Users need to ensure that
they employ the specification which is appropriate to their application.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
While colour and density measurements play important roles in the control of colour reproduction, they
cannot replace the human observer for final assessment of the quality of complex images. Colour reflection
artwork, photographic transparencies, photographic prints, and photomechanical reproductions such as on-
press and off-press proofs, or press sheets, are commonly evaluated for their image and colour quality, or
compared critically with one another for fidelity of colour matching. Paper and other substrates contribute
to the colour appearance and controlling the colour of these is equally critical. However, it is noted that other
industries, such as the textile industry and the paper industry for unprinted paper, have their own set of
international standards which differ in illumination conditions from those recommended in this document.
There is no doubt that the best viewing condition for the visual assessment of colour is that in which the
product will be finally seen. Where this is known, and it is practical to do so, the various people in the
production chain can agree to use this viewing condition for all evaluation and comparison. However, it is
important that this is properly agreed upon in advance and that it is specified that such a viewing condition
is not ISO-defined.
Unfortunately, such agreement is often not practical. Even if a particular end-use condition is known, it can
be impractical to provide everybody in the production chain with sufficiently consistent viewing apparatus.
Differences in illumination and viewing conditions can cause corresponding differences in the colour
appearance of substrates, reproductions, and artwork. Such differences are likely to cause misunderstandings
about colour reproduction and processing. This document provides specifications for illumination and
viewing conditions that, when properly implemented, will reduce errors and misunderstandings caused by
such deficiencies and inconsistencies.
The illumination used to view colour photographic prints, photomechanical reproductions, and
transparencies needs to provide adequate amounts of radiant power from all parts of the spectrum to avoid
distorting their appearance from that observed under natural sources of illumination such as daylight. The
ultraviolet content is important where fluorescent samples, which are excited in this region, are encountered
and where the intended viewing environment includes UV; a phenomenon associated with many of the paper
substrates on which images are reproduced as well as with some of the dyes and pigments themselves.
To ensure consistency with previous editions of this document, as well as most of the equipment in current
use, reference spectral power distributions specified in this document are based on CIE standard illuminant
D50. Many of the reasons for the selection of CIE standard illuminant D50 in the first edition in 1974, as
opposed to any other CIE daylight illuminant, are equally applicable today. In this edition, the illumination
conditions of CIE standard illuminant D50 excluding the UV component are newly added as viewing
conditions P3 and P4 for prints. In practice, P3 and P4 can be achieved by turning off the energy below 420
nm to meet the P1 and P2 requirements.
Since the third edition was published, technological innovations have greatly improved the lighting quality
of LED lamps and lowered their cost. The Minamata Convention on Mercury came into effect in 2017, and
efforts to reduce the amount of mercury used have been promoted worldwide. Many manufacturers have
discontinued producing fluorescent lamps that use mercury and so the fluorescent lamps used for indoor
lighting have been rapidly replaced by LED lamps. Modern LED lamps have been commercially developed
which contain a short wavelength (440 nm to 470 nm) LED pump source and a broadband long wavelength
fluorescent emitter that together can produce a range of white lamp lights. Such sources contain very little
radiation that excites optical brightening agents used in most modern papers that serve as the substrates for
the printing of images for signs, packages, labels and publications. Therefore, in the case of print products
viewed in an indoor environment, optical brightening agents contained in the substrate don’t fluoresce
significantly. For print products that are expected to be used in such an environment, colour evaluations
with the M1 measurement condition of ISO 13655 and visual assessments under the P1/P2 reference
viewing conditions (CIE standard illuminant D50) of this document overestimate the effect of fluorescence
compared to that observed in the expected viewing environment. The P3/P4 reference viewing conditions
(CIE standard illuminant D50 excluding UV) are designed to evaluate print products that are expected to
be mainly viewed in an indoor environment. These viewing conditions correspond to the M2 measurement
condition of ISO 13655. Just as visual (colorimetric) assessments under P1/P2 conditions are consistent
with M1 measurements, visual assessments under P3/P4 conditions are consistent with M2 measurements.

v
Therefore, the viewing condition is selected to correspond with the measurement condition used to assess
the sample (P1/P2 for M1 and P3/P4 for M2).
Because it was very difficult to produce artificial sources of illumination which closely match the spectral
power distribution of natural daylight in the past, especially when fluorescent lamp technology was used
as the main light source for daylight simulators, it was important that the tolerances specified within this
document provided a compromise between that required for lamp manufacturing purposes and that for
consistent viewing. At present, fluorescent lamp technology is still used in the market, so the requirements
of previous edition are retained, but the criteria for higher precision matching that can be achieved with
new LED technology are added as recommendations. In this document three constraints which define the
characteristics of the light falling on the viewing plane apply, one directly and two indirectly, and all three
need to be met simultaneously if a viewing apparatus is to be considered as in conformance to this document.
Visual environments for colour inspections have been developed with arrays of LED emitters and fluorescent
coatings that will blend together to produce almost any desired spectral power distribution at the viewing
area of the inspection cabinet. The ability to set and control the luminous and spectral characteristics of
these clusters of LED emitters equals or in some cases exceeds the ability of the radiometric instruments
designed to characterize them. Where it is reasonable, the aims and tolerances have been adjusted to better
accommodate such solid-state lamp lights. The three requirements shown in the third edition are still
required in this fourth edition.
The chromaticity, which directly defines the colour of the illumination at the viewing surface, is specified
as that for CIE standard illuminant D50 and the tolerance by a circle in the CIE 1976 Uniform Chromaticity
Scale (UCS) diagram having a specified radius around that value.
It is important to establish spectral power distribution of the illumination conformance to that of CIE
standard illuminant D50 (including or excluding UV). As in the previous edition of this document, the
methods defined in CIE 13.3 to evaluate the colour rendering quality of a lamp and in ISO/CIE 23603 to
evaluate its ability to correctly predict metamers are used. These requirements continue to be important
to the graphic technology and photographic industries. In this edition, the method defined in CIE 224 which
evaluates the colour fidelity of a lamp has been added. The colour fidelity index was based on the fidelity
[9]
index of the Illuminating Engineering Society of North America and defined in TM-30-20. The colour
fidelity index has improved correlations with visual evaluations; however, it has not yet been widely used in
the market. It is expected that the colour fidelity index will become a requirement in a future revision, but
this edition includes it as a recommendation. The virtual metamers for CIE standard illuminant D50 from
ISO/CIE 23603 are used to assess the ultraviolet (UV) spectral fit and the visible (VIS) spectral fit separately.
The evaluation procedure for CIE standard illuminant D50 excluding UV is specified in Annex D. This test
verifies that the UV content of the light source corresponds to the M2 measurement condition. Tolerances
for the evaluation indices described above were validated using commercially available LED lamps and the
results are shown in Annex B.
The perceived tonal scale and colours of a print or transparency can be significantly influenced by the
chromaticity and luminance of other objects and surfaces in the field of view. For this reason, immediate
surround and ambient conditions, which will possibly affect the state of visual adaptation, need to be
designed to avoid any significant effects on the perception of colour and tone. Such specifications are
provided in this document.
This document is premised on a single viewing condition. In the case of multiple reference viewing conditions,
chromatic adaptation of an observer to multiple light sources can be insufficient, so a stricter match of the
chromaticity of the light sources between the viewing conditions will be necessary. Considerations for
simultaneous comparison of samples between multiple reference viewing environments are provided in
Annex E.
Experience in the industries covered by this document has revealed the need for two levels of illumination;
a high level for critical evaluation and comparison, and a lower level for appraising the tone scale of an
individual image under illumination levels similar to the levels under which it will be finally viewed. This
document specifies these two levels of illumination.
The higher illumination level is essential to graphic technology where a comparison is being made, such as
between original artwork and proof, or to evaluate small colour differences between proof and press sheet,
to control a printing operation. It is effective in these situations because it enhances the visibility of any

vi
differences. The high level of illumination is also appropriate in photography when comparing transparencies
or when critically evaluating a single image to assess the darkest tones that can be reproduced.
Since, despite adaptation, the level of illumination has quite a significant effect on the appearance of an
image, the lower level is required to appraise the image at a level similar to that in which it will be finally
viewed. Although, it is recognized that quite a wide range of illumination levels can be encountered in
practical viewing situations, the lower level was chosen to be representative of the range encountered. For
this reason, it is applicable to aesthetic appraisal, including the conditions for routine inspection of prints.
As a special use-case, a viewing condition for judging and exhibiting photographs is considered and some
guidelines are provided in Annex C.
The viewing of transparencies is specified for direct viewing. Additional conditions are also specified for
cases where transparencies are viewed by projection and where transparencies are to be compared to a
print. The surround specified for transparency viewing recognizes the way that a transparency needs to
be viewed for optimum visibility of the dark tones but acknowledges that practical viewing equipment is
likely to have ambient conditions that introduce some viewing flare. This problem is made worse by the light
grey walls of the viewing cabinet, that are intended to redirect the diffuse lamp light from incandescent and
fluorescent lamps back down onto the bottom of the cabinet. The combination of surround and flare produce
an appearance that is not always representative of how the transparency would look in a typically lighted
room. Solid-state, LED, lamps tend to produce more directional light fluxes and thus, it is possible to produce
the required illumination levels without the need for the diffusely reflecting walls. This reduces the viewing
flare and provides a more useful viewing environment for higher contrast images such as transparencies.
Small transparencies are commonly evaluated in graphic technology by direct viewing. When it is necessary
to view transparencies directly, they need to be viewed according to the conditions specified for that
situation. However, for some purposes, smaller transparencies are not viewed directly because the viewing
distance for correct perspective and perception of detail is too small for visual comfort. Furthermore,
when small transparencies are reproduced for publication or other purposes, they are usually enlarged.
To ease comparison, it is helpful to enlarge the transparency image when comparing it to the print. For
these reasons, a viewing condition can be required which provides a magnified image when viewed at an
appropriate distance.
Colour image displays are increasingly being used to view digital images in graphic technology and
photography. The setup and control of digital colour displays are now standardized in ISO and IEC documents
from technical committees, including ISO/TC 130 and ISO/TC 159, and IEC/TC 110.
The specifications for images viewed on colour monitors are no longer provided in this document, as this
process is beyond the scope of this document and reference documents are provided in the Bibliography.

vii
International Standard ISO 3664:2025(en)
Graphic technology and photography — Viewing conditions
1 Scope
This document specifies viewing conditions for images on both reflective and transmissive media, such as
prints (both photographic and photomechanical) and transparencies.
This document applies to
— critical evaluation of and comparison between transparencies, backlighted signs, reflection photographic
or photomechanical prints and/or a reference object or image,
— appraisal of the tone reproduction and colourfulness of prints and transparencies at illumination levels
similar to those for practical use, including routine inspection, and
— critical appraisal of transparencies which are viewed by projection, for comparison with prints, objects,
or other reproductions.
This document is not applicable to soft-proofing displays, for paper manufacture, and other applications
outside of graphic technology and photography.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 5-2, Photography and graphic technology — Density measurements — Part 2: Geometric conditions for
transmittance density
ISO 5-3, Photography and graphic technology — Density measurements — Part 3: Spectral conditions
ISO 13655:2017, Graphic technology — Spectral measurement and colorimetric computation for graphic arts images
ISO/CIE 23603, Standard method of assessing the spectral quality of daylight simulators for visual appraisal and
measurement of colour
CIE 13.3, Method of measuring and specifying colour rendering properties of light sources
CIE 15, Colorimetry, 4th Edition
CIE 224, Colour Fidelity Index for accurate scientific use
ISO/CIE 19476, Characterization of the performance of illuminance meters and luminance meters
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

3.1
ambient condition
visual environment outside a surround
Note 1 to entry: Ambient light can affect an appraisal of prints in the following ways: illumination contamination,
increasing viewing flare, and visual adaptation of observer just before evaluation.
3.2
backing
material placed behind and in contact with the specimen during viewing
[SOURCE: ISO 13655:2017, 3.12, modified — “specimen” deleted in the term. “viewing” replaced “measuring”.
Note 1 to entry deleted.]
3.3
chromaticity
property of a colour stimulus defined by its chromaticity coordinates, or by its dominant or complementary
wavelength and purity taken together
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-23-052]
3.4
colour rendering index
CRI
measure of the degree to which the psychophysical colour of an object illuminated by a test illuminant
conforms to that of the same object illuminated by the reference illuminant, suitable allowance having been
made for the state of chromatic adaptation
Note 1 to entry: The evaluation method for CIE Colour Rendering Index is specified in CIE 13.3.
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-22-109]
3.5
colour fidelity index
measure of the degree to which the colour appearance of objects illuminated by a test illuminant matches
that of the same objects illuminated by the reference illuminant
Note 1 to entry: The evaluation method for CIE 2017 Colour Fidelity Index is specified in CIE 224.
3.6
correlated colour temperature
temperature of a Planckian radiator having the chromaticity (3.3) nearest the chromaticity (3.3) associated
′′
with the given spectral distribution on a modified 1976 UCS diagram where uv, are the coordinates of
the Plancking locus and the test stimulus
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition 17-203-068]
3.7
illuminance
density of incident luminous flux with respect to area at a point on a real or imaginary surface
dΦ
v
E =
v
dA
where Φ is luminous flux and A is the area at a point on which the luminous flux is incident
v
-2
Note 1 to entry: The illuminance is expressed in lux (lx = lm ⋅ m ).
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-21-060]

3.8
illuminant
radiation with a relative spectral power distribution defined over the wavelength range that influences
object-colour perception
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-23-018]
3.9
luminance
density of luminous intensity with respect to project area in a specified direction at a specified point on a
real or imaginary surface
∂ Φ
V
L =
V
∂⋅A cos()θ ⋅∂Ω
where
∂ Φ is the luminous flux transmitted by an elementary beam passing through the given point and
v
propagating in the solid angle ∂Ω containing the given direction;
∂A is the area of a section of that beam containing the given point;
θ is the angle between the normal to that section and the direction of the beam
-2 -2 -1
Note 1 to entry: The luminance is expressed in candela per square metre (cd ⋅ m = lm ⋅ m ⋅sr )
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-21-050]
3.10
luminous reflectance
ratio of the luminous flux reflected from a surface to the luminous flux incident on the surface
3.11
off-press proof
print produced by a method other than press printing whose purpose is to show the results of the colour
separation process in a way that closely simulates the results on a production press
3.12
on-press proof
print produced by press printing (production or proof press) whose purpose is to show the results of the
colour separation process in a way that closely simulates the results on a production press
3.13
original
the scene or hardcopy from which image information is obtained, using an image capture device, in a
reproduction process
Note 1 to entry: As used in graphic technology, the original is typically a print or transparency, and the capture device is
usually an input scanner or, occasionally, a process camera. In photography the term original scene is sometimes used.
3.14
print
two-dimensional hardcopy form of an image intended for viewing
Note 1 to entry: In still photography and graphic technology, the term print is reserved for reflection hardcopy; a
medium designed to be viewed by reflected light.
3.15
relative spectral power distribution
ratio of the spectral power distribution of a source or illuminant (3.9) to a fixed reference value which can be
an average value, a maximum value, or an arbitrarily chosen value of this distribution

3.16
source
primary emitter of electromagnetic radiation
3.17
surround
area adjacent to the border of an image which, upon viewing the image, can affect the local state of adaptation
of the eye
Note 1 to entry: The surround, which can have a significant effect on the perceived tone and colour reproduction of
an image, is not to be confused with any border immediately surrounding the image, such as any unprinted white
substrate for reflection copy or the unexposed border present on many transparencies.
Note 2 to entry: The surround is in the plane of viewing and is an area that is seen when observing the test sample. The
side walls of a viewing cabinet and backing material are not included in the surround.
3.18
transparency
two-dimensional hardcopy form of an image designed to be viewed by transmitted light
3.19
transparency illuminator
apparatus used for back illumination of a transparency (3.18)
3.20
veiling flare
relatively uniform but unwanted irradiation in the image plane of an optical system, caused by the scattering
and reflection of a proportion of the radiation which enters the system through its normal entrance aperture
where the radiation can be from inside or outside the field of view of the system
Note 1 to entry: Light leaks in an optical system housing can cause additional unwanted irradiation of the image plane.
This irradiation can resemble veiling flare.
3.21
veiling glare
light, reflected from an imaging medium, that has not been modulated by the means used to produce the image
Note 1 to entry: Veiling glare lightens the darker parts and reduces the contrast of an image.
3.22
viewing flare
veiling glare that is observed in a viewing environment but not accounted for in measurements made using a
prescribed measurement geometry
Note 1 to entry: The viewing flare is expressed as a percentage of the luminance of the adapted white.
nd
[SOURCE: CIE S 17:2020 International Lighting Vocabulary, 2 edition, 17-32-067]
3.23
virtual metamer
set of spectral radiance factors, not based on physical samples, which provide metameric matches for
specific standard daylight illuminants
Note 1 to entry: Virtual metamers are used to test and classify illumination sources which simulate daylight according
to the method provided in ISO/CIE 23603. This classification is accomplished by calculating the average of the colour
differences obtained for these metamers between the illumination source in question and a CIE standard illuminant.
Although it can be possible to construct physical realizations of some virtual metamers, the fact that they are not
required to be real allows greater flexibility in their design.

4 Viewing condition requirements
4.1 General requirements
4.1.1 Applicability
The requirements of this subclause (4.1) are general and apply to all viewing applications. Subclauses 4.2
through 4.4 contain additional requirements specific to a variety of viewing applications.
The specific viewing applications are
— conditions for critical comparison (P1, P3 and T1),
— conditions for practical appraisal of prints (P2 and P4), and
— conditions for viewing small transparencies by projection (T2)
NOTE 1 For ease of reference, each viewing condition described in this document has been given an alphanumeric
designation. This can be useful in describing or specifying conditions: e.g. "ISO 3664 viewing condition P2".
NOTE 2 The details of P1, P2, P3, P4, T1 and T2 are provided in 4.2.1, 4.3.1 and 4.4.1.
Print workflows are out of scope of this document however the following should be noted when selecting
measurement conditions M1 or M2 (ISO 13655) and corresponding viewing conditions. For print viewing,
if the amount of optical brightening agent in a substrate is small and its effect is negligible, M1 and M2
measurements will match, and print appearance will be the same under P1 and P3 or under P2 and P4
viewing conditions. Measurement of prints using M1 is consistent with P1 and P2 viewing conditions, and
measurement of prints using M2 is consistent with P3 and P4 viewing conditions. When prints with optical
brightening agents are viewed in environments with very little or no UV radiation, such as LED lamps that
typically emit very little UV, the P3 or P4 reference viewing conditions are most appropriate. When prints
with optical brightening agents are viewed in an environment that includes UV radiation of similar level to
that of D50, such as with natural daylight or D50 simulators that include UV, the P1 or P2 viewing conditions
are most appropriate.
NOTE 3 This guidance minimises differences between the reference viewing environment and intended viewing
environment for prints that fluoresce in the presence of UV. Where the intended viewing environment has a correlated
colour temperature that is substantially different from that of D50, there can be additional significant perceived
colour differences compared with all four reference viewing environments. These differences are further increased
where the lamps used in the intended viewing environment have poor colour fidelity or a CCT below 3 000 K.
4.1.2 Ambient conditions
The visual environment shall be designed to minimize interference with the viewing task. It is important to
eliminate extraneous conditions that affect the appraisal of prints or transparencies, and an observer should
avoid making judgements immediately after entering a new illumination environment because it takes a few
minutes to visually adapt fully to that new environment.
Extraneous light, whether from sources or reflected by objects and surfaces, should be baffled from view
and from illuminating the print, transparency, or other image being evaluated.
A viewing cabinet may be used to minimize the impact of any environmental illumination.
No strongly coloured surfaces (including clothing) should be visible in the viewing environment. In keeping
with the need to avoid visual distractions in the viewing field, equipment, controls and other objects should
be approximately neutral in colour. Displays used for press control should produce only grey-scale images
and their luminance should be limited to avoid distractions.
NOTE The presence of bright or strongly coloured objects within the viewing environment is a potential problem
because they can cause reflections affecting the colour appearance of the objects being assessed.

4.1.3 Viewing apparatus
To conform to this document, the values specified shall be achieved at the surface of viewing. The specified
relative spectral power distribution applies to the illuminated surface rather than to the source (or lamp)
because the light from the source may be modified by reflecting and transmitting components of the
apparatus, and the required relative spectral power distribution may be obtained from a mixture of light
from different sources.
The source, image being viewed, and observer's eyes shall be positioned to minimize the amount of light that
is reflected specularly toward the eyes of an observer on or near the normal to the centre of the viewing
surface.
When a viewing cabinet is used, the walls of the viewing cabinets shall be matte and neutral (C* ≤ 2,0 is
ab
required, and C* ≤ 1,5 is recommended) and the metric lightness (L*) shall be 80 or less and should be
ab
between 50 and 70. When making critical judgements on the details of a print, the light from the walls
can become a source of veiling flare. In those cases, a mid-grey of 20 % luminous reflectance (L* ≈ 50) is
recommended. The walls may be made even darker, but no lower than 16 of L*, if the suppression of gloss or
specular highlight are a concern. The use of dark walls less than 50 shall be noted in the report.
Since a table or a bottom of the viewing cabinet on which the sample is placed can become a surround, it
should conform to the surround specification in 4.2.4 for reflection viewing or 4.2.7 for transparency.
A viewing cabinet claiming compliance with this document shall clearly indicate the set of viewing conditions
(P1, P2, P3, P4) it meets and shall be accompanied by a report containing the results of the assessment of
the requirements listed in Table A.1 and A.2 as appropriate. A viewing cabinet providing multiple viewing
conditions shall explain how each viewing condition is achieved and should indicate the viewing condition
to which it is currently set.
4.1.4 Spectral conditions for the reference illuminant
The relative spectral power distribution of the reference illuminant for both prints and transparencies shall
1)
be based on CIE standard illuminant D50 as defined in CIE 15:2018 (see Table 5 of CIE 15:2018 ) including
or excluding UV. This represents a phase of natural daylight having a correlated colour temperature of
approximately 5 000 K. The chromaticity coordinates of CIE standard illuminant D50 are x = 0,347 7 and
y = 0,359 5 in the CIE 1964 chromaticity diagram and u' = 0,210 2 and v' = 0,488 9 in the CIE 1976
10 10 10
Uniform Chromaticity Scale (UCS) diagram.
The tristimulus values and chromaticity coordinates for the perfect reflecting diffuser, and the correlated
colour temperatures are given for the reference illuminant in Table 2.
NOTE 1 Chromaticity is specified here for the CIE 1964 standard colorimetric observer to ensure compatibility
with the method specified in ISO/CIE 23603 which is used to define the degree of conformance of the illumination to
the reference illuminant in 4.2.2.
Table 1 — Tristimulus values and chromaticity coordinates for the perfect reflecting diffuser and
the correlated colour temperature
D50/2° D50/10°
X 96,42 96,72
Y 100,00 100,00
Z 82,51 81,43
x 0,345 7 0,347 7
y 0,358 5 0,359 5
T 5 002 K —
c
u' — 0,210 2
v' — 0,488 9
1) The data table is available at https:// cie .co .at/ datatable/ cie -standard -illuminant -d50

ISO 36
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