ISO 3664:2000

INTERNATIONAL ISO
STANDARD 3664
Second edition
2000-09-01
Viewing conditions — Graphic technology
and photography
Conditions d'examen visuel — Technologie graphique et photographie
Reference number
ISO 3664:2000(E)
©
ISO 2000

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ISO 3664:2000(E)
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ISO 3664:2000(E)
Contents Page
Foreword . iii
Introduction . iv
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Viewing condition requirements .3
5 Test methods . 11
Annexes
A Summary of ISO viewing conditions specified in this International
Standard . 13
B Experimental data leading to selection of metameric indices and reference
illuminant for this International Standard . 14
C Guidelines for judging and exhibiting photographs . 19
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ISO 3664:2000(E)
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.
International Standards are drafted in accordance with the rules given in the
ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for voting. Publication as an International Standard requires
approval by at least 75% of the member bodies casting a vote.
Attention is drawn to the fact that some of the elements of this International
Standard may be the subject of patent rights. ISO shall not be held responsible for
identifying any or all such patent rights.
International Standard ISO 3664 was prepared jointly by Technical Committees
ISO/TC 42, Photography and ISO/TC 130, Graphic technology, with input from
ISO/TC 6, Paper, board and pulps.
This second edition cancels and replaces the first edition (ISO3664:1975) which
has been technically revised. This revision of the 1974 version of the International
Standard meets the current needs of the Graphic Technology and Photographic
industries and minimizes differences between viewing equipment. It should be
noted that this revision contains multiple specifications, each of which is
appropriate to specific requirements. Users should ensure that they employ the
specification which is appropriate to their application.

Annexes A to C of this International Standard are for information only.
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ISO 3664:2000(E)
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 should be noted
that the paper industry has its own set of International Standards for unprinted
paper which differ in illumination conditions from those recommended in this
International Standard.
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 may sensibly
agree to use this viewing condition for all evaluation and comparison. However, it
is important that this be properly agreed upon in advance and that it be 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 may be impractical to provide everybody in the production
chain with sufficiently consistent viewing apparatus. Since deficiencies in light
sources and viewing conditions, and inconsistencies between colour viewing
facilities, can distort the colour appearance of substrates, reproductions and
artwork, they are likely to cause miscommunication about colour reproduction and
processing. This International Standard 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 ultraviolet and visible spectrum to avoid distorting their
appearance from that observed under commonly used sources of illumination such
as daylight. The ultraviolet content is important where fluorescent samples, which
are excited in this region, are encountered; 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 the 1974 International Standard, as well as the majority
of equipment in current use, the reference spectral power distribution specified in
this International Standard is CIE Illuminant D . Many of the reasons for the
50
selection of illuminant D in 1974, as opposed to any other CIE daylight
50
illuminant, are equally applicable today. Much consideration was given to
changing the reference illuminant to be CIE F8, a 5 000 Kelvin illuminant more
typical of fluorescent lamps. However, it was felt that this would provide only a
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ISO 3664:2000(E)
minimal conformance advantage (as shown in informative annex B) and the actual
goal is for the illumination to simulate natural daylight.

Because it is very difficult to produce artificial sources of illumination which
closely match the spectral power distribution of daylight, it is important that the
tolerances specified within this International Standard provide a compromise
between that required for lamp manufacturing purposes and that for consistent
viewing. In this International Standard three constraints which define the colour of
the light falling on the viewing plane apply, one directly and two indirectly, and all
three must be met simultaneously if a viewing apparatus is to be in compliance.
The chromaticity, which directly defines the colour of the illumination at the
viewing surface, is specified as that for illuminant D and the tolerance by a circle
50
in the CIE 1976 Uniform Chromaticity Scale (UCS) diagram having a specified
radius around that value. To establish the compliance of the spectral power
distribution of the illumination to that of illuminant D the methods defined in
50
CIE Publications No. 13.3 and No. 51 are both specified. One defines the colour
rendering quality of a lamp; the other its ability to correctly predict metamers.
Both requirements are important to the graphic technology and photographic
industries.
Because CIE Publication No. 51 does not currently address illuminant D ,
50
additional virtual metamers for this illuminant, for both visible and ultraviolet
evaluation, were calculated and are defined in this International Standard. They
were derived from those published in CIE Publication No. 51 and are equivalent to
them. Also, based on experimental work described in annex B, a practical
tolerance of acceptability has been defined, alongside a Colour Rendering Index
requirement. (It should be noted that subsequent to the preparation of the final
draft of this International Standard, the CIE has prepared and published
Supplement 1 to CIE Publication 51 which incorporates the virtual metamers for
CIE illuminant D . The combination of CIE Publication 51 and Supplement 1 is
50
identified as CIE Publication 51.2-1999.)
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, ambient conditions, which may
affect the state of visual adaptation, need to be designed to avoid any significant
effects on the perception of colour and tone and immediate surround conditions
need to be specified also. Such specifications are provided in this International
Standard.
Experience in the industries covered by this International Standard 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 those under which it will be finally viewed.
This International Standard provides these two levels of illumination.
The higher level is essential to graphic technology where comparison is being
made; such as between original artwork and proof, or to evaluate small colour
differences between proof and press sheet in order to control a printing operation.
It is effective in these situations because it enhances the visibility of any
differences. The high level of illumination is also appropriate in photography
when comparing two, or more, transparencies or when critically evaluating a
single image to assess the darkest tones that can be printed.

Since, despite adaptation, the level of illumination has quite a significant effect on
the appearance of an image, the lower level is required in order to appraise the
image at a level more similar to that in which it will be finally viewed. Although
it is recognized that quite a wide range of illumination levels may be encountered
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ISO 3664:2000(E)
in practical viewing situations, the lower level chosen is considered to be fairly
representative of the range encountered. For this reason it is applicable to
aesthetic appraisal, including the conditions for routine inspection of prints.
The viewing of transparencies is specified both for direct viewing and by
projection.  Additional conditions are also specified for those conditions where
transparencies are to be compared to a print. The particular surround specified for
transparencies recognises the way that a transparency should 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.
The combination of surround and flare produce an appearance that is fairly
representative of how the transparency will look in a typically lighted room.
Small transparencies are commonly evaluated in graphic technology by direct
viewing. When it is necessary to view transparencies directly, they should 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 may be required which provides a magnified image when
viewed at an appropriate distance.
Colour monitors are increasingly being used to display and view digital images in
graphic technology and photography. In order to ensure consistency of assessment
in this situation it is important that the viewing conditions in which the monitors
are placed are reasonably well specified. However, it should be noted that
adherence to these specifications does not ensure that the monitor will match the
hardcopy without provision of a defined colour transformation to the displayed
image, or use of proper colour management. This aspect of matching is beyond
the scope of this International Standard. In practice, even with high quality colour
management, an accurate match is difficult to achieve because the luminance
levels generally differ significantly between hardcopy (print or transparency) and
softcopy (monitor).
Thus, it should be noted that the specifications for images viewed on colour
monitors, provided in this International Standard, are for images viewed
independently of any form of hardcopy; conditions for direct comparisons between
hardcopy and softcopy (even where a suitable colour transformation has been
applied) are beyond the scope of this International Standard which can be seen as
being primarily relevant where successive viewing of hardcopy and softcopy takes
place. ISO 12646, Graphic Technology - Colour proofing using a colour display,
currently at Working Draft level in TC 130, is being prepared to provide more
detailed recommendations where direct comparison is required. In general it may
be stated that for such comparisons it is desirable to view the colour monitor under
the lower levels of ambient illumination specified in this International Standard
and with the maximum level of luminance achievable, and the hardcopy sample at
the lower levels of illumination specified for printed matter in this International
Standard (and their equivalent for transparencies). However, it should be noted
that this will, in turn, affect the perceived tone and colourfulness of the hardcopy.
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INTERNATIONAL STANDARD ISO 3664:2000(E)
Viewing conditions — Graphic technology and photography
ISO 5-2:1991, Photography — Density measurements —
1 Scope
Part 2: Geometric conditions for transmission density.
This International Standard specifies viewing conditions
ISO 5-3:1995, Photography — Density measurements —
for images on both reflective and transmissive media, such
Part 3: Spectral conditions.
as prints (both photographic and photomechanical) and
transparencies, as well as images displayed in isolation on
ISO 5-4:1995, Photography — Density measurements —
colour monitors. Specifically, it shall be used for:
Part 4: Geometric conditions for reflection density.
— critical comparison between transparencies, reflection
1)
ISO 12646:____ , Graphic technology — Displays for
photographic or photomechanical prints and/or other
colour proofing — Characteristics and viewing conditions.
objects or images,

CIE Publication No. 13.3, 1995, Method of measuring and
— appraisal of the tone reproduction and colourfulness of
specifying the colour rendering properties of light sources,
prints and transparencies at illumination levels similar
2nd edition.
to those for practical use, including routine inspection,
CIE Publication No. 15.2, 1986, Colorimetry.
— critical appraisal of transparencies which are viewed
by projection, for comparison with prints, objects, or
CIE Publication No. 51, 1981, A method for assessing the
other reproductions, and
quality of daylight simulators for colorimetry.

— appraisal of images on colour monitors which are not
CIE Publication No. 17.4, 1987, International lighting
viewed in comparison to any form of hardcopy.
vocabulary.

This International Standard is not applicable to unprinted
papers.
3 Terms and definitions
For the purposes of this International Standard, the
2 Normative references
following terms and definitions apply.
The following normative documents contain provisions
3.1
which, through reference in this text, constitute provisions
chromaticity
of this International Standard. For dated references,
property of a colour stimulus defined by its chromaticity
subsequent amendments to, or revisions of, any of these
co-ordinates, or by its dominant or complementary
publications do not apply. However, parties to agreements
wavelength and purity taken together
based on the International Standard are encouraged to
[CIE Publication No. 17.4:1987, 845-03-34]
investigate the possibility of applying the most recent
editions of the normative documents indicated below. For
3.2
undated references, the latest editions of the normative
colour rendering index
document referred to applies. Members of IEC and ISO
measure of the degree to which the psychophysical colour
maintain registers of currently valid International
of an object illuminated by a test illuminant conforms to
Standards.
that of the same object illuminated by the reference
1) To be published.
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ISO 3664:2000(E)
illuminant, suitable allowance having been made for the
dφ
v
state of chromatic adaptation.
L '
v
dA×cosθ × dΩ
[CIE Publication No. 17.4:1987, 845-02-61]
3.3 where dN is the luminous flux transmitted by an
v
correlated colour temperature elementary beam passing through the given point and
temperature of the Planckian radiator whose perceived propagating in the solid angle dS containing the given
colour most closely resembles that of a given stimulus at direction; dA is the area of a section of that beam
the same brightness and under specified viewing containing the given point; 2 is the angle between the
conditions normal to that section and the direction of the beam
[CIE Publication No. 17.4:1987, 845-03-50] [CIE Publication No. 17.4:1987, 845-01-35]
3.4 3.10
flare off-press proof print
light falling on an image, in an imaging system, which print produced by a method other than press printing
does not emanate from the subject point whose purpose is to show the results of the colour
SEE image flare, veiling flare, and veiling glare. separation process in a way that closely simulates the
results on a production press
NOTE Veiling glare is also sometimes referred to as flare
3.11
3.5
on-press proof print
hardcopy
print produced by press printing (production or proof
representation of an image on a substrate which is self
press) whose purpose is to show the results of the colour
sustaining and reasonably permanent
separation process in a way that closely simulates the
SEE softcopy, print, and transparency
results on a production press
NOTE Examples include prints and transparencies.
3.12
original
3.6 illuminance
the scene or hardcopy from which image information is
quotient of the luminous flux
obtained, using an image capture device, in a reproduction
incident on an element of the surface containing the point
process
by the area of that element
[CIE Publication No. 17.4:1987, 845-01-38] NOTE 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
3.7
term original scene is sometimes used.
illuminant

radiation with a relative spectral power distribution
3.13
defined over the wavelength range that influences object-
print
colour perception
two-dimensional hardcopy form of an image intended for
[CIE Publication No. 17.4:1987, 845-03-10]
viewing

SEE hardcopy, softcopy, transparency
3.8
image flare
NOTE In still photography and graphic technology, the term
light from a subject point that is scattered by the optical
print is reserved for reflection hardcopy; a medium designed to
system to areas of the image plane other than the
be viewed by reflected light.
appropriate image point
3.14
NOTE The distribution of image-flare light resulting from any
relative spectral power distribution
subject point is specified by the image point spread function.
ratio of the spectral power distribution of a source or
Point spread functions tend to fall off rapidly as the distance
illuminant to a fixed reference value which can be an
from the image point is increased, are variable for different
image-point locations and are typically not radially symmetric average value, a maximum value, or an arbitrarily chosen
for image points some distance from the optical system axis.
value of this distribution.
3.9
3.15
luminance (in a given direction, at a given point of a
softcopy
real or imaginary surface)
representation of an image produced using a device
quantity defined by the formula:
capable of directly representing different digital images in
succession and in a non-permanent form
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ISO 3664:2000(E)
EXAMPLE the most common example is a monitor samples, which provide metameric matches for specific
SEE hardcopy standard daylight illuminants.
NOTE Virtual metamers are used to test and classify
3.16
illumination sources which simulate daylight according to the
source
method provided in CIE Publication No. 51. This classification
primary emitter of electromagnetic radiation
is accomplished by calculating the average of the colour
differences obtained for these metamers between the
3.17
illumination source in question and a CIE standard illuminant.
surround
Although it may be possible to construct physical realizations of
area adjacent to the border of an image which, upon
some virtual metamers, the fact that they may not be real allows
viewing the image, may affect the local state of adaptation
greater flexibility in their design.
of the eye
NOTE The surround, which can have a significant effect on the
4 Viewing condition requirements
perceived tone and colour reproduction of an image, should not
be confused with any border immediately surrounding the
4.1 General requirements
image, such as any unprinted white substrate for reflection copy
or the unexposed border present on many transparencies. For a
colour monitor, the border will normally be dark grey or black, In this clause, the requirements that apply to all of the
and hence the same as the surround. However, when simulating
specified viewing conditions are stated. The requirements
hardcopy it will be similar to that hardcopy, both in terms of
specific to each of these viewing conditions are defined in
lightness and width.
4.2 (Critical comparison), 4.3 (Practical appraisal of

prints) and 4.4 (Projection viewing of small
3.18
transparencies).
transparency
two-dimensional hardcopy form of an image designed to
NOTE For ease of reference, each viewing condition described
be viewed by transmitted light
in the International Standard has been given an alpha-numeric
SEE hardcopy, softcopy, print designation. This may be useful in describing or specifying
conditions: e.g. ISO viewing condition P2 as specified in this
International Standard.
3.19
transparency illuminator
4.1.1 Viewing apparatus
apparatus used for back illumination of a transparency
To comply with this International Standard, the values
3.20
specified shall be achieved at the surface of viewing. The
veiling flare
specified relative spectral power distribution applies to the
relatively uniform but unwanted irradiation in the image
illuminated surface rather than to the source (or lamp)
plane of an optical system, caused by the scattering and
because the light from the source may be modified by
reflection of a proportion of the radiation which enters the
reflecting and transmitting components of the apparatus,
system through its normal entrance aperture where the
and the required relative spectral power distribution may
radiation may be from inside or outside the field of view
be obtained from a mixture of light from different sources.
of the system
The source, image being viewed, and observer's eyes shall
NOTE Light leaks in an optical system housing can cause
additional unwanted irradiation of the image plane. This be positioned to minimize the amount of light specularly
irradiation may resemble veiling flare. reflected toward the eyes of an observer on or near the

normal to the centre of the viewing surface.
3.21
veiling glare
The surround of a print or transparency shall have a
light falling on a radiant image surface, such as a back
diffusing surface and shall have a CIELAB chroma value
illuminated transparency or monitor, which adds to the
no greater than 2; i.e. shall appear neutral.
luminance of the image
4.1.2 Spectral conditions for the reference illuminant
NOTE Veiling glare lightens and reduces the apparent contrast
of the darker parts of an image. It differs from veiling flare in
The relative spectral power distribution of the reference
that it is used exclusively for the perception of images in which
illuminant for both prints and transparencies shall be CIE
no entrance aperture is defined.
illuminant D as defined in CIE 15.2 (see Table 1). This
50
represents a phase of natural daylight having a correlated
3.22
colour temperature of approximately 5 000 K. The
virtual metamer
chromaticity coordinates of illuminant D are x =
50 10
set of spectral radiance factors, not based on physical
0,347 8 and y = 0,359 5 in the CIE chromaticity diagram
10
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ISO 3664:2000(E)
Table 1 — Relative spectral power of reference illuminant D .
50
Wavelength Relative power for Wavelength Relative power for
nm illuminant D nm illuminant D
50 50
300 0,02 550 102,32
305 1,03 555 101,16
310 2,05 560 100,00
315 4,91 565 98,87
320 7,78 570 97,74
325 11,26 575 98,33
330 14,75 580 98,92
335 16,35 585 96,21
340 17,95 590 93,50
345 19,48 595 95,59
350 21,01 600 97,69
355 22,48 605 98,48
360 23,94 610 99,27
365 25,45 615 99,16
370 26,96 620 99,04
375 25,72 625 97,38
380 24,49 630 95,72
385 27,18 635 97,29
390 29,87 640 98,86
395 39,59 645 97,26
400 49,31 650 95,67
405 52,91 655 96,93
410 56,51 660 98,19
415 58,27 665 100,60
420 60,03 670 103,00
425 58,93 675 101,07
430 57,82 680 99,13
435 66,32 685 93,26
440 74,82 690 87,38
445 81,04 695 89,49
450 87,25 700 91,60
455 88,93 705 92,25
460 90,61 710 92,89
465 90,99 715 84,87
470 91,37 720 76,85
475 93,24 725 81,68
480 95,11 730 86,51
485 93,54 735 89,55
490 91,96 740 92,58
495 93,84 745 85,40
500 95,72 750 78,23
505 96,17 755 67,96
510 96,61 760 57,69
515 96,87 765 70,31
520 97,13 770 82,92
525 99,61 775 80,60
530 102,10 780 78,27
535 101,43
540 100,75
545 101,54
NOTE The wavelength specification has been extended beyond the normal visual range because of the need to consider brighteners or
dyes which may fluoresce.
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ISO 3664:2000(E)
and u' = 0,210 2 and v' = 0,488 9 in the CIE 1976 mechanism for indicating degradation.
10 10
Uniform Chromaticity Scale (UCS) diagram.
However, it is the responsibility of the user, both before
NOTE Chromaticity is specified for the CIE 1964 standard
and beyond this time limit, to undertake measurements as
colorimetric observer to ensure compatibility with the method
specified in clause 5 to ensure compliance, unless it can be
specified in CIE Publication No. 51 which is used to define the
otherwise demonstrated that the equipment remains within
degree of compliance of the illumination to the reference
tolerance.
illuminant in 4.2.2.
4.2 Conditions for critical comparison (ISO
4.1.3 Colour rendering index
viewing conditions P1 and T1)
The CIE general colour rendering index of the viewing
4.2.1 Applicability
surface shall be measured as specified in CIE Publication
No. 13.3 and shall have a value of 90 or higher. In
This subclause specifies viewing conditions for the critical
addition, the separate special colour rendering indices for
comparison between two (or more) copies of an image.
samples 1 to 8 as specified in CIE Publication No. 13.3
The co
...