SIST ISO 12646:2005
(Main)Graphic technology -- Displays for colour proofing -- Characteristics and viewing conditions
Graphic technology -- Displays for colour proofing -- Characteristics and viewing conditions
ISO 12646:2004 specifies requirements for uniformity, size, resolution, convergence, refresh rate, luminance levels and viewing conditions for a colour display used to simulate a hard copy proofing system.
Technologie graphique -- Affichages pour la réalisation d'épreuves en couleur -- Caractéristiques et conditions d'examen visuel
Grafična tehnologija - Zasloni za barvno preskušanje - Značilnosti in pogoji za vizualno opazovanje
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INTERNATIONAL ISO
STANDARD 12646
First edition
2004-04-01
Graphic technology — Displays for
colour proofing — Characteristics and
viewing conditions
Technologie graphique — Affichages pour la réalisation d'épreuves en
couleur — Caractéristiques et conditions d'examen visuel
Reference number
ISO 12646:2004(E)
©
ISO 2004
---------------------- Page: 1 ----------------------
ISO 12646:2004(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2004
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2004 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 12646:2004(E)
Contents Page
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Requirements . 2
4.1 Resolution. 2
4.2 Size . 2
4.3 Refresh rate . 2
4.4 Uniformity . 2
4.5 Geometric accuracy. 2
4.6 Convergence . 2
4.7 Ambient illumination conditions . 2
4.8 Chromaticity and luminance of the white and black points and tracking (channel balance) . 3
4.9 Opto-electronic transfer function. 3
5 Test methods. 4
5.1 Resolution. 4
5.2 Uniformity . 5
5.3 Geometric accuracy. 5
5.4 Convergence . 6
5.5 White-point and Black-point chromaticity and luminance . 6
5.6 Opto-electronic transfer function and tracking . 7
Annex A (informative) Characterization and calibration . 8
Bibliography . 12
© ISO 2004 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 12646:2004(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 2.
The main task of technical committees is to prepare International Standards. 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 possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 12646 was prepared by Technical Committee ISO/TC 130, Graphic technology.
iv © ISO 2004 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 12646:2004(E)
Introduction
The ability to match colour images displayed on colour monitors to the images produced when the same
digital file is rendered by proofing and printing systems (commonly referred to as “soft” proofing) is
increasingly expected in graphic arts. Obtaining such a match is not simple and to be fully accurate requires
careful control of many aspects of the process. The primary purpose of this International Standard is to make
recommendations with respect to the soft proof viewing conditions. If these are controlled it is then possible for
users to exchange meaningful calibration and characterization data such that a consistent and, possibly,
accurate colour match to the hard copy proof is achieved; see Annex A. (Calibration is the operation to
establish that the measured values agree with the values specified by a standard, or a characterization
process; characterization is the process of relating device-dependent colour values to device-independent
colour values. In the case of visual display devices, the RGB device values are related to CIE tristimulus
values.)
This International Standard is primarily based on the needs of Cathode-Ray Tube display technology, but it is
anticipated that many of the recommendations will be appropriate to newer display technologies.
The appearance of a colour image on a colour display is influenced by many physical factors other than
controlled ambient viewing conditions. Amongst the most important of these are uniformity, convergence, size
and resolution (in order to permit rendition of the proof at close to its normal size and with the finest detail
visible on the hard copy at normal viewing distances), freedom from flicker, the opto-electronic calibration of
the display and the settings of its display-driver software. So, to be acceptable as a proofing system which
provides a reasonable level of image quality, the display must also exhibit acceptable quality of these
properties. This International Standard specifies the minimum requirements for factors such as uniformity,
convergence, refresh rate, size and spatial resolution. However, since these parameters are subject to
improvement as display technology changes, this International Standard should be seen as defining minimum
requirements for these parameters. It is assumed that displays used for this purpose will always conform to
accepted industry “standards” for Computer-Aided Design (CAD), and generally provide quality levels
considered acceptable for this purpose, where they offer an improvement over the specifications herein.
It should be noted that, even for displays of the highest quality, the appearance of the displayed image will be
limited by the accuracy of the colour transformation used for converting the digital file from its encoded colour
space to that required for display purposes. This International Standard provides no formal specifications for
these transforms, although the issues are discussed in an informative annex, together with recommendations
for achieving an acceptable colour transformation.
It should be noted that this International Standard only considers the setting up of colour displays as “soft”
proofing devices. It is primarily directed at applications where the displayed image will be directly compared to
a hard copy. It is therefore concerned with modifying the “hard” and “soft” controls of the display to enable it to
simulate a proof. In this sense, it can be looked on as a “slave” device. However, it is in the interests of a CAD
user, where the colour display in a real sense “originates” the image, to set the display up in a similar way.
This will enable simpler optimization of the colour transformation to the selected hard-copy system used for
rendering the image in order to produce an accurate reproduction, if this is an important requirement. However,
it is possible to undertake image processing to modify the image when rendered to make it look like the
displayed image (colour gamuts permitting), whatever the opto-electronic calibration of the display. This is
briefly discussed in Annex A.
Users of this International Standard also need to be familiar with CIE Publication 122. Those unfamiliar with
[6]
the judgement of displays may also find it helpful to read International Standard IEC 1223-2-5 which
contains much useful detailed information about evaluation and testing of image display devices.
© ISO 2004 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 12646:2004(E)
Graphic technology — Displays for colour proofing —
Characteristics and viewing conditions
1 Scope
This International Standard specifies requirements for uniformity, size, resolution, convergence, refresh rate,
luminance levels and viewing conditions for a colour display used to simulate a hard copy proofing system.
NOTE This International Standard has been produced with regard to CRT displays, which was by far the dominant
technology in use at the time of preparation. However, displays using other technologies are expected to at least meet the
minimum of the specifications provided herein.
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 3664, Viewing conditions — Graphic technology and photography
CIE Publication 15, Colorimetry
CIE Publication 122, The relationship between digital and colorimetric data for computer controlled CRT
displays
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
convergence
ability of the three electron beams (R, G and B) to come together at a single spot on the surface of the CRT
3.2
gamma
〈display〉 exponent of a power law relationship between amplified video voltages and beam currents
[adapted from CIE Publication 122]
3.3
hard-copy proofing system
system for simulating a printed image using a printing device which may be different from that used for
production
3.4
opto-electronic transfer function
relationship between the input values provided to, and the luminance values produced by, a display device
© ISO 2004 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 12646:2004(E)
3.5
refresh rate
frequency with which the image on the screen is redrawn
NOTE The refresh rate is expressed in hertz.
3.6
tracking
the process (by adjustment of the amplifiers) of ensuring that the relationship between the three channels of a
display balance, so that for all levels equal values in each channel produce a neutral sensation
4 Requirements
4.1 Resolution
The display resolution shall be sufficient to display an image of 1 280 × 1 024 pixels without interpolation.
When a test image with dimensions as defined in 5.1 is displayed, all specified lines shall be visible at a
normal viewing distance (defined as 0,5 m for the purposes of this International Standard).
4.2 Size
The display shall be capable of displaying an image having a diagonal measurement of at least 43 cm and a
height of at least 22 cm.
4.3 Refresh rate
The CRT display shall have a refresh rate of at least 80 Hz, non-interlaced.
4.4 Uniformity
The display should be visually uniform when displaying flat white, grey and black images. When measured as
described in 5.2, all luminance values should be within 5 % of the luminance of the centre and shall be within
10 % of it. However, there should not be areas of significant visual non-uniformity between these areas.
NOTE Uniformity of chromaticity is described in 4.8.
4.5 Geometric accuracy
When displaying the grid pattern defined in 5.3, the display should essentially be free of distortion. The length
of adjacent lines of the grid pattern shall be within 2 mm of each other and no line length shall deviate by more
than 2,5 mm from the mean length.
4.6 Convergence
When displaying the grid pattern defined in 5.3, all lines shall appear wholly free of colour fringing within the
central region (defined as the area within half the linear diagonal distance). A small amount of fringing may be
accepted outside of this area but is not recommended.
4.7 Ambient illumination conditions
Although the ambient illumination conditions specified in this subclause are consistent with those of ISO 3664,
it is important to note that the specification of that International Standard is intended for viewing displayed
images independently of any hard copy. For the purposes of this International Standard, in which comparison
to hard copy is assumed, a more restrictive illumination condition is required. Thus, a lower level of ambient
illumination, with a more restrictive colour temperature and surround condition than that in ISO 3664, is
2 © ISO 2004 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 12646:2004(E)
specified. An additional constraint beyond those of ISO 3664 is added to ensure that any reflected glare from
the front surface of the display does not significantly reduce the perceived contrast.
This subclause requires the following.
The level of illumination, when measured at the face of the monitor or in any plane between the monitor
and the observer, shall be less than 32 lx.
The surround shall be no more than 10 % of the maximum luminance of the screen.
The colour temperature of the ambient illumination shall approximate D50 (particularly if the level of
ambient illumination is towards the high end of the specification).
The level of illumination, when viewing a black screen (i.e., an image defined as R = G = B = 0), shall be
less than 5 % of that obtained when viewing a white screen (i.e., an image defined as R = G = B = 255)
as measured at the plane of the observer.
4.8 Chromaticity and luminance of the white and black points and tracking (channel
balance)
At the centre of the white image defined in 5.2, the chromaticity of the display should be set to that of D50;
namely u’ = 0,209 2, v’ = 0,488 1 (as defined in CIE Publication 15). The chromaticity obtained shall be within
a circle of radius 0,005 from this point. The chromaticity shall also be measured at the other points shown in
Figure 2 and must be within 0,01 of the chromaticity of D50.
2
The luminance level should be as high as practical but shall be at least 80 cd/m and should be at least
2
120 cd/m .
NOTE 1 It is important to insure that the display driver look-up tables be loaded to achieve this specification.
NOTE 2 It is important to take care not to set the display at luminance levels higher than that recommended by the
manufacturer.
The black point shall have a luminance that is less than 1 % of the maximum luminance (i.e., a luminance
ratio of at least 100 to 1).
NOTE The dynamic range of the monitor (black to white) specified in this subclause is higher than that specified in
4.7. This is because it is assumed that measurement of the luminance of the black of the display will be made in contact,
thereby avoid the viewing flare defined in 4.7.
At the centre of the display, the chromaticity of any neutral image (defined by equal digital values for R, G, and
B) should be within a radius of 0,005 (in u’, v’) from the chromaticity of the white. However, the chromaticity
tolerance may increase linearly with decreasing luminance such that at 10 % of the maximum luminance it
shall be within a circle of radius 0,03 of the chromaticity of the white point. It is for this luminance that the
individual channel offsets should be adjusted where possible.
4.9 Opto-electronic transfer function
The gamma of a CRT display should be in the range 2 to 2,4 for each channel. This shall be measured as
described in 5.5. The procedure for defining offset and gain is specified in 5.6.
For device technology other than CRTs, the gamma function may be very different from this simple power
function. The display driver look-up tables should be loaded to achieve this specification.
NOTE The term gamma has been used here as defined in CIE Publication 122. As such, it is being used in a quite
unambiguous way and, together with the offset and gain, it provides the opto-electronic transfer function of the CRT
display. However, traditionally in graphic technology, gamma was often defined as the “best fit” exponent when ignoring
offset and gain. It is important not to confuse this usage with the definition here. Some standards (such as
[7]
IEC 61966-2-1 ) go further and suggest that, since the term has been used in various ways, it is preferable not to use it
© ISO 2004 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 12646:2004(E)
at all to avoid possible ambiguity. Those requiring further information on this subject are referred to CIE Publication 122
[8]
and to the paper by Anderson et al . The latter paper includes explanation of some of the terms that have been in
common use (including system gamma, monitor gamma and encoding gamma) and how they relate to the definition in
CIE Publication 122.
5 Test methods
5.1 Resolution
A test image, consisting of a number of fields, each composed of white and black lines of varying frequency as
shown in Figure 1 a), shall be displayed in various positions and orientations as shown in Figure 1 b). The
lines and spaces are equal in width for each field and range from 0,5 mm to 0,2 mm in intervals of 0,05 mm.
When viewed normally, and at a typical viewing distance (approximately 0,5 m), the lines labelled D (which
have a spacing of 0,35 mm) shall be clearly distinguishable, and those labelled F (which have a spacing of
0,25 mm) should be clearly distinguishable, for all images within the central region of the display. (The central
region is defined as that within half the linear diagonal distance.) Any images outside of this region may have
a resolution poorer by 0,05 mm.
It is assumed that the observer making this assessment has reasonable vision (though possibly aided by
spectacles). No additional magnifier should be used.
Figure 1 — Resolution targets (a) and layout of the resolution targets (b)
4 © ISO 2004 – All rights reserved
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ISO 12646:2004(E)
5.2 Uniformity
The uniformity shall be determined for white, grey and black images that each fills the screen. The white
image shall consist of the maximum value in each of the Red, Green and Blue channels (255 for an 8-bit
display).
The neutrality and luminance level of the grey image and black image is not critical. However, as a guide, the
grey image should consist of approximately half of the maximum value in each channel (127 for an 8-bit
display), and the black should consist of approximately a quarter of the maximum value in each channel (63
for an 8-bit display).
For each level, 9 points of the image area of the screen shall be measured as shown in Figure 2.
Measurements shall be made using a photometer or radiometer,
...
SLOVENSKI STANDARD
SIST ISO 12646:2005
01-januar-2005
*UDILþQDWHKQRORJLMD=DVORQL]DEDUYQRSUHVNXãDQMH=QDþLOQRVWLLQSRJRML]D
YL]XDOQRRSD]RYDQMH
Graphic technology -- Displays for colour proofing -- Characteristics and viewing
conditions
Technologie graphique -- Affichages pour la réalisation d'épreuves en couleur --
Caractéristiques et conditions d'examen visuel
Ta slovenski standard je istoveten z: ISO 12646:2004
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
37.100.10 Reprodukcijska oprema Reproduction equipment
SIST ISO 12646:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 12646:2005
---------------------- Page: 2 ----------------------
SIST ISO 12646:2005
INTERNATIONAL ISO
STANDARD 12646
First edition
2004-04-01
Graphic technology — Displays for
colour proofing — Characteristics and
viewing conditions
Technologie graphique — Affichages pour la réalisation d'épreuves en
couleur — Caractéristiques et conditions d'examen visuel
Reference number
ISO 12646:2004(E)
©
ISO 2004
---------------------- Page: 3 ----------------------
SIST ISO 12646:2005
ISO 12646:2004(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2004
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2004 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 12646:2005
ISO 12646:2004(E)
Contents Page
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Requirements . 2
4.1 Resolution. 2
4.2 Size . 2
4.3 Refresh rate . 2
4.4 Uniformity . 2
4.5 Geometric accuracy. 2
4.6 Convergence . 2
4.7 Ambient illumination conditions . 2
4.8 Chromaticity and luminance of the white and black points and tracking (channel balance) . 3
4.9 Opto-electronic transfer function. 3
5 Test methods. 4
5.1 Resolution. 4
5.2 Uniformity . 5
5.3 Geometric accuracy. 5
5.4 Convergence . 6
5.5 White-point and Black-point chromaticity and luminance . 6
5.6 Opto-electronic transfer function and tracking . 7
Annex A (informative) Characterization and calibration . 8
Bibliography . 12
© ISO 2004 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 12646:2005
ISO 12646:2004(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 2.
The main task of technical committees is to prepare International Standards. 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 possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 12646 was prepared by Technical Committee ISO/TC 130, Graphic technology.
iv © ISO 2004 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 12646:2005
ISO 12646:2004(E)
Introduction
The ability to match colour images displayed on colour monitors to the images produced when the same
digital file is rendered by proofing and printing systems (commonly referred to as “soft” proofing) is
increasingly expected in graphic arts. Obtaining such a match is not simple and to be fully accurate requires
careful control of many aspects of the process. The primary purpose of this International Standard is to make
recommendations with respect to the soft proof viewing conditions. If these are controlled it is then possible for
users to exchange meaningful calibration and characterization data such that a consistent and, possibly,
accurate colour match to the hard copy proof is achieved; see Annex A. (Calibration is the operation to
establish that the measured values agree with the values specified by a standard, or a characterization
process; characterization is the process of relating device-dependent colour values to device-independent
colour values. In the case of visual display devices, the RGB device values are related to CIE tristimulus
values.)
This International Standard is primarily based on the needs of Cathode-Ray Tube display technology, but it is
anticipated that many of the recommendations will be appropriate to newer display technologies.
The appearance of a colour image on a colour display is influenced by many physical factors other than
controlled ambient viewing conditions. Amongst the most important of these are uniformity, convergence, size
and resolution (in order to permit rendition of the proof at close to its normal size and with the finest detail
visible on the hard copy at normal viewing distances), freedom from flicker, the opto-electronic calibration of
the display and the settings of its display-driver software. So, to be acceptable as a proofing system which
provides a reasonable level of image quality, the display must also exhibit acceptable quality of these
properties. This International Standard specifies the minimum requirements for factors such as uniformity,
convergence, refresh rate, size and spatial resolution. However, since these parameters are subject to
improvement as display technology changes, this International Standard should be seen as defining minimum
requirements for these parameters. It is assumed that displays used for this purpose will always conform to
accepted industry “standards” for Computer-Aided Design (CAD), and generally provide quality levels
considered acceptable for this purpose, where they offer an improvement over the specifications herein.
It should be noted that, even for displays of the highest quality, the appearance of the displayed image will be
limited by the accuracy of the colour transformation used for converting the digital file from its encoded colour
space to that required for display purposes. This International Standard provides no formal specifications for
these transforms, although the issues are discussed in an informative annex, together with recommendations
for achieving an acceptable colour transformation.
It should be noted that this International Standard only considers the setting up of colour displays as “soft”
proofing devices. It is primarily directed at applications where the displayed image will be directly compared to
a hard copy. It is therefore concerned with modifying the “hard” and “soft” controls of the display to enable it to
simulate a proof. In this sense, it can be looked on as a “slave” device. However, it is in the interests of a CAD
user, where the colour display in a real sense “originates” the image, to set the display up in a similar way.
This will enable simpler optimization of the colour transformation to the selected hard-copy system used for
rendering the image in order to produce an accurate reproduction, if this is an important requirement. However,
it is possible to undertake image processing to modify the image when rendered to make it look like the
displayed image (colour gamuts permitting), whatever the opto-electronic calibration of the display. This is
briefly discussed in Annex A.
Users of this International Standard also need to be familiar with CIE Publication 122. Those unfamiliar with
[6]
the judgement of displays may also find it helpful to read International Standard IEC 1223-2-5 which
contains much useful detailed information about evaluation and testing of image display devices.
© ISO 2004 – All rights reserved v
---------------------- Page: 7 ----------------------
SIST ISO 12646:2005
---------------------- Page: 8 ----------------------
SIST ISO 12646:2005
INTERNATIONAL STANDARD ISO 12646:2004(E)
Graphic technology — Displays for colour proofing —
Characteristics and viewing conditions
1 Scope
This International Standard specifies requirements for uniformity, size, resolution, convergence, refresh rate,
luminance levels and viewing conditions for a colour display used to simulate a hard copy proofing system.
NOTE This International Standard has been produced with regard to CRT displays, which was by far the dominant
technology in use at the time of preparation. However, displays using other technologies are expected to at least meet the
minimum of the specifications provided herein.
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 3664, Viewing conditions — Graphic technology and photography
CIE Publication 15, Colorimetry
CIE Publication 122, The relationship between digital and colorimetric data for computer controlled CRT
displays
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
convergence
ability of the three electron beams (R, G and B) to come together at a single spot on the surface of the CRT
3.2
gamma
〈display〉 exponent of a power law relationship between amplified video voltages and beam currents
[adapted from CIE Publication 122]
3.3
hard-copy proofing system
system for simulating a printed image using a printing device which may be different from that used for
production
3.4
opto-electronic transfer function
relationship between the input values provided to, and the luminance values produced by, a display device
© ISO 2004 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST ISO 12646:2005
ISO 12646:2004(E)
3.5
refresh rate
frequency with which the image on the screen is redrawn
NOTE The refresh rate is expressed in hertz.
3.6
tracking
the process (by adjustment of the amplifiers) of ensuring that the relationship between the three channels of a
display balance, so that for all levels equal values in each channel produce a neutral sensation
4 Requirements
4.1 Resolution
The display resolution shall be sufficient to display an image of 1 280 × 1 024 pixels without interpolation.
When a test image with dimensions as defined in 5.1 is displayed, all specified lines shall be visible at a
normal viewing distance (defined as 0,5 m for the purposes of this International Standard).
4.2 Size
The display shall be capable of displaying an image having a diagonal measurement of at least 43 cm and a
height of at least 22 cm.
4.3 Refresh rate
The CRT display shall have a refresh rate of at least 80 Hz, non-interlaced.
4.4 Uniformity
The display should be visually uniform when displaying flat white, grey and black images. When measured as
described in 5.2, all luminance values should be within 5 % of the luminance of the centre and shall be within
10 % of it. However, there should not be areas of significant visual non-uniformity between these areas.
NOTE Uniformity of chromaticity is described in 4.8.
4.5 Geometric accuracy
When displaying the grid pattern defined in 5.3, the display should essentially be free of distortion. The length
of adjacent lines of the grid pattern shall be within 2 mm of each other and no line length shall deviate by more
than 2,5 mm from the mean length.
4.6 Convergence
When displaying the grid pattern defined in 5.3, all lines shall appear wholly free of colour fringing within the
central region (defined as the area within half the linear diagonal distance). A small amount of fringing may be
accepted outside of this area but is not recommended.
4.7 Ambient illumination conditions
Although the ambient illumination conditions specified in this subclause are consistent with those of ISO 3664,
it is important to note that the specification of that International Standard is intended for viewing displayed
images independently of any hard copy. For the purposes of this International Standard, in which comparison
to hard copy is assumed, a more restrictive illumination condition is required. Thus, a lower level of ambient
illumination, with a more restrictive colour temperature and surround condition than that in ISO 3664, is
2 © ISO 2004 – All rights reserved
---------------------- Page: 10 ----------------------
SIST ISO 12646:2005
ISO 12646:2004(E)
specified. An additional constraint beyond those of ISO 3664 is added to ensure that any reflected glare from
the front surface of the display does not significantly reduce the perceived contrast.
This subclause requires the following.
The level of illumination, when measured at the face of the monitor or in any plane between the monitor
and the observer, shall be less than 32 lx.
The surround shall be no more than 10 % of the maximum luminance of the screen.
The colour temperature of the ambient illumination shall approximate D50 (particularly if the level of
ambient illumination is towards the high end of the specification).
The level of illumination, when viewing a black screen (i.e., an image defined as R = G = B = 0), shall be
less than 5 % of that obtained when viewing a white screen (i.e., an image defined as R = G = B = 255)
as measured at the plane of the observer.
4.8 Chromaticity and luminance of the white and black points and tracking (channel
balance)
At the centre of the white image defined in 5.2, the chromaticity of the display should be set to that of D50;
namely u’ = 0,209 2, v’ = 0,488 1 (as defined in CIE Publication 15). The chromaticity obtained shall be within
a circle of radius 0,005 from this point. The chromaticity shall also be measured at the other points shown in
Figure 2 and must be within 0,01 of the chromaticity of D50.
2
The luminance level should be as high as practical but shall be at least 80 cd/m and should be at least
2
120 cd/m .
NOTE 1 It is important to insure that the display driver look-up tables be loaded to achieve this specification.
NOTE 2 It is important to take care not to set the display at luminance levels higher than that recommended by the
manufacturer.
The black point shall have a luminance that is less than 1 % of the maximum luminance (i.e., a luminance
ratio of at least 100 to 1).
NOTE The dynamic range of the monitor (black to white) specified in this subclause is higher than that specified in
4.7. This is because it is assumed that measurement of the luminance of the black of the display will be made in contact,
thereby avoid the viewing flare defined in 4.7.
At the centre of the display, the chromaticity of any neutral image (defined by equal digital values for R, G, and
B) should be within a radius of 0,005 (in u’, v’) from the chromaticity of the white. However, the chromaticity
tolerance may increase linearly with decreasing luminance such that at 10 % of the maximum luminance it
shall be within a circle of radius 0,03 of the chromaticity of the white point. It is for this luminance that the
individual channel offsets should be adjusted where possible.
4.9 Opto-electronic transfer function
The gamma of a CRT display should be in the range 2 to 2,4 for each channel. This shall be measured as
described in 5.5. The procedure for defining offset and gain is specified in 5.6.
For device technology other than CRTs, the gamma function may be very different from this simple power
function. The display driver look-up tables should be loaded to achieve this specification.
NOTE The term gamma has been used here as defined in CIE Publication 122. As such, it is being used in a quite
unambiguous way and, together with the offset and gain, it provides the opto-electronic transfer function of the CRT
display. However, traditionally in graphic technology, gamma was often defined as the “best fit” exponent when ignoring
offset and gain. It is important not to confuse this usage with the definition here. Some standards (such as
[7]
IEC 61966-2-1 ) go further and suggest that, since the term has been used in various ways, it is preferable not to use it
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at all to avoid possible ambiguity. Those requiring further information on this subject are referred to CIE Publication 122
[8]
and to the paper by Anderson et al . The latter paper includes explanation of some of the terms that have been in
common use (including system gamma, monitor gamma and encoding gamma) and how they relate to the definition in
CIE Publication 122.
5 Test methods
5.1 Resolution
A test image, consisting of a number of fields, each composed of white and black lines of varying frequency as
shown in Figure 1 a), shall be displayed in various positions and orientations as shown in Figure 1 b). The
lines and spaces are equal in width for each field and range from 0,5 mm to 0,2 mm in intervals of 0,05 mm.
When viewed normally, and at a typical viewing distance (approximately 0,5 m), the lines labelled D (which
have a spacing of 0,35 mm) shall be clearly distinguishable, and those labelled F (which have a spacing of
0,25 mm) should be clearly distinguishable, for all images within the central region of the display. (The central
region is defined as that within half the linear diagonal distance.) Any images outside of this region may have
a resolution poorer by 0,05 mm.
It is assumed that the observer making this assessment has reasonable vision (though possibly aided by
spectacles). No additional magnifier should be used.
Figure 1 — Resolution targets (a) and layout of the resolution targets (b)
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5.2 Uniformity
The uniformity shall be determined for white, grey and black images that each fills the screen. The white
image shall consist of the maximum value in each of the Red, Green and Blue channels (255 for an 8-bit
display).
The neutrality and luminance level of the grey image and black image is not critical. However, as a guide, the
grey image should consist of approximately half of the maximum value in each channel (127 for an 8-bit
display), and the black should consist of approximately a quarter of the maximum value in each channel (63
for an 8-bit display).
For each level, 9 points of the image area of the screen shall be measured as shown in Figure 2.
Measurements shall be made using a photometer or radiometer, as specified in 5.5.
Key
h height of display
b width of display
Figure 2 — Positions for the measurement of uniformity
5.3 Geometric accuracy
Geometric accuracy shall be evaluated using the test pattern shown in Figure 3 (derived from that shown in
[6]
IEC 1223-2-5 ). This pattern shall be displayed as black on white, shall have at least 11 lines and no more
than 17 lines in both horizontal and vertical orientations (preferably an odd number), and the lines shall be
2 display pixels wide. All lines shall be of the same length. The pattern shall have an identifiable outer
boundary to ensure accurate positioning of the pattern on the display and shall contain the circle inscribed
within the boundary to aid the visual assessment. The pattern should be assessed according to the following
[6]
procedure derived from that given in IEC 1223-2-5 .
Visually assess the boundary pattern to ensure it is all present.
Visually assess the circle for distortion, which should be negligible.
Measure the lengths of the lines.
NOTE Subclause 4.5 requires that the length of adjacent lines be within 2 mm of each other and that no line be more
than 2,5 mm from the mean length.
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5.4 Convergence
Convergence shall be evaluated using the grid lines of the test pattern shown in Figure 3 and assessed
visually.
NOTE As stated in 5.3, the grid lines of Figure 3 are 2 pixels in width.
Key
l shortest dimension of display
Figure 3 — Grid pattern for assessment of convergence and geometric accuracy
5.5 White-point and black-point chromaticity and luminance
Luminance and chromaticity measurements should be made with a spectroradiometer meeting the
requirements specified in CIE Publication 122. Tristimulus colorimeters are acceptable and shall be used if no
spectroradiometer is available. However, care should be taken to select a good quality device as discussed in
CIE Publication 122. If the spectroradiometer or tristimulus colorimeter does not meet the accuracy required,
the procedure described in CIE Publication 122 should be used to improve the accuracy for the specific
display type being measured.
The measurements shall be made in the centre of the screen, at the central point shown in Figure 2, and the
sampling rate shall comply with the requirements of CIE Publication 122. The chromaticity of the white should
be obtained by measuring a displayed image consisting of the maximum digital value in each channel (255 for
an 8-bit device) and adjusting the gain of the individual channel amplifiers. Where no such hardware
adjustment is possible, the look-up tables of the driver software shall be altered to accomplish the adjustment.
The black point chromaticity shall be measured in a similar way but at a luminance level of 10 % of the
maximum luminance.
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5.6 Opto-electronic transfer function and tracking
Following setting of the white and black points, the gain, the offset and the gamma shall be determined as
specified in CIE Publication 122. The chromaticity should be measured for at least 10 neutral colours
(R = G = B), at levels of luminance spanning white to full black, and approximately equally spaced in lightness
(L*). From these data, the gain, the offset and the gamma shall be calculated, as specified in
CIE Publication 122. The resultant data will enable confirmation that the values specified in both 4.8 and 4.9
have been achieved.
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Annex A
(informative)
Characterization and calibration
A.1 Matching colour between “hard-copy” and “soft-copy” proofs
Even when the display meets the requirements of this International Standard it does not guarantee that a
displayed (soft-copy) image will match the colour of the same image produced on the hard copy. To achieve a
colour match, it is necessary to provide a colour transformation, such that the colour-data format in which the
image is encoded can be transformed into that required by the colour display and the hard copy system. Thus,
if an image is encoded in a CIE colour space or in some arbitrary RGB or CMYK format, it will be necessary to
transform it to provide a colour match between the proofs. This transformation will normally be achieved by
means of a colour management system [possibly based on the use of ICC profiles which provide the
relationship between the device-specific colour signals (e.g. monitor-drive voltage) and the colour co-ordinates
of the profile connection space (PCS), as defined by the ICC profile specification]. The principles which this
software may well employ for achieving this are discussed below.
For colour CRT displays, the colour mixing required to produce a colorimetric match to any colour may be
defined as a simple linear transformation of the tristimulus values with a correction for gain, offset and gamma,
as discussed in CIE Publication 122. Other non-linear effects, such as cross-talk and internal flare, can usually
be ignored for the quality of CRT displays used for this application. If this is not so, it will be necessary to
modify the transformation calculation, as discussed in CIE Publication 122. It should be noted that without the
correction for gain and offset, the function for gamma will normally be more complex than a simple power-
function correction to take account of the non-linearity required in such a correction, particularly at low
luminance levels. However, when parameters for gain and offset are included, a simple power function usually
provides a reasonably acceptable model.
It should also be noted that the simple model described in the previous paragraph may not be applicable to
colour LCD flat-panel displays. In particular, the gamma-function characteristic familiar to users of CRT
displays may be quite different for LCD displays, in which it may well not be a constant. However, although at
the present time no general recommendations are available for the opto-electronic transfer characteristics of
such displays, they can be included within this International Standard providing that the display drivers are
modified to achieve this specification.
It should also be noted that viewing conditions significantly affe
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