EN ISO 9241-8:1997
(Main)Ergonomic requirements for office work with visual display terminals (VDTs) - Part 8: Requirements for displayed colours (ISO 9241-8:1997)
Ergonomic requirements for office work with visual display terminals (VDTs) - Part 8: Requirements for displayed colours (ISO 9241-8:1997)
Migrated from Progress Sheet (TC Comment) (2000-07-10): Following BT 125/1992, this part of ISO 9241 will undergo a parallel CEN/ISO ++ voting procedure.
Ergonomische Anforderungen für Bürotätigkeiten mit Bildschirmgeräten - Teil 8: Anforderungen an Farbdarstellungen (ISO 9241-8:1997)
Dieser Teil der Norm beschreibt die ergonomischen Mindestanforderungen und Empfehlungen, die für Farben gelten, die Text und Grafikawendungen sowie Bildern diskret zugeordnet werden. Die Spezifikationen in diesem Teil der Norm schließen somit fotorealistische Bilder und Grafiken aus. Diese Norm gilt sowohl für die Anzeigehardware als auch -software, da beide die Erscheinung von Farben auf dem Bildschirm bestimmen.
Exigences ergonomiques pour travail de bureau avec terminaux à écrans de visualisation (TEV) - Partie 8: Exigences relatives aux couleurs affichées (ISO 9241-8:1997)
La CEI 60317-57:2010 spécifie les exigences pour les fils de bobinage de section circulaire en cuivre émaillé de classe 220 avec un revêtement unique à base de résine polyamide-imide, qui peut être modifiée à condition qu'elle conserve l'identité chimique de la résine initiale et réponde à toutes les exigences spécifiées du fil. Une classe 220 est une classe thermique qui exige un indice de température minimal de 220 et une température de choc thermique d'au moins 240 °C.
Cette publication doit être lue conjointement avec la CEI 60317-0-1:2008.
Ergonomic requirements for office work with visual display terminals (VDTs) - Part 8: Requirements for displayed colours (ISO 9241-8:1997)
General Information
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Standards Content (Sample)
SIST EN ISO 9241-8:2001
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SIST EN ISO 9241-8:2001
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SIST EN ISO 9241-8:2001
Is0
INTERNATIONAL
9241-8
STANDARD
First edition
1997-l o-01
Ergonomic requirements for off ice work
with visual display terminals (VDTs) -
Part 8
Requirements for displayed colours
Exigences ergonomiques pour travail de bureau avec terminaux 2 &rans
de visualisation (TEV) -
Partie 8: Exigences relatives aux couleurs atfichbes
Reference number
IS0 9241-8: 1997(E)
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SIST EN ISO 9241-8:2001
IS0 9241=8:1997(E)
Contents
Scope . . . . . . . . . . . . . . . . . . . . . . . .~.*.
Page 1
Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .“.~~.~
Page 1
. . . . . . . . . .*.*.
Definitions
Page 2
Guiding principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.
Page 8
Visual performance objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*.*.
Page 9
Design requirements and recommendations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page 10
Measurement conditions and conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*
Page 13
Compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page 20
Annexes
A Colour difference calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*.
Page 21
B Visual performance test status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Page 25
C Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .~.
Page 26
0 IS0 1997
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 the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet central @ iiso.ch
x.400 c=ch; a=400net; p=iso; o=isocs; s=central
printed in Switzerland
ii
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SIST EN ISO 9241-8:2001
IS0 9241=8:1997(E)
0 IS0
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of national standards’ bodies (IS0
member bodies). The work of preparing International Standards is carried out through IS0 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. IS0 collaborates closely with the International Electrotechnical Commission (IEC)
on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication of an International Standard requires approval by at least 75% of the member bodies casting a vote.
International Standard IS0 9241-8 was prepared by Technical Committee ISO/TC 159, Ergonomics, Sub-
committee SC 4, Ergonomics of human system interaction
IS0 9241 consists of the following parts, under the general title Ergonomic requirements for office work with visual
display terminals (VDTs):
- Part I: General Introduction
- Part 2: Guidance on task requirements
- Part 3: Visual display requirements
- Pan 4: Keyboard requirements
- Part 5: Workstation layout and postural requirements
- Part 6: Environmental requirements
- Part 7: Display requirements with reflections
- Part 8: Requirements for displayed co/ours
- Part 9: Requirements for nonkeyboard input devices
- Part 10: Dialogue principles
- Part 1 I: Guidance on usability
- Part 12: Presentation of information
- Part 13: User guidance
- Part 14: Menu dialogues
- Part 15: Command dialogues
- Part 16: Direct manipulation dialogues
- Part 17: Form-filling dialogues
Annexes A, B and C of this part of IS0 9241 are for information only.
. . .
III
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IS0 9241-8: 1997(E) 0 IS0
Introduction
The purpose of this part of IS0 9241 is to prescribe basic specifications for colours on computer display terminals to
ensure their visibility, identification and discrimination.
The specifications in this part address colour images (visual “stimuli”), their appearance (visual “perception”) and
identification (colour “naming”). The specifications thus address both the perceptual components of colour (such as
detection of saturation and lightness) and some cognitive components (such as naming of specific colours). Other
cognitive components will be addressed in IS0 9241-12.
The ability to detect, identify and discriminate colours on display terminals determines the usefulness of colour in
the perception and interpretation of the computer-generated image. Colour perception of displayed images
depends on a number of factors such as:
hardware and software components of the display system,
physical characteristics of the display image,
the ability of the viewerto perceive the colours,
the lighting in the viewing environment.
The primary characteristics of these factors (that is display, image, viewer and environment) that affect colour
appearance are shown in table 1.
Table 1 - Examples of factors affecting colour appearance
Factor affecting colour appearance
Source
Display Luminance
Spectral distribution and range
Phosphor tvbe
I Screen treatment for reflection control
Resolution
I
Adjacent colours
Image
Size
Spatial frequency content
Viewer State of visual adaptation
Colour-perception ability
I Room I Illumination level I
I Colour temperature of the illumination
Colour interpretation depends on the ability of the viewer to associate a colour with a specific meaning, function, or
action. It is thus important that colours assigned to images on displays be carefully chosen to achieve intended
effects or convey intended meaning. However, the appearance of colours may vary among different suppliers’
displays. For example, the blue on one display may appear darker and more purple than on another, and red may
appear more orange.
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SIST EN ISO 9241-8:2001
o Is0 IS0 9241=8:1997(E)
INTERNATIONAL STANDARD
Ergonomic requirements for office work with visual
display terminals (VDTs) -
Part 8:
Requirements for displayed colours
1 Scope
This part of IS0 9241 describes minimum ergonomic requirements and recommendations to be
applied to colours assigned to text and graphic applications and images in which colours are discretely
assigned. The specifications in this part thus exclude photorealistic images and graphics.
This part of IS0 9241 applies to both hardware and software for visual display terminals, because both
these sources control the presentation and appearance of colour on the display screen.
The specifications, measurements and test procedures described in this part of IS0 9241 are for
displays that produce colour images and are intended to be independent of display technologies unless
otherwise specified.
The specifications in this part of IS0 9241 are for images on computer displays that meet minimum
Displays conforming to this part will be suboptimal
requirements for users with normal colour vision.
for persons with colour vision deficiencies.
This part of IS0 9241 is complementary to IS0 9241-3. The tasks and conditions of use in this part
are similar to those described in IS0 9241-3, unless otherwise specified. This part of IS0 9241 is not
intended to be a specification on colour coding.
Although the primary users of this part of IS0 9241 are intended to be hardware and software user-
interface designers and manufacturers, it will also be useful to those persons responsible for procuring
colour displays and those evaluating the use of colour in the user-interface of the computer system.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions
of this part of IS0 9241. At the time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this part of IS0 9241 are encouraged to
investigate the possibility of applying the most recent editions of the standards listed below. Members
of IEC and IS0 maintain registers of currently valid International Standards.
IS0 9241-3 : 1992 Ergonomic requirements for office tasks with visual display terminals (VDTs) -
Par? 3 : Visual display requirements.
1
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IS0 9241=8:1997(E)
--I) Ergonomic requirements for office tasks with visual display terminals (VDTs) - Par? 5:
IS0 9241-5:
Workpl&e requirements.
3 Definitions
For the purposes of this part of IS0 9241, the following definitions apply.
3.1 achromatic (perceived) colour:
(1) Perceived colour devoid of hue.
The colour names white, gray and black are commonly used or, for transmitting objects, colourless and
neutral.
(2) cpsychophysical sense> See achromatic stimulus 845-03-06. [CIE 17.4 / IEC 50, 845-02-261
3.2 adaptation (visual): Process by which the state of the visual system is modified by previous and
present exposure to stimuli that may have various luminances, spectral distributions and angular
subtenses. [CIE 17.4 / IEC 50, 845-02-071
3.3 additive mixing: Stimulation that combines on the retina the actions of various colour stimuli in
such a manner that they cannot be perceived individually. [CIE 17.4 / IEC 50, 845-03-I 51
3.4 brightness: Attribute of a visual sensation according to which an area appears to emit more or
less light. [CIE 17.4 / IEC 50, 845-02-281
3.5 chroma: Chromaticness, or coloutfulness, of an area judged as a proportion of the brightness of a
similarly illuminated area that appears white or highly transmitting. [CIE 17.4 / IEC 50, 845-02-421
3.6 chromaticity: Property of a colour stimulus defined by its chromaticity coordinates, or by its
dominant or complementary wavelength and purity taken together. [CIE 17.4 / IEC 50, 845-03-341
3.7 chromaticity coordinates: Ratio of each of a set of three tristimulus values relative to their sum.
[CIE 17.4 / IEC 50, 845-03-331
NOTES
1 As the sum of the three chromaticity coordinates equals one, two of them are sufficient to define a chromaticity.
2 In the CIE standard calorimetric systems, the chromaticity coordinates are represented by the symbols x, y, z and xlO, ylO,
and zlO.
3.8 chromaticity diagram: Plane diagram in which points specified by chromaticity coordinates
represent the chromaticities of colour stimuli. [CIE 17.4 / IEC 50, 845-03-351
NOTE -In the CIE standard calorimetric systems, y is normally plotted as ordinate and x as abscissa, to obtain an x, y
chromatici ty diagram (see figure 1 and 3.10).
1) To be published.
2
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SIST EN ISO 9241-8:2001
IS0 9241=8:1997(E)
0 IS0
‘1
006
OS
0,4
a3
02
O,l
I I I I -
I
0
0 0,1 02 0,3 0,4 OS 006
u'
NOTE - The numbers along the curve are the wavelengths of light, in nanometres.
Figure 1 - CIE 1976 uniform-chromaticity-scale diagram;
CIE 1976 UCS diagram
3.9 chromostereopsis: Phenomenon in which two visual objects that differ in dominant wavelength
and/or brightness appear to be at different distances from the viewer.
3.10 CIE 1976 uniform-chromaticity-scale diagram; CIE 1976 UCS diagram: Uniform-chromaticity-
scale diagram produced by plotting in rectangular coordinates V’ against u’, quantities defined by the
equations (1):
4x
4x
u’=
x+15y+32= -2x+lZy+3
(1)
9Y 9Y
VI=
X+l5Y+32 = -2x+l2y+3
I
X, Y, 2 are the tristimulus values in the CIE 1931 or 1964 standard calorimetric systems, and X, y are
the corresponding chromaticity coordinates of the colour stimulus considered. [CIE 17.4 / IEC 50, 845-
03-531.
NOTE - This diagram is a modification of and supersedes, the CIE 1960 UCS diagram in which v was plotted against u in
rectangular coordinates. The relationships between the two pairs of coordinates are:
U' = u:v' = 1,s
3.11 CIE L*u*v* colour space; CIELUV colour space:
Three-dimensional, approximately uniform colour space produced by plotting in rectangular
coordinates L*, u*, V* quantities defined by the equations (2):
1
L*=116(Y/Yn)3 -16; Y/Y,>O,OO8 856
u*=13L*(u’-ul,,
v*=13L*(v’-vl,,
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IS0 9241=8:1997(E)
Y, u', V’ describe the colour stimulus considered and Y,, u’“, v’, describe a specified white achromatic
stimulus. (See CIE 15.2) [CIE 17.4 / IEC 50, 845-03-541
NOTE - Approximate correlates of CIE 1976 u, v lightness, CIE 1976 u, v saturation, CIE 1976 u, v chroma and CIE
1976 u, v hue may be calculated as follows:
C/E1976 lightness L* = 116(Y/Y$ - 16;
Y/v, >0,008856
1
CIE 1976 v, u saturation suv = 13[(u’-U;)* + (v+;)*]T
1
C/E 1976, v, u chroma CL” = u** + v** 2 = L*su,
[ 1
C/E 1976 v,u hue-angle h,, = arctan (v’ - VA) / (u’ - &)I = arctan (v* I u*)
1
3.12 CIE 1976 L*u*v* colour difference: CIELUV colour difference: Difference between two colour
stimuli, defined as the Euclidean distance between the points representing them in the L* U* V* space
and calculated as equation (3): (See CIE 15.2) [CIE 17.4 / IEC 50, 845-03-551
AE;, = [(AL*)* +(Au*)* +(Av*)"]'
(3)
NOTE - The CIE U, v hue-difference may be calculated as follows:
A&) =
[@EL,)* -(AL*)* -(AC;,)*~'
3.13 CIE standard illuminants: llluminants A, B, C, D65 and other illuminants D, defined by the CIE in
terms of relative spectral power distributions. (See CIE 15.2) [CIE 17.4 / IEC 50, 845-03-121
NOTE - These illuminants are intended to represent:
A, Planckian radiator at a temperature of about 2856 K;
B, direct solar radiation (obsolete);
C, average daylight (obsolete);
D65, daylight including the ultraviolet region.
3.14 colour detection: Perception of the presence of a colour on a visually noisy background.
3.15 colour discrimination: Detection of colour difference between visual stimuli.
3.16 colour identification: Perception signified by the ability to name a colour.
3.17 colour interpretation: Association of a particular colour to a meaning or function.
3.18 colour temperature: Temperature of a Planckian radiator whose radiation has the same
chromaticity as that of a given stimulus. It is expressed in kelvins. [CIE 17.4 / IEC 50, 845-03-491
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0 IS0
OJ
I 1, I I I I -
0
0 0,1 02 a3 004 OS 0,Q
u
Figure 2 - Location of CIE illuminant DG5 and colour temperatures on a 1976 CIE UCS diagram
3.19 chromaticity uniformity difference: A distance in the CIE 1976 UCS diagram.
Lwvk& -u;)‘+(v; -v;)
where
IX;, V; and u;, V;
are the coordinates of the same colour displayed at sites 1 and 2.
3.20 complementary wavelength (of a colour stimulus) (h c): Wavelength of the monochromatic
stimulus that, when additively mixed in suitable proportions with the colour stimulus considered,
matches the specified achromatic stimulus. (CIE 17.4 ! IEC 50, 845-03-45)
3.21 convergence: The exact intersection of electron beams of a colour CRT at a specific point on the
plane of its phosphor screen. See figure 3.
Misconvergence is the departure from convergence. See figure 4.
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0 IS0
ConvergedCRT
Electron beams
(R - red;G - green;
B - blue)
GBRG BRG
Screen position
Figure 3 - CRT converged R,G,B electron beams
MisconvergenceCRT
Redbeam
Greenbeam
Blue beam
RGBRGBRGB
Misconvergence
l---H-
Screen position
Figure 4 - CRT misconverged R,G,B electron beams
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SIST EN ISO 9241-8:2001
0 IS0 IS0 9241=8:1997(E)
3.22 default colour set: Predetermined group of colours assigned by the software application or
operating system.
3.23 defective colour vision: Anomaly of vision in which there is a reduced ability to discriminate
some or all colours. [CIE 17.4 / IEC 50, 845-02-131
3.24 depth-of-field: Range of visual focus of images from the distance at which all images are in
focus.
3.25 design viewing distance: Distance, or range of distances, between the screen and the
operator’s eyes for which the display is designed to be viewed (see IS0 9241-3:1992, 2.12).
3.26 dominant wavelength: Wavelength of the monochromatic stimulus that, when additively mixed in
suitable proportions with the specified achromatic stimulus, matches the colour stimulus considered.
NOTE - In the case of purple stimuli, the dominant wavelength is replaced by the complementary wavelength.
[CIE 17.4 /
IEC 50,84503-441
3.27 hue: Attribute of a visual sensation, according to which an area appears to be similar to one of the
perceived colours red, yellow, green or blue, or a combination of two of them. [CIE 17.4 / IEC 50, 845-
02-351
3.28 just-noticeable difference: Perceptual unit which specifies the amount of least physical change
of an image at which the difference can be detected.
3.29 lightness: Brightness of an area judged relative to the brightness of a similarly illuminated area
that appears to be white or highly transmitting. [CIE 17.4 / IEC 50, 845-02-311
3.30 luminance contrast: Ratio between the higher (LH) and lower (LL) lumin,ances that define the
feature to be detected and measured by contrast modulation, cafculated by:
LH - LL
-
c rn=
LH + LL
or contrast ratio (CR), defined as:
LH
-
--
-
CR
LL
[ISO 9241-3:1992, 2.221
3.31 luminance coefficient (at a surface element, in a given direction, under specified
conditions of illumination), g,, 9: Quotient of the luminance of the surface element in the given
direction by the illuminance of the medium. It is expressed in reciprocal steradians (St=-’ ) [IEC 50, 845-
04-711
3.32 calorimetric purity, pc: Quantity defined by the relation
Ld
-
P
c -
CL,+ L(j)
where Ld and Ln are the respective luminances of a monochromatic stimulus and of a specified
achromatic stimulus that match the colour stimulus considered in an additive mixture. [CIE 17.4 / IEC
50,845-03-471
3.33 reference white: Specified white achromatic stimulus Yn, u;t, v’~.
3.34 saturated colour: Colour with a calorimetric purity of one (1).
3.35 saturation: Chromaticness, or colourfulness, of an area judged in proportion to its brightness.
[CIE 17.4 / IEC 50, 845-02-411
3.36 simple graphics: Computer-generated graphs, charts, icons and pictures composed of lines or
area-fill which are not continuous shades, photo-like in appearance or having few gray levels.
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3.37 spectrum locus: Locus in a chromaticity diagram or colour space of the points that represent
monochromatic stimuli throughout the spectrum.
3.38 spectrally extreme colours: Extreme blue (any colour with V’ < 0,2) and extreme red (any colour
with u’ > 0,4).
The extreme regions are illustrated in figure 5.
0
0 a1 0.2 0,3 0,4 OS 0,6
u’
NOTE - Filled-in areas show spectrally extreme colours of a cathode ray tube gamut (indicated by the triangular outline).
Figure 5 - Spectrally extreme colours
3.39 stereopsis: Binocular, visual perception of depth or three-dimensional space.
3.40 trltanopia, small-field: Normal reduction in colour discrimination for short-wavelength (perceived
as blue) images of small angular subtense (approximately 20 minutes of arc or less) stimulating the
central fovea of the eye.
3.41 tristimulus values: Amounts of the three reference stimuli, in a given trichromatic system,
required to match the colour of the stimulus considered. [CIE 17.4 / IEC 50, 845-03-221
3.42 uniform-chromaticity-scale (UCS) diagram: Two-dimensional diagram in which the coordinates
are defined with the intention of making equal distances represent as nearly as possible equal steps of
colour discrimination for colour stimuli of the same luminance throughout the diagram. [CIE 17.4 / IEC
50, 845-03-521
4 Guiding principles
For
Colour can enhance the visual and cognitive processing of information on display screens.
example, colour can help locate, classify, and associate images (i.e. show a relationship between
information).
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The application of colour to display images and their backgrounds should facilitate the correct
perception, recognition and interpretation of images and information. Colour assignment should be
consistent with human factor engineering (ergonomic) guidelines (see annex C) and accepted practice.
The incorrect use of colour can reduce the perception of information displayed on the screen.
NOTES
1 It is not possible for a computer display to produce all the colours that can be perceived by the human visual system (see
figure 6).
0
0,3 084 OS 0,6
u*
A CRT colour production
B Visible colour range
Figure 6 - Colour gamut of a CRT
The triangle superimposed on the 1976 CIE chromaticity diagram shows the limited range of chromaticities generated by a
CRT compared to chromaticity visibly perceptible (cross-hatch).
vision deficiencies is important to computer applications where
2 Providing colours that accommodate viewers with colour
both colour identification and discrimination are critical.
Less than 0,1% of people are unable to perceive hue. However, approximately 8% of males and 0,5% of females are colour-
vision deficient. The most frequently occurring colour deficiency is the inability to distinguish red, yellow and green; other
colours easily confused by colour-vision deficients are cyan from white and blue from purple. Ensuring sufficient brightness
differences between colours eliminates confusion between them. Thus, if a yellow has a high luminance value, a green has a
medium luminance, and a red has a low luminance value, all users should be able to detect differences between them.
5 Visual performance objectives
The primary objective of presenting information in colour on a display screen is to enhance the user’s
ability to process information. This objective is obtained if colours can easily be detected, identified,
and discriminated, and if the assignment of meaning to colour is appropriate to the task. Although
colours can be used for aesthetic purposes, the selection of colours for this purpose should not impede
visual performance and information processing.
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IS0 9241-8: 1997(E)
The physical characteristics of images (such as size) impact the ability to identify and discriminate their
colours. The effect of these physical characteristics on colour perception should be analyzed and
considered when choosing colour for display screen images and their background. Colours and colour
combinations that cause unintended visual effects should not be used.
6 Design requirements and recommendations
The discriminability of pairs of colours depends on differences in both chromaticity and luminance. The
colour difference calculation requirements in this section are based on the colour space as defined by
the CIE in 1976. See clause 3 and annex A for further information on CIE colour space and colour
difference calculations.
6.1 Default colour set
When an application requires the user to discriminate or identify colours, it shall offer a default set of
colours (see 6.9.1 regarding number) which meets the requirements of this part of IS0 9241. If the
colour can be altered by the user, the default set of colours shall be retrievable and restorable.
6.2 Colour uniformity
For an intended uniform colour appearance, the chromaticity differences of a colour at different
locations on the screen shall be as specified in table 2.
Table 2 - Colour uniformitv
Diagonal of the active area in mm
Maximum Au%'
Design viewing distance in mm
< 0,75 0,02
0,03
2 0,75
NOTE - AE* uv has not been used to calculate chromaticity uniformity because it only applies to immediately adjacent
colours. The two categories in table 2 are based on the reduction in colour discrimination as colours are spatially separated.
6.3 Colour misconvergence
The level of misconvergence at any location on multicolour, shadow mask CRT screens shall not be
greater than 3,4 minutes of arc and preferably should be less than 2,3 minutes of arc at the design
viewing distance.
NOTES
1 The convergence of electron beams is a major component in the appearance, quality and resolution of a CRT image.
Convergence is especially important when resolution is critical, such as when reading alphanumeric characters.
2 If the electron beams are not correctly aligned (that is, they are misconverged) on the phosphor triads, they cause the
appearance of colour fringes or double images along the edges of an image. Since these fringes reduce image resolution, they
can reduce user performance.
3 The lower value of misconvergence (that is, 2,3 minutes of arc) is noticeable, but not visually distracting.
4 As the distance between the viewer and the display decreases, the ability of the operator to detect misconvergence
increases. Red-green beam misconvergence is the most perceivable of the beam combinations. For line width of 1 to 2
minutes of arc, as little as 0,5 minutes of arc of red-green beam misconvergence is detectable. Blue-green beam
misconvergence, the least perceivable of the beam combinations, is detectable at slightly over 1,0 minutes of visual arc.
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SIST EN ISO 9241-8:2001
IS0 9241-8: 1997(E)
0 IS0
6.4 Character height and object size
6.4.1 Character strings and data fields
Where accurate colour identification of alphanumeric character strings and data entry fields is required,
the character height shall subtend at least 20 minutes of arc at the design viewing distance.
6.4.2 Isolated images
Where accurate colour identification of an isolated image (e.g. a character or a symbol) is required, the
image should subtend at least 30 minutes of arc at the design viewing distance, and preferably 45
minutes of arc.
6.4.3 Small images
The use of spectrally extreme blue (v’ < 0,2) should be avoided for images subtending less than 2’.
NOTES
1 Multicolour displays produce not only luminance contrasts between the characters and the background, but also produce
colour contrasts that improve total contrast threshold, legibility and readability of text and symbols.
2 Colour images composed of thin lines are often difficult to identify and discriminate, especially on light-emissive displays.
Thus, the colours of individual characters composed of single strokes such as “l”, Y’, and “/” and symbols such as “(” and ‘Y’
are not accurately perceived unless they subtend at least 30 minutes of arc (enough area on the retina to stimulate accurate
colour identification) at the design viewing distance. Colour pairs that are easily confused are those with a small hue angle
difference such as red and orange, blue and purple, and green and cyan. These combinations are especially difficult to
discriminate if they are very bright and of similar brightness, such as white and yellow. White-background emissive displays
further reduce the discriminability of these colour pairs.
6.5 Colour differences
Colour pairs that are to be discriminated shall have values of AE,*, > 20
NOTES
1 If viewers are to accurately discriminate colours, even a AE:,, significantly larger than 20 does not necessarily guarantee
of adjacency and size on colour appearance.
satisfactory perceptual performance because of the effects
2 The lightness difference, AL*, the r
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