SIST-TP CEN ISO/TR 9241-310:2016

Ergonomics of human-system interaction - Part 310: Visibility, aesthetics and ergonomics of pixel defects (ISO/TR 9241-310:2010)

ISO/TR 9241-310:2010 provides a summary of existing knowledge on ergonomics requirements for pixel defects in electronic displays at the time of its publication. It also gives guidance on the specification of pixel defects, visibility thresholds and aesthetic requirements for pixel defects. It does not itself give requirements related to pixel defects, but it is envisaged that its information could be used in the revision of other parts in the ISO 9241 series.

Ergonomie de l'interaction homme-système - Partie 310: Visibilité, esthétique et ergonomie des défauts de pixel (ISO/TR 9241-310:2010)

Ergonomija medsebojnega vpliva človek-sistem - 310. del: Vidljivost, estetika in ergonomija napak svetlobnih točk (ISO/TR 9241-310:2010)

Ta del standarda ISO 9241 navaja povzetek obstoječega znanja o zahtevah ergonomije za napake pikslov
v elektronskih zaslonih v času njegove objave. Podaja tudi navodila o specifikacijah za napake pikslov, prage vidljivosti in estetske zahteve za napake pikslov. Ta del standarda ne navaja zahtev v zvezi z napakami pikslov, temveč je zasnovan tako, da je njegove informacije mogoče uporabiti pri reviziji drugih delov iz družine standardov ISO 9241.

General Information

• Status: Published
• Public Enquiry End Date: 29-Sep-2015
• Publication Date: 21-Dec-2015
• ICS: 13.180 - Ergonomics
• ICS: 35.180 - IT Terminal and other peripheral equipment
• Technical Committee: VSN - Safety of machinery
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 10-Dec-2015
• Due Date: 14-Feb-2016
• Completion Date: 22-Dec-2015
• Ref Project: CEN ISO/TR 9241-310:2015 - Ergonomics of human-system interaction - Part 310: Visibility, aesthetics and ergonomics of pixel defects (ISO/TR 9241-310:2010)

Standards Content (Sample)

SLOVENSKI STANDARD
01-februar-2016
(UJRQRPLMDPHGVHERMQHJDYSOLYDþORYHNVLVWHPGHO9LGOMLYRVWHVWHWLNDLQ
HUJRQRPLMDQDSDNVYHWOREQLKWRþN,6275
Ergonomics of human-system interaction - Part 310: Visibility, aesthetics and ergonomics
of pixel defects (ISO/TR 9241-310:2010)
Ergonomie de l'interaction homme-système - Partie 310: Visibilité, esthétique et
ergonomie des défauts de pixel (ISO/TR 9241-310:2010)
Ta slovenski standard je istoveten z: CEN ISO/TR 9241-310:2015
ICS:
13.180 Ergonomija Ergonomics
35.180 Terminalska in druga IT Terminal and other
periferna oprema IT peripheral equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN ISO/TR 9241-310
TECHNICAL REPORT
RAPPORT TECHNIQUE
December 2015
TECHNISCHER BERICHT
ICS 35.180; 13.180
English Version
Ergonomics of human-system interaction - Part 310:
Visibility, aesthetics and ergonomics of pixel defects
(ISO/TR 9241-310:2010)
Ergonomie de l'interaction homme-système - Partie
310: Visibilité, esthétique et ergonomie des défauts de
pixel (ISO/TR 9241-310:2010)
This Technical Report was approved by CEN on 19 October 2015. It has been drawn up by the Technical Committee CEN/TC 122.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TR 9241-310:2015 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
European foreword
This document (CEN ISO/TR 9241-310:2015) has been prepared by Technical Committee ISO/TC 159
“Ergonomics” in collaboration with Technical Committee CEN/TC 122 “Ergonomics” the secretariat of
which is held by DIN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
Endorsement notice
The text of ISO/TR 9241-310:2010 has been approved by CEN as CEN ISO/TR 9241-310:2015 without
any modification.
TECHNICAL ISO/TR
REPORT 9241-310
First edition
2010-06-15
Ergonomics of human-system
interaction —
Part 310:
Visibility, aesthetics and ergonomics of
pixel defects
Ergonomie de l'interaction homme-système —
Partie 310: Visibilité, esthétique et ergonomie des défauts de pixel

Reference number
ISO/TR 9241-310:2010(E)
©
ISO 2010
ISO/TR 9241-310:2010(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 2010
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 [e-mail]
Web www.iso.org
Published in Switzerland
ii © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
Contents Page
Foreword .iv
Introduction.vi
1 Scope.1
2 Terms and definitions .1
3 Review of research.3
3.1 Detection of spots .3
3.2 Visibility of pixel defects.16
3.3 Aesthetical acceptability of pixel defects .20
3.4 Ergonomics limits related to pixel defect .20
4 Review of standards.23
4.1 ISO 13406-2, Ergonomic requirements for work with visual displays based on flat panels -
Part 2: Ergonomic requirements for flat panel displays .23
4.2 ISO 9241 300-series.26
4.3 International Electrotechnical Commission (IEC).28
4.4 Video Electronics Standards Association (VESA) Flat Panel Display Measurements
(FPDM) .28
5 Review of industry practice.28
5.1 General .28
5.2 Technical specification.29
5.3 Specification for end customers.29
5.4 Outgoing inspection.29
5.5 Incoming inspection.30
6 Illustrations and descriptions of pixel defects.30
Annex A (informative) Overview of the ISO 9241 series .35
Annex B (informative) Pixel defect industry and market status 2005 .36
Annex C (informative) A draft of a model for acceptable pixel level .37
Annex D (informative) Draft recommendations .42
Bibliography.49

ISO/TR 9241-310:2010(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.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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/TR 9241-310 was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
ISO 9241 consists of the following parts, under the general title Ergonomic requirements for office work with
visual display terminals (VDTs):
⎯ Part 1: General introduction
⎯ Part 2: Guidance on task requirements
⎯ Part 4: Keyboard requirements
⎯ Part 5: Workstation layout and postural requirements
⎯ Part 6: Guidance on the work environment
⎯ Part 9: Requirements for non-keyboard input devices
⎯ Part 11: 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
iv © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
ISO 9241 also consists of the following parts, under the general title Ergonomics of human–system interaction:
⎯ Part 20: Accessibility guidelines for information/communication technology (ICT) equipment and services
⎯ Part 100: Introduction to standards related to software ergonomics [Technical Report]
⎯ Part 110: Dialogue principles
⎯ Part 129: Guidance on software individualization
⎯ Part 151: Guidance on World Wide Web user interfaces
⎯ Part 171: Guidance on software accessibility
⎯ Part 210: Human-centred design for interactive systems
⎯ Part 300: Introduction to electronic visual display requirements
⎯ Part 302: Terminology for electronic visual displays
⎯ Part 303: Requirements for electronic visual displays
⎯ Part 304: User performance test methods for electronic visual displays
⎯ Part 305: Optical laboratory test methods for electronic visual displays
⎯ Part 306: Field assessment methods for electronic visual displays
⎯ Part 307: Analysis and compliance test methods for electronic visual displays
⎯ Part 308: Surface-conduction electron-emitter displays (SED) [Technical Report]
⎯ Part 309: Organic light-emitting diode (OLED) displays [Technical Report]
⎯ Part 310: Visibility, aesthetics and ergonomics of pixel defects [Technical Report]
⎯ Part 400: Principles and requirements for physical input devices
⎯ Part 410: Design criteria for physical input devices
⎯ Part 420: Selection of physical input devices
⎯ Part 910: Framework for tactile and haptic interaction
⎯ Part 920: Guidance on tactile and haptic interactions
The following parts are under preparation:
⎯ Part 143: Form-based dialogues
⎯ Part 154: Design guidance for interactive voice response (IVR) applications
Requirements, analysis and compliance test methods for the reduction of photosensitive seizures and
evaluation methods for the design of physical input devices are to form the subject of a future part 411.
ISO/TR 9241-310:2010(E)
Introduction
This part of ISO 9241 summarises information that ISO/TC 159/SC 4/WG 2, Visual display requirements,
collected on pixel defects and their impact on aesthetics and ergonomics during preparation of ISO 13406 and
other parts in the ISO 9241 “300” subseries. It uses terms and definitions from ISO 9241-302 and
[20]
VESA FDPM .
It is based on research and reports that were available at the end of year 2005. The annexes contain
information upon which the Working Group could not reach consensus, as well as some additional information,
collected during the year 2006, that did not undergo the same review and analysis process as the earlier
material.
vi © ISO 2010 – All rights reserved

TECHNICAL REPORT ISO/TR 9241-310:2010(E)

Ergonomics of human-system interaction —
Part 310:
Visibility, aesthetics and ergonomics of pixel defects
IMPORTANT — The electronic file of this document contains colours which are considered to be
useful for the correct understanding of the document. Users should therefore consider printing this
document using a colour printer.
1 Scope
This part of ISO 9241 provides a summary of existing knowledge on ergonomics requirements for pixel
defects in electronic displays at the time of its publication. It also gives guidance on the specification of pixel
defects, visibility thresholds and aesthetic requirements for pixel defects. It does not itself give requirements
related to pixel defects, but it is envisaged that its information could be used in the revision of other parts in
the ISO 9241 series.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
pixel
smallest addressable spatial unit of a display that can show all the colours of the display
NOTE 1 Typical pixel heights for single-user displays range from 0,05 mm to 0,40 mm. Multi-user displays viewed from
a distance use bigger pixel sizes.
NOTE 2 Adapted from ISO 9241-302:2008, definition 3.4.29.
2.2
subpixel
independently addressable unit of a pixel, the smallest addressable unit of a display, used for spatial dithering
to change colour or luminance
2.3
pixel fault
defective pixel or subpixel that is visible under the intended context of use
[ISO 9241-302:2008]
2.4
pixel defect
pixels that operate improperly when addressed with video information
EXAMPLE A pixel addressed to turn black could remain white. If it never changes state, it is said to be a stuck pixel.
If it changes state without the proper addressing signal, it could be intermittent.
[VESA FPDM 303-6]
ISO/TR 9241-310:2010(E)
2.5
stuck on pixel
bright pixel on a black background
NOTE A stuck on pixel can be observed using a black screen.
[VESA FPDM 303-6]
2.6
stuck off pixel
dark pixel on a white screen
NOTE A stuck off pixel can be observed using a white screen.
[VESA FPDM 303-6]
2.7
stuck dim pixel
grey pixel independent of a white or black background
NOTE A stuck dim pixel can be observed using a white and then a black screen.
[VESA FPDM 303-6]
2.8
defective column/row
complete column or row of pixel defects
[VESA FPDM 303-6]
2.9
partial
pixels or subpixels that have defective sub area of defects
EXAMPLE Part of the pixel is stuck on or off but the rest of the pixel works properly.
[VESA FPDM 303-6]
2.10
temporal and intermittent defect
(sub)pixel defect that exhibits temporal variations not related to any steady-state video input
NOTE Temporal defects can be intermittent, exhibit a sudden change of state, or be flickering. They can be observed
using a white and/or a black screen.
[VESA FPDM 303-6]
2.11
defect cluster
more than one defect present in a cluster of pixels of a defined size, e.g. 5 × 5 pixels
[VESA FPDM 303-6]
2.12
fill factor
amount of the area producing useful luminance compared to the amount of the area allocated to the (sub)pixel
[VESA FPDM 303-3]
2 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
2.13
mura
Japanese word meaning blemish that has been adopted in English to provide a name for imperfections of a
display pixel matrix surface that are visible when the display screen is driven to a constant grey level
NOTE Mura defects appear as low contrast, non-uniform brightness regions, typically larger than single pixels. They
are caused by a variety of physical factors. For example, in LCD displays, the causes of mura defects include
non-uniformly distributed liquid crystal material and foreign particles within the liquid crystal. Mura-like blemishes occur in
CRT, FED and other display devices.
[VESA FPDM 303-8]
3 Review of research
3.1 Detection of spots
3.1.1 General
Detection of spots is somewhat different to detection of spatially periodic targets. The vision research on
spatially periodic targets is more extensive than the research on spots. The main factors affecting the visibility
of small spots are spot size, spot duration, interaction of size and duration, the oblique effect, light adaptation,
location in the visual field and spatial uncertainty.
Reading research [25] showed that the human being has three contrast channels suitable for reading;
luminance contrast, Red-Green contrast and Yellow-Blue contrast. In normal reading, the signal from the
contrast channel with the strongest signal is used and the two other channels are ignored. Since reading is
dependent on detection of character features, it can be assumed that the same mechanism is valid for spot
detection.
Effects of defect colour on spot detection can thus be analyzed for the three contrast channels separately and
the spot will be visible if one or more of the three contrast channels produces a signal that exceeds contrast
threshold.
3.1.2 Spot size
3.1.2.1 General
For small spots the visibility threshold decreases as the target area increases (spatial summation). There are
five different types of spatial summation to consider in the study of pixel defects: Piper's Law, Ricco's Law,
S-cones and M- and L-cones.
Spatial summation explains why stuck on defects on a black background are more visible than stuck off
defects on a white background. On a black background the bright spot is summed with its black background
and the contrast between the summed area and its background remains high enough to be visible. On a white
background the black spot and its bright surround are summed and the contrast between the summed area
and its background rapidly becomes less than threshold, when the size of the summed area increases.
ISO/TR 9241-310:2010(E)
Key
X log stimulus diameter in min of visual angle
Y log in ∆L /L
10 0
NOTE Figure from Blackwell (1986) [29].
Figure 1 — Spatial summation as a function of target size and adaptation level
Log-increment (solid lines) and log-decrement (dashed lines) thresholds ∆L /L plotted as a function of log
stimulus diameter for several adaptation levels. Complete summation (Ricco's Law) is given by a slope of -2.
The area of complete summation decreases as mean luminance level increases. The test stimulus was a
variable diameter circle (3,6 min to 121,0 min) presented for 6 s on a 10° background. Adaptation level, L ,
-5 2 2
ranged from 10 to 10 cd/m . Observers were 19 women, 19 to 26 years old with normal vision. Each freely
scanned the background from a distance of 18,2 m, so that viewing was probably parafoveal for the three
lowest adaptation levels. The test spot could appear at one of eight positions projected on the circumferences
of an imaginary 3° radius circle, and a spatial forced-choice detection task was used to estimate threshold.
Threshold was taken to be the point at which the probability of a correct detection was 0,5, corrected for
chance.
4 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
0,5 ms 930 ms
Key
X area of increment in deg
Y threshold in log quanta per second and deg
background luminance (log quanta/s deg ) 7,83
background luminance (log quanta/s deg ) 5,94
background luminance (log quanta/s deg ) 4,96
background luminance (log quanta/s deg ) 3,65
absolute thresholds
Figure 2 — Summation at cone level or Ricco's law is represented by the solid line with a gradient
of −1
Log luminance (quanta/sec.deg is a another method of expressing illuminance, similar to troland) as a
function of area for two different stimulus duration. Spatial Barlow's data from Lamming D., Spatial Frequency
Channels. Chapter 8. In: Cronly-Dillon, J., Vision and Visual Dysfunction, Vol 5. London: Macmillan Press,
1991. [http://webvision.med.utah.edu/]
ISO/TR 9241-310:2010(E)
3.1.2.2 Piper's Law (probability spatial summation)
Piper's law applies to large-sized spots which are close to visibility threshold: It can hold for up to 24° in size in
the peripheral vision. The mechanism behind the summation is probability summation. It has been
mathematically shown that the probability of detection increases with the square root of the number of retinal
ganglion cells involved.
I Ak= (1)
p
where
I is the intensity of the spot;
A is the area of the spot;
k is a constant.
P
When contrast and brightness are high, Piper's law has no impact on pixel visibility analysis.
3.1.2.3 Ricco's Law (neural spatial summation)
Ricco's law describes effects of neural-level spatial summation. If, close to detection threshold a spot is
creating an image on the retina that covers several photoreceptors (cone cells), ganglion cells can be
connected so that they receive stimuli from several photoreceptors and spatially integrate the signal from
several photoreceptors.
In the fovea, the amount of spatial summation is small and neural spatial summation occurs mainly in the
peripheral vision field. In the fovea, spatial neural summation can occur only up to 2' to 3'. In the parafovea,
the summation can be up to 30'. For rod vision in the peripheral visual field, the summation can be up to 2°.
The amount of spatial neural summation is dependent on the intensity of the stimuli.
I×=Ak (2)
R
where
I is the intensity of the spot;
A is the area of the spot;
k is a constant.
R
When contrast and brightness are high Ricco's law has no impact on pixel visibility analysis, which is
demonstrated by the fact that humans can, in good conditions, detect spots subtending as little as 0,5'.
3.1.2.4 Spatial summation in S-cones (PSF and spacing summation)
The S-cone is critical to the blue-yellow contrast signal. It has (for small spots) only a minor contribution to
luminance contrast and no contribution to red-green contrast.
The human resolution to spots with short-wavelength light contrast is determined by the spatial spacing of the
S-cones and the limitations of the optical system of the human eye (light scattering, chromatic aberration etc).
The characteristics of the optical system can be quantified as the PSF (point spread function) of the eye. The
spacing of S-cones in fovea is well aligned to the PSF for short wavelengths. The highest density of S-cones
occurs not in the centre of the visual field, but at an excentrity of 0,35° to 1°. The peak density is slightly
higher than 10 cones/°, which is equivalent to a spacing slightly denser than one cone per 6'. In the central
visual field there is a zone with no S-cones at all. The diameter of this zone subtends about 0,35°.
6 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
If the spot is smaller than the S-cones spacing, then spatial summation will occur within the photoreceptor.
When evaluating if the blue-yellow contrast of a spot exceeds visibility threshold, any spots or features smaller
than this spacing shall thus be spatially summed for an area of subtending approximately 6'.
3.1.2.5 Spatial summation in M- and L-cones (PSF and spacing summation)
The M- and L cones contribute to all three contrast channels. These cones have the highest spatial resolution
in the fovea of all photoreceptors and set the absolute limit for human visual acuity.
The maximum M- and L- cone density is about 120 cones/°, which is equivalent to a spacing of one cone per
0,5’. When evaluating if the luminance contrast or red-green contrast of a spot exceeds visibility threshold any
spots or features smaller than this spacing shall thus be spatially summed for an area of subtending
approximately 0,5'.
3.1.2.6 Ricco's area
Ricco's area is the area (in the spatial frequency domain) where only partial summation occurs. The broader
between full and partial summation, as well as between partial and no summation depends on the wavelength,
luminance and duration of the stimuli. For practical applications, Ricco's' area can thus be considered an
approximative definition that adds uncertainty to any analysis of spot detection. See Figure 2.
The uncertainty of Ricco's area also explains some of the differences between reported research findings.
3.1.2.7 Spatial summation: Summary
When analysing spot visibility, the effect of spatial summation needs to be considered. For fovea vision, the
spatial width of the summation will be at least 0,5’ and at the most 2’ to 3’ for luminance contrast and red-
green contrast and 6’ for blue-yellow contrast.
3.1.3 Spot duration
The highest detectable temporal frequency is slightly above 100 Hz, but for practical applications about 80 Hz.
With lower average luminance, the maximum detectable frequency decreases towards about 40 Hz.
For frequencies higher than 10 Hz Bloch’s law is valid, according to which the luminance times the duration is
constant:
I×=tk (3)
S
where
I is the intensity of the spot;
t is the duration of the spot;
k is a constant.
S
For frequencies less than 10 Hz, the detection threshold is unaffected by the frequency.
3.1.4 Interaction of size and duration
Within Bloch’s law and spatial summation according to Ricco’s law and cone level spatial summation, the
summation effects are additive. At lower spatial and temporal frequencies no simple relationship exists.
ISO/TR 9241-310:2010(E)
3.1.5 The oblique effect
At horizontal and vertical orientations, elongated targets have lower thresholds than round or square targets.
3.1.6 Light adaptation
The literature and popular literature about contrast dynamics state contradictory ratios for maximum contrast
dynamics, e.g. 2,5:100, 1:100 and 1:1000. These are not in conflict with each other but refer to different
reference situations.
For the purpose of this Technical Report, a normal luminance dynamics range of 3 log units in total is
assumed, extending from 1,5 log units below adaptation luminance to 1,5 log units above adaptation
luminance.
Threshold for light spots is dependent on the adaptation luminance. For adaptation luminances less than
0,1 cd/m², the adaptation luminance has no impact on visibility threshold. For adaptation luminances between
0,1 cd/m² and 10 cd/m², there is an increasing dependency on the adaptation luminance. For adaptation
luminances above 10 cd/m², Weber’s law is valid:
∆I
=k (4)
A
/
where
I is the intensity of the spot;
∆I is the intensity difference threshold for detection;
k is a constant.
A
For normal usage situations  k ≈ 100
The size of the area determining the luminance adaptation is not covered in this report. Local luminance
adaptation occurs concurrently and continuously for different areas of the field of view and could partially
explain why a certain spot luminance can be clearly visible against a background, dimly visible in the
neighbourhood of other patterns and not at all visible within the other luminance pattern.
8 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
Key
1 cones
2 rods
X log background luminance in cd/m
Y log threshold luminance in cd/m
Figure 3 — A psychophysical model of detection thresholds over the full range of vision; source: [26]
ISO/TR 9241-310:2010(E)
Key
a rod response showing compression
X stimulus intensity
Y cone response in µ
Figure 4 — Cone responses vs. Stimulus at various background intensities; source: [30]
A second effect of light adaptation is the impact on visual acuity. The visual acuity improves with higher
adaptation luminance up to about 300 cd/m² (for young adults, the level increases with age).
10 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
Key
1 cone
2 rod
X log L, in millilamberts
Y visual acuity
Figure 5 — For recognition tasks, visual acuity is greatly affected by the level of background
luminance
Two branches are evident, the lower belongs to the rod (scotopic) function and the upper to the cone
(photopic) function. Note the asymptote for both indicating the maximum visual acuity (arrows). The cone
branch has a long "linear" range of about 3 log units which asymptote at the photopic level of about 300 cd/m².
The shallow curve at low luminances is due to the rod response and the large sigmoidal curve is due to the
cone response. The horizontal arrow identifies the maximum resolution of rod and cone systems. Konig's data
from Riggs L. A., Visual acuity. Chapter 11. In: Graham, C. H. (ed), Vision and Visual Perception. New York:
John Wiley and Sons, Inc., 1965. [http://webvision.med.utah.edu/]
ISO/TR 9241-310:2010(E)
Key
X log luminance, in cd/m
Y highest resolvable spatial frequency, in cycles/deg
Figure 6 — Shaler, S. (1937) The relation between visual acuity and illumination; source: [31]
12 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
Note that positive contrast represents a bright spot on a dark background.
Key
Blackwell 1946 (1) Part I positive contrast t = 6 s
Blackwell 1946 (1) Part II negative contrast t = 6 s
Blackwell 1946 (1) Part III positive contrast t = unlimited
Blackwell 1946 (2) positive contrast t = 0,2 s
Figure 7 —The relation between threshold contrast and background luminance (adaptation
luminance); Blackwell (1946, 1971) from http://arrow.win.ecn.uiowa.edu/
ISO/TR 9241-310:2010(E)
Key
X visual angle of target in minutes
Y threshold contrast, in
Lb in cd/m · 2 = 3426,2591
Lb in cd/m · 2 = 34,262591
Lb in cd/m · 2 = 0,34262891
Lb in cd/m · 2 = 0,003426259
2 -5
Lb in cd/m · 2 = 3,42626 · 10
Figure 8 —The relation between threshold contrast, background luminance and visual angle of target,
Exposure time unlimited; Blackwell (1946), part III. from http://arrow.win.ecn.uiowa.edu/
3.1.7 Contrast adaptation
Contrast adaptation is a not so well-known effect which might impact spot detection. It could partially explain
why pixel defects are easier to detect when contrast of the pixel defect is not too far from the average contrast
of the visual field. The visual system appears to have a fairly limited contrast response function and an ability
to compensate by adjusting the gain so that it is optimal for detecting differences in contrast around the
average level of contrast.
th
This contradicts the popular extrapolation of Weber’s law. Although luminance differences as small as 1/100
of the adaptation luminance can be perceived, human beings do not have that resolution available in the
whole luminance range at the same time, but only in a small window, around the adaptation contrast.
14 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
Note that the low contrast response function on the left is ideally suited to detect differences in contrast
between 2 % and about 25 %. But for contrasts above 25 % the neuron can only respond at its maximum level.
Key
X contrast in %
Y response
Figure 9 — Example contrast response functions with low (left curve) and high (right curve) contrast
adaptation levels; source: [27]
3.1.8 Spatial uncertainty
For spots that are close to detection threshold, the detection threshold decreases if the user knows the spatial
location of the spot. (Uncertainty about the intensity or contrast does not decrease detection threshold.)
3.1.9 Spot colour
In some reports a dependency on spot colour has been reported. This dependency can more or less be
attributed to the differences in luminance or luminance contrast.
Gordon Legge et al [28] showed that the human being has three contrast channels suitable for reading;
luminance contrast, Red-Green contrast and Yellow-Blue contrast. In normal reading, the signal from the
contrast channel with the strongest signal is used and the two other channels are ignored. Since reading is
dependent on detection of character features, it can be assumed that the same mechanism is valid for spot
detection.
Adapting Legge et al, the following can be assumed: Spot detection origins from the perceived contrast.
Contrast is perceived through three channels: achromatic (luminance), Red-Green and Blue-Yellow. In spot
detection, the detection is based on the channel with the highest contrast and the channels which have less
contrast do not impact the detection speed. Furthermore, the spatial resolution of the blue-yellow contrast
channel is not as good as the luminance channel, and will not be as efficient in detecting pixel defects
appearing as small spots.
Summarizing, for practical application, it can safely be assumed that the colour will influence pixel defect
detection only through the luminance contrast created by the colours.
ISO/TR 9241-310:2010(E)
3.1.10 Conclusions
Spot detection depends on several factors described above. For the context of electronic visual displays
(currently available technology) the following factors seem to be the most important:
⎯ size of the spot;
⎯ contrast of the spot;
⎯ adaptation luminance.
Differences between positive polarity and negative polarity pixel defects are fully explained by the difference in
light adaptation level and contrast (see Figure 1).
Thus there seems to be no need to define different requirements for positive and negative polarity, if the
requirements are defined as a function of both contrast and adaptation luminance.
3.2 Visibility of pixel defects
Yoshitake [9] reported a study on the spatial summation related to pixel defect visibility threshold. He verified
the hypothesis that for stuck on pixel defects on a black background the luminance times the area is constant.
This is the effect occurring from both Ricco's law and from photoreceptor-level spatial summation. He also
identified several factors that influence the experimental conditions; i.e. factors that need to be included in a
model for pixel defect visibility threshold:
a) display factors:
⎯ colours (wavelength);
⎯ viewing angle characteristics;
⎯ background luminance;
⎯ reflectance;
⎯ fill factor.
b) test subject factors:
⎯ visual characteristics such as visual acuity.
c) environment factors:
⎯ screen illuminance;
⎯ viewing distance;
⎯ viewing angle.
Strik [10] reported a study on the perception of subpixel defects in displays. The display was a typical
advanced mobile phone display. This means a smaller display size and a smaller pixel size compared to
earlier studies. Also the impact of ambient reflections on the display is different from fixed-position larger
displays.
NOTE 1 At the time, high-end mobile displays had a pixel size of 0,15 mm to 0,30 mm. The report should not be
interpreted outside of that context.
16 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
Strik and his colleagues draw the following conclusions, which are valid only for the display characteristics that
the test display had:
a) experts have a significantly lower pixel defect detection threshold than non-experts;
b) defects covering two or more neighbouring pixels will always be noticed by users. (The stroke width of the
test display was one pixel);
c) green subpixels will be noticed by end users;
d) stuck-off blue subpixels are not visible for most viewers;
e) red subpixels are almost invisible for non-experts;
f) a better controlled study is needed to find a numeric acceptance threshold. At least luminance, pixel size
and ambient illumination need to be controlled.
Swinkels et al [11] conducted a well-controlled visual perception study, as a continuation of the research
reported by Strik, with the aim of establishing a numeric visual detection threshold. The results they obtained
were compared with existing models of vision and they were able to establish a numeric model for bright pixel
defect detection on black background, based on numeric addition of the effects from spatial summation,
adaptation luminance and Weber’s law.
−7
10 L
bk
L=+LL+⋅ (5)
th bk bk
tan α 100
where
L is the threshold luminance for pixel defect detection;
th
L is the luminance of the background of the pixel defect;
bk
α is a the visual angle subtended by the pixel defect, in degrees.
NOTE 2 In the experimental condition the adaptation luminance was equal to the background luminance. In real-life
situations the adaptation luminance is the local average luminance around and including the pixel defect. Thus the third
term in the equation should probably be L .
adaptation
The model has the following known limitations:
⎯ The model has been validated with data from only one experiment and that experiment was carried out
only with bright pixels on a black background.
⎯ The model is valid for healthy, young adults with normal vision. For older people and for people with
visual disorders the threshold luminance will be higher.
⎯ The model predicts only the worst case pixel defect visibility, i.e. a single pixel defect in a known location
on a spatially uniform background. In real-world situations the background is usually spatially non-uniform
and there are usually ambient reflections on the screen and some amount of glare in the visual field of the
user. All of which increase the threshold for pixel defect detection.
⎯ The model does not include the change in visual acuity as a function of adaptation luminance.
The data by Swinkels et al has been correlated both to the model proposed by Swinkels et al and to the
contrast thresholds predicted by the simplified contrast sensitivity function by Barten [7], see 3.1.1. The plot
and the correlation indicate that both models predict pixel defect detectability equally well.
ISO/TR 9241-310:2010(E)
Pearson's r correlation coefficient is 0,996 for both equations. The contrast is defined as the luminance
difference (spot – background) divided by the background (adaptation) luminance.
Key
Swinkel's data
Swinkel's equation
Barten's equation
Figure 10 — The correlation of the Swinkels and Barten equations to the Swinkels et al empirical data
It is expected that the Barten model can be more widely applied to different pixel defect cases, such as
stuckoff pixel defects. No explicit validation has however been made. The larger number of parameters in the
Barten model allows for larger adaptability but increases the risk of error from applying the wrong parameters.
[Mustonen & Lindfors 2005] [12] asked their test persons to rate pixel defects on a 9-point scale. For the
display used, all types of pixel and subpixel defects were visible in negative polarity, whereas in positive
polarity stuck off low contrast subpixel defects were very close to imperceptible; and all types of pixel defects
were close to imperceptible at the lowest tested amount of pixel defects (covering 0,02 % or less of the total
display area).
18 © ISO 2010 – All rights reserved

ISO/TR 9241-310:2010(E)
Positive polarity Negative polarity
Rating results are plotted as a function of the display area (%) that the defects cover. Visibility of pixel defects
was assessed with 9 point scale labelled as follows: 1 = very annoying, 3 = annoying, 5 = slightly annoying,
7 = perceptible, but not annoying, 9 = imperceptible. Each data point represents the average over five test
subjects and error bars are standard errors of the mean. Logarithmic trendlines are added.
Key
X percent of display area that the faults cover
Y visibility of pixel defects
reference
stuck off low contrast subpixel
stuck off high contrast subpixel
stuck off pixel
stuck off pixel (2 × 2)
Figure 11 — Subjective evaluation of stuck off defects on white background and stuck on defects on
black background
For techniques used in medical displays to make visible pixel defects
...