ISO/TR 9241-312:2020

TECHNICAL ISO/TR
REPORT 9241-312
First edition
2020-02
Ergonomics of human-system
interaction —
Part 312:
Readability of electrophoretic displays
Ergonomie de l'interaction homme-système —
Partie 312: Lisibilité des écrans électrophorétiques
Reference number
ISO/TR 9241-312:2020(E)
©
ISO 2020

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ISO/TR 9241-312:2020(E)

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ISO/TR 9241-312:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Literature review on readability and legibility for electronic paper displays .2
4.1 General . 2
4.2 Readability for electronic paper displays . 2
4.3 Legibility . 3
5 Overview . 3
6 Readability evaluation for EPD under 14 levels of illumination conditions .4
6.1 General . 4
6.2 Evaluation condition . 4
6.2.1 Equipment . 4
6.2.2 Participants . 4
6.2.3 Illumination condition . 4
6.2.4 Task (Evaluation methods) . 6
6.3 Experimental results . 6
6.4 Discussion . 7
7 Proposing a baseline setup for readability using VAS evaluation .9
7.1 General . 9
7.2 Experimental condition . 9
7.2.1 Equipment . 9
7.2.2 Participants . 9
7.2.3 Illumination condition .10
7.2.4 Task (Evaluation methods) .10
7.3 Experimental results .10
7.4 Discussion .10
8 Verification of the minimum illuminance for readability of an EPD .11
8.1 General .11
8.2 Experimental condition .11
8.2.1 Equipment .11
8.2.2 Participants .11
8.2.3 Illumination condition .11
8.2.4 Task (Evaluation methods) .11
8.3 Experimental results .11
8.4 Discussion .13
9 Contribution of character sizes to the readability of mobile devices .13
9.1 General .13
9.2 Experimental condition .13
9.2.1 Equipment (specimen) .13
9.2.2 Participants .13
9.2.3 Illumination condition .14
9.2.4 Task (Evaluation methods) .14
9.3 Experimental results .14
9.4 Discussion .15
10 Difference in readability of the contrast ratio of mobile devices .15
10.1 General .15
10.2 Experimental condition .16
10.2.1 Equipment .16
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ISO/TR 9241-312:2020(E)

10.2.2 Participants .16
10.2.3 Illumination condition .16
10.2.4 Task (evaluation methods).16
10.3 Experimental results .16
10.4 Discussion .19
11 Effects of long-term reading on visual functions and subjective symptoms .20
11.1 General .20
11.2 Experimental condition .20
11.2.1 Equipment .20
11.2.2 Participants .20
11.2.3 Illumination condition .20
11.2.4 Task (Evaluation methods) .20
11.3 Experimental results .21
11.4 Discussion .22
12 Evaluation of readability for tablet devices by the severity of cataract cloudiness .22
12.1 General .22
12.2 Experimental condition .23
12.2.1 Equipment .23
12.2.2 Participants .23
12.2.3 Illumination condition .23
12.2.4 Evaluation methods . .23
12.3 Experimental results .23
12.4 Discussion .25
13 Summary .25
14 Context of use for electrophoretic displays .26
Annex A (informative) Standardization of electronic displays .31
Bibliography .34
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ISO/TR 9241-312:2020(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
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. Details of
any patent rights identified during the development of the document can be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
A list of all parts in the ISO 9241-300 series can be found on the ISO website.
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ISO/TR 9241-312:2020(E)

Introduction
Electrophoretic technology has led to the development of reflective e-paper displays (EPD) that have
fundamentally different optical characteristics compared to emissive display devices, such as backlit
liquid crystal displays (LCD) or organic light emitting diode displays (OLED). EPD are used in reading
devices, also known as e-readers. See Annex A for more information on the standardization of electronic
displays.
The ISO 9241-300 series provides requirements from the viewpoint of human beings’ visual properties
and are organized by subjects.
Electrophoretic EPD were selected for the experiments reported in this document because of their
widespread use as electronic reading devices.
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TECHNICAL REPORT ISO/TR 9241-312:2020(E)
Ergonomics of human-system interaction —
Part 312:
Readability of electrophoretic displays
1 Scope
This document provides an overview of recent research on readability of electrophoretic displays.
It also provides information for evaluating readability of electrophoretic displays and defining the
context of their use.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
visual analogue scale
psychometric response measurement scale
3.2
legibility
ability for unambiguous identification of single characters or symbols that may be presented in a non-
contextual format
[SOURCE: ISO 9241-302: 2008, 3.3.35]
3.3
readability
characteristics of a text presentation on a display that affect performance when groups of characters
are to be easily discriminated, recognized and interpreted
[SOURCE: ISO 9241-302: 2008, 3.3.38]
3.4
electronic paper display
EPD
electronic display that shows information by diffuse reflection and holds the image with low power
consumption
3.5
electrophoretic display
electronic paper display (3.4) which forms an image by rearranging charged pigment particles using an
applied electric field
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ISO/TR 9241-312:2020(E)

4 Literature review on readability and legibility for electronic paper displays
4.1 General
[1]
A human action of reading is basically analysed by two subjective attributes, that is, readability and
[2]
legibility .
4.2 Readability for electronic paper displays
[3]
In 2006, Alex Henzen, et al. suggested that the EPD would provide a reader with “immersive
[4]
reading” . Another paper reported that the viewing distance for EPD was similar to that of VDTs at
[5]
around 500 mm, but greater than normal paper, at about 360 mm .
[6]
In 2007, An-Hsiang Wang reported on the visual performance for bending/curvature EPD. This
study indicated a future fashion of EPD, but require further exploration with progress of radiometric
measurements. Wang also reported on the reading comprehension of subjects under several ambient
[7]
illuminance conditions for electronic displays .
[8]
In 2009, there was a report on the difference of usability between EPDs and conventional books , but
it was difficult to generalize, considering the results were based on a group of 20 university students.
I-Hsuan Shen, et al. studied the visual performance and visual fatigue from EPD and found that a greater
[9]
illumination than 700 lx was necessary. Wang studied the effects of ambient illuminance on EPD and
concluded the following:
1) under lower illuminance of 50 lx, the conventional LCD with a transmissive mode was the only choice;
[10]
2) under higher illuminance of 500 lx, the EPD can perform as well as the conventional LCD .
[11]
In 2010, Wang studied the visual performance of those subjects who were advancing in age .
In 2011, Der-Song Lee, et al. investigated the effects of light source, ambient illuminance, character size,
[12]
and interline spacing on visual performance and visual fatigue for reader of electronic displays. H.C.
Wu studied the preferable viewing distance and character size for EPD and suggested that age factors
[13]
can be considered for EPD design and VDT guidelines .
In 2012, Wang examined the effects of text/background colour combinations under three levels of
[14]
ambient illuminance on the discriminating performance of young and elderly subjects. This e-paper
became a guide for the designers of colour EPD. Monika Pӧlӧnen, et al. evaluated eyestrain, visually
induced motion sickness, changes in visual functioning, user experience, and the essential optical
parameters of reading equipment for near-to-eye displays such as small size displays (of mobile phones)
[15]
and paper. The results indicated that reading from a hard copy was the most comfortable experience.
[16]
Wang, et al. investigated the effects of bending curvature EPD , but the sample size was too small to
estimate effectively the effects.
Eva Siegenthaler, et al. concluded that the image quality seemed crucial for reading against the
[17]
expectation of differential effects for reading between EPD and LCD. Siegenthaler, et al. also
[18]
analysed the reading behaviour between EPD and tablet LCD with an eye-tracking measurement.
The participants showed no difference in fixation duration, but there were significant differences
in reading speed in the proportion of regressive saccades under special artificial light conditions. C.
[19]
Connell, et al. studied the reading comprehension of subjects using EPD and tablet LCD. The results
indicated that the subjects read printed material faster than EPD and tablet.
In 2013, Po-Chun Chang, et al. investigated the effects of ambient illuminance and light source on the
reading performance of 100 participants as well as visual fatigue as they read three types of reading
[20]
tasks on an EPD and paper text. This paper showed that the reading speed depended on ambient
illuminance. Simone Benedetto, et al. studied the effects of display technology on visual fatigue over
an average period of 10 days. Their evaluation was to measure the blinks per second of each subject
and the visual fatigue scale. The results suggested that reading on tablet LCD triggered higher visual
[21]
fatigue compared to both EPD and paper .
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ISO/TR 9241-312:2020(E)

In 2014, M. Miyao started to investigate readability of EPD compared to LCD and printed paper under
[22] to [30]
various ambient illuminance levels . The advantage of the experiment was to employ more than
100 participants and to analyse the results by elaborate statistical processing.
[31]
In 2015, S. Matsunami investigated the readability of EPD for aging under various illuminance levels .
4.3 Legibility
By definition, legibility is closely related to typeface design. The typeface design went through changes
from type-casting of lead block to outline font of font data on a computer. The outline font is scalable and
enables desktop publishing (DTP) with increasing display resolution. In the past, bitmap font existed
on a low-resolution display but was not scalable. With the beginning of DTP, the idea of page layout
on a computer emerged in the 1980s, although page layout was originally omnipresent in the printing
industry and publishing world from the age of movable type. Page layout has clearly become conscious
of readability, as proved by the large sales of books in the field of printing and publishing business.
In the field of visual information processing, it is commonly believed that there is a unified concept:
shape perception is explained by spatial frequency. Every shape responding to visual stimulus can be
described as a composite function with a various sinusoidal wave by Fourier analysis of its contrast
[32]
function. Elements of the contrast function are contrast sensitivities to various sinusoidal waves .
[33]
There has been a great deal of research in this fields .
5 Overview
This document explains the following 7 evaluations and results related to readability of EPD:
1) readability evaluation for EPD under 14 levels of illumination conditions (Clause 6);
2) proposing a baseline setup for readability using VAS evaluation (Clause 7);
3) verification of the minimum illuminance for readability of an EPD (Clause 8);
4) contribution of character sizes to the readability of mobile devices (Clause 9);
5) difference in readability of the contrast ratio of mobile devices (clause 10);
6) the effects of long-term reading on visual functions and subjective symptoms (Clause 11);
7) evaluation of readability for tablet devices by the severity of cataract cloudiness (Clause 12).
Equipment used in these reports:
1)
— 6-inch ILU-EPD: Kindle® Paperwhite (2012 model);
1)
— 9,7-inch EPD: Kindle® DX;
1)
— 9,7-inch backlit LCD: iPad3® (2012 launched) model: A1416.
1)
Kindle® is used due to its widespread use as an electronic reading device.
1) Kindle and iPad are trademarks of products supplied by Amazon and Apple, respectively. This information
is given for the convenience of users of this document and does not constitute an endorsement by ISO of these
products.
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ISO/TR 9241-312:2020(E)

6 Readability evaluation for EPD under 14 levels of illumination conditions
6.1 General
The readability of EPD with and without integrated lighting unit (ILU) was compared to liquid crystal
display (LCD) with backlight and printed paper to evaluate the contributions of built-in front- or
backlights on the readability under different ambient illuminance levels from 10 lx to 8 000 lx. The
comparison was carried out under a wide range of illuminance levels. Readability was evaluated using
[22]
short English words .
6.2 Evaluation condition
6.2.1 Equipment
a) 6-inch ILU-EPD
b) 9,7-inch EPD
c) 9,7-inch backlit LCD
d) conventional paper as a reference (whiteness 69 % copy paper)
6.2.2 Participants
a) Number: 110
b) Gender: male (56), female (54)
c) Age: from 19 to 86 [mean: 45,7, standard deviation (SD): 17,8]
6.2.3 Illumination condition
Ideally, it would be best to measure the readability under natural surroundings but those are not stable
and they vary through time. Artificial stable lighting circumstances were created for 110 participants
to make several statistical comparisons. For immersive reading, a small compartment was developed to
produce stable illumination conditions. The compartment was set on a desk in a dark room for optical
measuring. Its structure is shown schematically in Figure 1. Its light source was D65 by certified
fluorescent lights (6 500 K). The illumination level was adjusted incrementally based on sophisticated
electronic circuits. Relations between set values and actual measured values of illuminance are shown
in Table 1.
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Dimensions in millimetres
Key
1 lighting system
2 EPD
Figure 1 — Compartment structure
Table 1 — Illuminance value table
Measured value
Set value
lx
10 13,47
20 22,73
50 51,60
100 101,4
150 151,4
200 176,3
300 261,7
500 516,7
750 787,7
1 000 1 042
1 500 1 591
2 000 1 983
5 000 4 670
8 500 8 017
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