Information technology -- Office equipment -- Measurement of image quality attributes for hardcopy output -- Monochrome text and graphic images

ISO/IEC 24790:2017 specifies device-independent image quality attributes, measurement methods and analytical procedures to describe the quality of output images from hardcopy devices. This document is applicable to human-readable monochrome documents produced from printers and copiers. The attributes, methods and procedures rely on measurable properties of printed text and graphic images. Special targets or reference images are not required, but image elements are useful for adequate measurements only if they meet some minimal requirements, e.g. on size or number present. This document is not applicable to images on media other than hardcopy (e.g. images on a visual display) or to images that are intended to be machine readable only (e.g. bar codes).

Technologies de l'information -- Équipement de bureau -- Mesurage des attributs de qualité d'image -- Texte monochrome et images graphiques

General Information

Status
Published
Publication Date
23-Feb-2017
Current Stage
6060 - International Standard published
Start Date
02-Dec-2016
Completion Date
24-Feb-2017
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INTERNATIONAL ISO/IEC
STANDARD 24790
First edition
2017-02
Information technology — Office
equipment — Measurement of image
quality attributes for hardcopy
output — Monochrome text and
graphic images
Technologies de l’information — Équipement de bureau — Mesurage
des attributs de qualité d’image — Texte monochrome et images
graphiques
Reference number
ISO/IEC 24790:2017(E)
ISO/IEC 2017
---------------------- Page: 1 ----------------------
ISO/IEC 24790:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior

written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of

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copyright@iso.org
www.iso.org
ii © ISO/IEC 2017 – All rights reserved
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ISO/IEC 24790:2017(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Report of results and sampling scheme ....................................................................................................................................... 5

4.1 Report of results .................................................................................................................................................................................... 5

4.1.1 Test identification information ............................................................................................................................ 5

4.1.2 Instrument system ......................................................................................................................................................... 5

4.1.3 Conformance ....................................................................................................................................................................... 5

4.1.4 Sampling scheme ............................................................................................................................................................. 5

4.1.5 Results ....................................................................................................................................................................................... 5

4.2 Sampling of pages ................................................................................................................................................................................. 6

4.3 Sampling of images ............................................................................................................................................................................. 6

4.3.1 General...................................................................................................................................................................................... 6

4.3.2 Discretionary sampling .............................................................................................................................................. 6

4.3.3 Random sampling ........................................................................................................................................................... 7

4.3.4 Whole page sampling ................................................................................................................................................... 8

5 Attributes and their measures ............................................................................................................................................................... 8

5.1 Schema of attributes .......................................................................................................................................................................... 8

5.2 Large area graphic image quality attributes ................................................................................................................. 9

5.2.1 General...................................................................................................................................................................................... 9

5.2.2 Large area R and R ..........................................................................................................................................

max min 9

5.2.3 Large area darkness ...................................................................................................................................................... 9

5.2.4 Background darkness ...............................................................................................................................................10

5.2.5 Graininess ...........................................................................................................................................................................11

5.2.6 Mottle ......................................................................................................................................................................................13

5.2.7 Background extraneous mark ...........................................................................................................................14

5.2.8 Large area void ...............................................................................................................................................................15

5.2.9 Banding .................................................................................................................................................................................16

5.3 Character and line image quality attributes ...............................................................................................................17

5.3.1 General...................................................................................................................................................................................17

5.3.2 Character and line image R and R ..................................................................................................

max min 17

5.3.3 Line width ...........................................................................................................................................................................18

5.3.4 Character darkness .....................................................................................................................................................18

5.3.5 Blurriness ............................................................................................................................................................................19

5.3.6 Raggedness ........................................................................................................................................................................20

5.3.7 Character void .................................................................................................................................................................21

5.3.8 Character surround area extraneous mark ............................................................................................22

5.3.9 Character surround area haze ...........................................................................................................................23

6 System conformance ......................................................................................................................................................................................23

6.1 Conformance standard ..................................................................................................................................................................23

6.2 Instrument ...............................................................................................................................................................................................24

6.2.1 OECF conversion ...........................................................................................................................................................24

6.2.2 MTF compensation .....................................................................................................................................................25

6.3 Test objects ..............................................................................................................................................................................................26

6.3.1 Specification for production of lines ............................................................................................................26

6.3.2 Specification for production of large images ........................................................................................31

6.3.3 Slanted edge pattern ........................................................................................................................................... .......34

6.4 Goal values ...............................................................................................................................................................................................34

Annex A (normative) Bitmaps for conformance test lines .........................................................................................................37

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ISO/IEC 24790:2017(E)

Annex B (informative) How to use this document ...............................................................................................................................41

Annex C (normative) Layout of test images for system conformance test ..................................................................54

Annex D (informative) Method to determine R , R and ROI .......................................................................................57

max min

Annex E (informative) Development of system conformance test chart ......................................................................62

Bibliography .............................................................................................................................................................................................................................65

iv © ISO/IEC 2017 – All rights reserved
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ISO/IEC 24790:2017(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are

members of ISO or IEC participate in the development of International Standards through technical

committees established by the respective organization to deal with particular fields of technical

activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international

organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the

work. In the field of information technology, ISO and IEC have established a joint technical committee,

ISO/IEC JTC 1.

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 will 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 on 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 the following

URL: w w w . i s o .org/ iso/ foreword .html.

This document was prepared by ISO/IEC JTC 1, Information technology, Subcommittee SC 28, Office

equipment.

This first edition of ISO/IEC 24790 cancels and replaces ISO/IEC TS 24790:2012 and ISO/IEC 13660:2001,

which have been technically revised.
© ISO/IEC 2017 – All rights reserved v
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ISO/IEC 24790:2017(E)
Introduction

This document is designed to help a quality control engineer evaluate the image quality of prints from

office imaging systems.

In traditional imaging systems (such as ink-on-paper printing), an image is evaluated by comparison to

an original or master version of that image. In many electronic imaging systems, however, the image is

created digitally within the system. There is no hardcopy master and so there can be no evaluation by

comparison in the ordinary way.

Often, those who operate electronic imaging systems ensure good image quality by controlling the

imaging process. They use test targets and reference images to evaluate the performance of the system.

If it is not possible to control image quality by controlling the imaging process and if no test target or

reference image is available, we can rely only on direct evaluation of properties of the image itself.

To perform intrinsic evaluations of image quality, consider the nature of an image that is an output. An

image is some organization of information in space. We assume that these signals have some purpose

or are making some attempt at communication. Good image quality means that the image is legible (the

organization and information can be interpreted) and that it has a pleasing appearance.

Our goals in developing this document were to compile a list of image quality attributes that (taken

together) correlate to human perception of print quality and to develop measurement methods for

these attributes that can be automated and carried out on a simple system.
Legibility and appearance have several aspects:
— detail can be detected easily;
— image elements are well isolated from the background;
— the image has a minimum of gross defects;
— the imaging system has good geometric fidelity.

Not all these factors can be covered by evaluation of intrinsic, quantitative image quality attributes.

Many of them have a large psychological or cultural component that is difficult to evaluate.

A print made with large optical reduction or one that is out of focus can still have excellent edge quality

(and be totally lacking in gross defects, banding, noise, etc.) and yet be illegible. This could occur

primarily because of the high process gamma (contrast) that is characteristic of many xerographic

processes. Thus, the process can produce apparently sharp edges in spite of the loss in resolution.

Without a resolution target of some kind, the extent of the resolution loss, and hence legibility, may not

be known.

The purpose of this document is to present a set of objective, measurable attributes that give some

correlation to the perceived quality of an image to a human observer at a standard viewing distance. This

document allows a user of printed material to sort samples into several groups, from excellent to bad.

The attributes and methods for their assessment are based on several assumptions:

— the image represents an attempt at communication;
— there is uniformity within identifiable image elements;

— character images, symbols and graphic elements are regular (that is, they are intended to be identical

when they have multiple, similar occurrences);
— samples with extreme gross defects have been screened out.
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ISO/IEC 24790:2017(E)

This document applies to monochrome images made up of text, graphics and other image objects with

two tone levels of a single colour (typically black image on white paper) or halftones, images with more

nominal gray levels. This document does not cover continuous tone images, colour images and so on.

Image quality measurement can be thought of as divided into diagnostic (high resolution) and visual

scale (low resolution) procedures. Diagnostic measurements typically use precision test targets and

instrumentation and are key to much engineering work. The present procedure, by contrast, is limited

to phenomena visible to the naked eye and does not permit test patterns.

The working group has taken the approach of selecting simple and (in our judgment) effective metrics,

rather than attempting to prove that our method of doing a given job will always be the most exact.

How will this document actually be implemented? A complete evaluation system has four components:

an image capture device, evaluation software, application-specific quality standards and sampling

plan. The end user may choose to develop all these parts himself or he may choose to purchase one or

more components from a commercial supplier.

Any equipment capable of gathering data appropriate to these measurements is understood to have

a complex instrument function. Rather than attempting to explore the relationship among these

instrument functions, the working group has defined reference images and target values for them. If

these target values are achieved by an instrument, calibration will be acceptably good.

This is not an attempt to break new ground in image science. It is an attempt to provide suppliers and

customers for copies/prints with a practical and objective way to communicate about basic image

quality parameters.

ISO/IEC 13660 was developed and standardized by the point of view described above. ISO/IEC 13660 is

currently the only available systematic image quality attribute measurement standard. ISO/IEC 13660

has had a great influence on related industries and image quality measurement instruments based on

ISO/IEC 13660 are already marketed. However, due to the limited development time, it was standardized

with many issues unresolved and therefore, ISO/IEC 13660 has not been adopted as widely as expected.

The main issues are listed as following:

a) the test chart and methods for measurement system conformance are only specified for some

of character and line attributes. For large area graphic image quality attributes, neither test

charts nor methods are specified. Eight items of image quality attribute for character and line

image and six items of image quality attribute for large area graphic image are defined, and each

measuring method is specified. Of the 14 image quality attributes, the conformance test method,

the conformance test chart and the targeted value for measurement apparatus conformance are

specified for only four of the character and line image quality attributes, leaving 10 of the image

quality attributes with no conformance specifications;

b) physical measures (line width, large area voids) and psychophysical factors (darkness, graininess,

etc.) are intermingled and are all defined as image quality attributes;

c) the goal values for measurement system conformance are available for only four character and line

attributes, and the allowances are very large;

d) when one measures the character and line image quality attributes according to ISO/IEC 13660, the

resulting values have large variation and they do not correspond well with subjective evaluations.

This document added the following content to ISO/IEC 13660 to resolve the issues which ISO/IEC 13660

had and to improve the measurement accuracy.

a) Banding which is a common image quality defect of the hard copy output in a printer or a copying

machine is added as one of the image quality attributes of a large area graphic image.

b) Conformance test charts and the goal values for measurement system qualification are specified

for three character and line image quality attributes and seven large area graphic image quality

attributes.
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ISO/IEC 24790:2017(E)

c) The fundamental resolution of the scanner for measurement was increased from 600 spi to

1 200 spi to reduce the measurement variation.

d) Nearly all of the image quality attributes defined in ISO/IEC 13660 have been redefined in

ISO/IEC 24790 to eliminate intermingling physical measures and psychophysical factors.

e) In order to improve the correspondence between image quality attributes and subjective

evaluations, an image quality attribute measurement evaluation experiment was conducted on

seven items (graininess, mottle, banding, line width, character darkness, blurriness and raggedness)

of image quality attributes to select prediction algorithms for image quality attributes that have

the highest correlation with subjective evaluation. The measurement evaluation experiment was

conducted by five countries which includes Japan, U.S.A, China, South Korea and the Netherlands.

According to the measuring method of the image quality attributes chosen in the measurement

evaluation experiment, the conformance chart was revised and a measurement tool which can measure

automatically all the image quality attributes specified in this document was developed. An initial set

of conformance chart goal values were defined using those tools, and ISO/IEC TS 24790 was published

in 2012.

Experience with the use of the published Technical Specification over the following three years led to

a second revision of the conformance chart, a revision of the conformance evaluation methods and a

revision of the measurement tool. An international conformance chart measurement experiment

was conducted to refine the conformance chart goal values and to establish realistic measurement

tolerances for these goal values. This document is the result of this collective development and

measurement experience.
viii © ISO/IEC 2017 – All rights reserved
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INTERNATIONAL STANDARD ISO/IEC 24790:2017(E)
Information technology — Office equipment —
Measurement of image quality attributes for hardcopy
output — Monochrome text and graphic images
1 Scope

This document specifies device-independent image quality attributes, measurement methods and

analytical procedures to describe the quality of output images from hardcopy devices. This document

is applicable to human-readable monochrome documents produced from printers and copiers.

The attributes, methods and procedures rely on measurable properties of printed text and graphic

images. Special targets or reference images are not required, but image elements are useful for adequate

measurements only if they meet some minimal requirements, e.g. on size or number present. This

document is not applicable to images on media other than hardcopy (e.g. images on a visual display) or

to images that are intended to be machine readable only (e.g. bar codes).
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements 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 2470-1, Paper, board and pulps — Measurement of diffuse blue reflectance factor — Part 1: Indoor

daylight conditions (ISO brightness)

ISO 14524, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic

conversion functions (OECFs)

ISO 21550, Photography — Electronic scanners for photographic images — Dynamic range measurements

ISO 16067-1, Photography — Spatial resolution measurements of electronic scanners for photographic

images — Part 1: Scanners for reflective media
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:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp/
3.1
background area
region outside the edge of any image element (3.16)
3.2
background darkness

appearance of shade in background area (3.1) due to presence of unintended colourant particles that

cannot be resolved as individual marks
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ISO/IEC 24790:2017(E)
3.3
background extraneous mark

colourant particle or agglomeration of colourant particles in the background area (3.1) that is visible at

a viewing distance of 25 cm to 40 cm with the unaided eye
3.4
banding
appearance of one dimensional bands within an area that should be homogeneous
3.5
blurriness

appearance of being hazy or indistinct in outline, a noticeable transition of darkness from line element

to background substrate whose intended transition width is zero (i.e. ideally sharp)

3.6
boundary
contour by reflectance threshold (3.35)
3.7
character darkness
appearance of blackness of a line or character image
3.8
character surround area

region runs from the outer edge of the character image or other image element (3.16) out

500 micrometres
3.9
character surround area haze

colourant particles or agglomerations of colourant particles within a character surround area (3.8) that

are visible, but not resolvable as distinct marks
3.10
character surround area extraneous mark

colourant particle or agglomeration of colourant particles within a character surround area (3.8) that is

visible at a viewing distance of 25 cm to 40 cm with the unaided eye as a distinct mark

3.11
character void

appearance of homogeneity of darkness within the boundary (3.6) of a line segment, character image or

other glyph image
3.12
edge threshold

level in the reflectance gradient profile of an edge that is at 40 % of the transition from the minimum

reflectance factor (R ) (3.33) to the maximum reflectance factor (R ) (3.31) as: R = R + 40 %

min max 40 min
(R – R ).
max min
3.13
graininess

appearance of unintended microscopic, but visible aperiodic fluctuations of lightness

Note 1 to entry: Microscopic means: variations with spatial frequencies greater than about 0,4 cy/mm.

3.14
graphic image
images except a character and a symbol
3.15
image area
region inside portion of inner boundary (3.17)
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ISO/IEC 24790:2017(E)
3.16
image element
single, evidently intentional, object not connected to other objects
3.17
inner boundary

contour of points of an image element (3.16) where edge gradient profiles cross a reflectance level that is

at 10 % of the transition from the minimum reflectance factor (R ) (3.33) to the maximum reflectance

min
factor (R ) (3.31) as: R = R + 10 % (R – R ).
max 10 min max min
3.18
large area darkness
appearance of blackness of a large area graphic image element
3.19
large area

image area (3.15) of graphical element or background that has a minimum size of 12,7 mm in both

dimensions
Note 1 to entry: Equivalent to 600 pixels when sampling resolution is 1 200 spi.
3.20
large area void

visible hole or gap within a solid image area (3.15) that is large enough to be individually distinguished

at a viewing distance of 25 cm to 40 cm
3.21
line image
line at least 1 mm long
3.22
line image density
average optical density (3.27) within the R boundary (3.6)

Note 1 to entry: The average optical density should be converted from average reflectance factor.

3.23
line width

average stroke width, where the stroke width is measured from edge to edge along a line normal to the

center line of the image element (3.16)
3.24
metric
measure of image quality attribute
3.25
monochrome image
image perceived as achromatic colour
3.26
mottle

measure of the appearance of unintended, aperiodic macroscopic fluctuations of lightness

Note 1 to entry: Macroscopic means: variations with spatial frequencies less than about 0,4 cy/mm.

3.27
optical density

negative logarithm to the base 10 of the reflectance factor (3.30), measured using a 0/45-degree

...

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