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

ISO/IEC TS 24790:2012 specifies device-independent image quality attributes, measurement methods, and analytical procedures to describe the quality of output images from hardcopy devices. It 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 must meet some minimal requirements, e.g. on size or number present, in order to be useful for adequate measurements. ISO/IEC TS 24790:2012 is not applicable to images on media other than hardcopy (e.g. images on a VDT) 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 pour copies papier -- Texte monochrome et images graphiques

General Information

Status
Withdrawn
Publication Date
13-Aug-2012
Withdrawal Date
13-Aug-2012
Current Stage
6060 - International Standard published
Start Date
07-Aug-2012
Completion Date
14-Aug-2012
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TECHNICAL ISO/IEC
SPECIFICATION TS
24790
First edition
2012-08-15
Corrected version
2012-12-15
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 pour copies papier — Texte
monochrome et images graphiques
Reference number
ISO/IEC TS 24790:2012(E)
ISO/IEC 2012
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ISO/IEC TS 24790:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2012

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
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Fax + 41 22 749 09 47
E-mail copyright@iso.org
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Published in Switzerland
ii © ISO/IEC 2012 – All rights reserved
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ISO/IEC TS 24790:2012(E)
Contents Page

Foreword ............................................................................................................................................................ iv

Introduction ......................................................................................................................................................... v

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

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

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

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

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

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

5.3  Character and line image attributes .................................................................................................. 16

6  System conformance .......................................................................................................................... 21

6.1  Conformance standard ....................................................................................................................... 22

6.2  Instrument ............................................................................................................................................ 22

6.3  Test objects .......................................................................................................................................... 23

Annex A (normative) Bitmaps for conformance test lines ........................................................................... 31

Annex B (informative) How to use this Technical Specification .................................................................. 35

Annex C (normative) A layout of test images for system conformance test .............................................. 37

Annex D (informative) Method to determine R , R and ROI .................................................................. 38

max min

Annex E (normative) Goal value ...................................................................................................................... 42

Bibliography ...................................................................................................................................................... 44

© ISO/IEC 2012 – All rights reserved iii
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ISO/IEC TS 24790:2012(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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of the joint technical committee is to prepare International Standards. Draft International

Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as

an International Standard requires approval by at least 75 % of the national bodies casting a vote.

In other circumstances, particularly when there is an urgent market requirement for such documents, the joint

technical committee may decide to publish an ISO/IEC Technical Specification (ISO/IEC TS), which

represents an agreement between the members of the joint technical committee and is accepted for

publication if it is approved by 2/3 of the members of the committee casting a vote.

An ISO/IEC TS is reviewed after three years in order to decide whether it will be confirmed for a further three

years, revised to become an International Standard, or withdrawn. If the ISO/IEC TS is confirmed, it is

reviewed again after a further three years, at which time it must either be transformed into an International

Standard or be withdrawn.

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/IEC TS 24790 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 28, Office equipment.

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

been technically revised.

This corrected version of ISO/IEC TS 24790 cancels the above sentence that states that ISO/IEC TS 24790

cancels and replaces ISO/IEC 13660:2001.
iv © ISO/IEC 2012 – All rights reserved
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ISO/IEC TS 24790:2012(E)
Introduction

This Technical Specification 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, we must consider the nature of an image that is 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 Technical Specification were to compile a list of image 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 might 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 Technical Specification 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.

The standard will allow 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.
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ISO/IEC TS 24790:2012(E)

• 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.

This Technical Specification 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 Technical Specification 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 Technical Specification 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.

1. The test chart and methods for measurement system conformance are only specified for some of

character and line attributes. For large area graphic image 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

2. Physical measures (line width, voids) and psychophysical factors (darkness, graininess, etc.) are

intermingled, and are all defined as image quality attributes

3. The goal values for measurement system conformance are available for only four of character and line

attributes. And the allowances are very large.

4. 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.

The Japanese WG4 which took charge of ISO/IEC 13660 within the SC28 committee of Japan pointed out

these issues, and a NWIP to revise the ISO/IEC 13660 was proposed in January, 2006. Five participating

nations were secured at the NWIP vote, and the NWIP was approved. The project to develop ISO/IEC NP

vi © ISO/IEC 2012 – All rights reserved
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ISO/IEC TS 24790:2012(E)

24790 (Information Technology 3 Office Equipment — Measurement of image quality attributes for hardcopy

output — Monochrome text and graphic images) was started in July, 2006.

The ISO/IEC 24790 project added the following content to ISO/IEC 13660 to resolve the issues which

ISO/IEC 13660 had and to improve the measurement accuracy.

1. 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.

2. Conformance test charts and the goal values for measurement system qualification are specified to

three character and line image attributes and seven large area graphic image attributes.

3. The fundamental resolution of the scanner for measurement was increased from 600 spi to 1200 spi

to reduce the measurement variation.

4. 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.

5. In order to improve the correspondence between image quality attributes and subjective evaluations,

an image quality attribute verification experiment was conducted on seven items of image quality

attributes to select prediction algorithms for image quality attributes that have the highest correlation with

subjective evaluation. The verification experiment was conducted by five countries including Japan,

U.S.A, China, South Korea, and the Netherlands.

Verification of the goal values specified in this Technical Specification is under development.

© ISO/IEC 2012 – All rights reserved vii
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TECHNICAL SPECIFICATION ISO/IEC TS 24790:2012(E)
Information technology — Office equipment — Measurement of
image quality attributes for hardcopy output — Monochrome
text and graphic images
1 Scope

This Technical Specification specifies device-independent image quality attributes, measurement methods,

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

Specification 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 must meet some minimal

requirements, e.g. on size or number present, in order to be useful for adequate measurements. The

Technical Specification is not applicable to images on media other than hardcopy (e.g. images on a VDT) or to

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

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO 5-1:2009, Photography and graphic technology — Density measurements — Part 1: Geometry and

functional notation

ISO 5-3:2009, Photography and graphic technology — Density measurements — Part 3: Spectral conditions

ISO 5-4:2009, Photography and graphic technology — Density measurements — Part 4: Geometric conditions

for reflection density

ISO 2470-1:2009, Paper, board and pulps — Measurement of diffuse blue reflectance factor — Part 1: Indoor

daylight conditions (ISO brightness)

ISO 14524:2009, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic

conversion functions (OECFs)

ISO 21550:2004, Photography — Electronic scanners for photographic images — Dynamic range

measurements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
background area
region outside the edge of any image element
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ISO/IEC TS 24790:2012(E)
3.2
background darkness

appearance of shade in background area due to presence of unintended colourant particles that cannot be

resolved as individual marks
3.3
background extraneous mark

colourant particle or agglomeration of colourant particles in the background area that is visible at a viewing

distance of 25cm - 40cm 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 transition width is zero, if the edge is ideally sharp

3.6
boundary
contour by reflectance threshold
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 out 500 micrometres

3.9
character surround area haze

colourant particles or agglomerations of colourant particles within a character surround area 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 that is visible at a

viewing distance of 25cm - 40cm with the unaided eye as a distinct mark
3.11
edge threshold

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

factor (R ) to the maximum reflectance factor (R ) as: R = R + 40% (R – R )
min max 40 min max min
3.12
fill

appearance of homogeneity of darkness within the boundary of a line segment, character image, or other

glyph image
3.13
graininess

appearance of unintended microscopic but visible aperiodic fluctuations of lightness (microscopic means:

variations with spatial frequencies greater than about 0,4 cy/mm)
3.14
graphic image
images except a character and a symbol
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ISO/IEC TS 24790:2012(E)
3.15
image area
region inside portion of inner boundary
3.16
image element
single, evidently intentional, object not connected to other objects
3.17
inner boundary

contour of points of an image element where edge gradient profiles cross a reflectance level that is at 10% of

the transition from the minimum reflectance factor (R ) to the maximum reflectance factor (R ) as: R =

min max 10
R + 10% (R – R )
min max min
3.18
large area darkness
appearance of blackness of a large area graphic image element
3.19
large area

image area of graphical element or background that has a minimum size of 12.7 mm in both dimensions

(equivalent to 600 pixels when sampling resolution is 1200 spi)
3.20
line image
line at least 1 mm long
3.21
line image density
average optical density within the R boundary

NOTE The average optical density should be converted from average reflectance factor

3.22
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
3.23
metric
measure of image quality attribute
3.24
monochrome image
image perceived as achromatic colour
3.25
mottle

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

means: variations with spatial frequencies less than about 0,4 cy/mm)
3.26
optical density

negative logarithm to the base ten of the reflectance factor, measured using a 0/45-degree geometry,

Illuminant A, and ISO visual density calibration as specified in ISO 5-1, 5-3 and 5-4 with an instrument using

no polarization filters
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ISO/IEC TS 24790:2012(E)
3.27
outer boundary

contour of points of an image element where edge gradient profiles cross a reflectance level that is at 70% of

the transition from the minimum reflectance factor (R ) to the maximum reflectance factor (R ) as: R =

min max 70
R + 70% (R – R )
min max min
3.28
raggedness

appearance of geometric distortion of an edge from its ideal position – an ideal edge should be absolutely

straight along the length of the line
NOTE A ragged edge appears rough or wavy rather than smooth or straight.
3.29
reflectance factor

ratio of the reflected flux as measured to the reflected flux under the same geometrical and spectral conditions

for an ideal 100% diffuse reflecting surface
3.30
max

maximum reflectance factor measured by a slit aperture in the background area, typically of the substrate

3.31
region of interest
ROI
area (inside defined boundaries) that the user wants to analyse

NOTE 1 ROI for character and line image attribute includes image element and background area.

NOTE 2 ROI for large area graphic image attribute is within image area.

NOTE 3 The difference between ROI for character and line image and large area graphic image is shown in Annex D.

3.32
min

minimum reflectance factor measured by a slit aperture in the image element, typically of the image

3.33
spots per inch
spi
spots per 25,4 millimetres
3.34
reflectance threshold

level in the reflectance gradient profile of an edge that is at some specified percentage of the transition from

the minimum reflectance factor (R ) to the maximum reflectance factor (R ) as: R = R + p% (R –

min max p min max
R )
min
3.35
void

visible hole or gap within a solid image area that is large enough to be individually distinguished at a viewing

distance of 25cm - 40cm
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ISO/IEC TS 24790:2012(E)
4 Report of results and sampling scheme
4.1 Report of results
4.1.1 Test identification information

The report shall include the date of the measurements, the identity of the test operator, lot identifications, etc.

4.1.2 Instrument system

The report shall include a description of the instrument system used, noting any of the specifications (see

Clause 6) that are emulated or deviated from in any way.
4.1.3 Conformance

Report the results of the conformance tests, Instrument, specs, Instrument OECF, Instrument dynamic range,

Large area attributes:(7) large area darkness, background darkness, graininess, mottle, background

extraneous mark, void, banding, Character and line attributes:(7) line width, character darkness, blurriness,

raggedness, fill, character suround area extraneous mark, character surround area haze. (See Clause 6 and

Annex B.)
4.1.4 Sampling scheme

The report shall include a complete description of the sampling scheme (4.3) used to select the pages and

images.
4.1.5 Results

For each attribute, the report shall include the number of samples per page and the mean, standard deviation,

and range of the results for each page and for the entire lot.
ORIGINATOR XYZ Printing Company
Test Description Results of March 15, 2012 print set
Date of Report April 2, 2012
Test Operator RJC
INSTRUMENTATION XYZ Optical Company, Model XXX
Type 1200 dpi flatbed scanner
Measurement and analysis software ISO 24790 ANALYZER by ABC Inc.
Instrument OECF compensation software Auto OECF by ABC Inc.
Instrument dynamic range measurement Auto DR by ABC Inc.
software
CONFORMANCE TESTS
Density Measurements within the tolerance
Spatial Measurements within the tolerance
Line Attributes Measurements within the tolerance
Graininess & Mottle Measurements within the tolerance
SAMPLING SCHEME Random Sampling
LARGE AREA IMAGE ATTRIBUTES # of samples/page Mean Std
large area darkness
background darkness
graininess
mottle
background extraneous mark
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ISO/IEC TS 24790:2012(E)
void
banding
CHARACTER AND LINE ATTRIBUTES # of samples/page Mean Std
line width
character darkness
...blurriness
raggedness
fill
character surround area extraneous mark
character surround area haze
Figure 1 — Sample report of an evaluation
4.2 Sampling of pages

The pages chosen shall be taken from a homogeneous lot. They shall all (as far as can be determined) be on

the same substrate, produced with the same process, and be of the same age.

The number of pages to be sampled depends on the user’s optimal balance between risk and cost and on the

uniformity of the process that produced the lot.

Any sampling scheme selected shall allow for the presence of pages with defects beyond the scope of this

Technical Specification (such as physical damage to pages) and pages with defects which would be

unacceptable to practically all observers. These pages should be evaluated separately.

4.3 Sampling of images
4.3.1 General

Three sampling schemes and the information required to specify them in the report of results are given below.

Use one of these three schemes. The report shall contain enough specific information that the sampling

scheme can be duplicated exactly.
4.3.2 Discretionary sampling

In discretionary sampling, a human operator intervenes to select features for analysis, based on some

subjective criteria.
4.3.2.1 Procedure
1) For each attribute, establish decision rules for selecting regions.
Example 1 “Select the 10 regions with the highest apparent mottle.”

Example 2 “Find the 3 lightest character images. Find the 3 darkest character images.”

2) Visually inspect the page and select regions that meet the criteria.
3) Evaluate the attribute within each region selected.
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ISO/IEC TS 24790:2012(E)
4.3.2.2 Specification of sampling scheme
If this sampling method is selected, the report shall include:
1) all decision rules used
2) location of each region evaluated, for each attribute.
4.3.3 Random sampling
4.3.3.1 General

In random sampling, features are taken from a portion of the page that has been selected blindly to represent

the whole page.
4.3.3.2 Procedure
1) Cover the page with a grid of uniform rectangular cells.

2) Select a cell at random (using any random or pseudorandom method that ensures that each cell has the

same chance of being selected as any other).

3) If the attribute being evaluated does not apply to the cell, discard it and select a replacement.

4) Evaluate the attribute within the cell.
5) Sample cells until the desired accuracy is obtained.
4.3.3.3 Specification of sampling scheme
If this sampling method is used, the report shall include:
1) dimensions of the grid cells
2) method of placing grid on page
a) location of origin
b) orientation of axes
3) decision rule for deciding if attribute
...

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