ISO/IEC 13660:2001
(Main)Information technology — Office equipment — Measurement of image quality attributes for hardcopy output — Binary monochrome text and graphic images
Information technology — Office equipment — Measurement of image quality attributes for hardcopy output — Binary monochrome text and graphic images
Technologies de l'information — Équipement de bureau — Mesurage des attributs de qualité d'image pour copies papier — Texte monochrome binaire et images graphiques
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Standards Content (Sample)
INTERNATIONAL ISO/IEC
STANDARD 13660
First edition
2001-09-01
Information technology — Office
equipment — Measurement of image
quality attributes for hardcopy output —
Binary monochrome text and graphic
images
Technologies de l'information — Équipement de bureau — Mesurage des
attributs de qualité d'image pour copies papier — Texte monochrome
binaire et images graphiques
Reference number
ISO/IEC 13660:2001(E)
©
ISO/IEC 2001
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ISO/IEC 13660:2001(E)
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ISO/IEC 13660:2001(E)
Contents Page
Foreword.v
Introduction.vi
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Report of results and sampling scheme .4
4.1 Report of results .4
4.1.1 Test identification information .4
4.1.2 Instrument system.4
4.1.3 Compliance.4
4.1.4 Sampling scheme .4
4.1.5 Results .4
4.2 Sampling of pages.5
4.3 Sampling of images.6
4.3.1 Discretionary sampling .6
4.3.2 Random sampling.6
4.3.3 Whole page sampling.7
5 Attributes and their measures.8
5.1 Schema of attributes .8
5.2 Large area density attributes.8
5.2.1 Darkness, large area.8
5.2.2 Background haze.9
5.2.3 Graininess .10
5.2.4 Mottle .11
5.2.5 Extraneous marks, background.11
5.2.6 Voids .12
5.3 Character and line attributes.12
5.3.1 Blurriness .13
5.3.2 Raggedness.13
5.3.3 Line width .14
5.3.4 Darkness, character .14
5.3.5 Contrast .15
5.3.6 Fill.15
5.3.7 Extraneous marks, character field.16
5.3.8 Background haze, character field .17
6 System compliance .18
6.1 Compliance standard .18
6.2 Instrument .18
6.3 Test objects.18
6.3.1 Specification for production of lines .18
6.4 Goal Values .19
Annex A (normative) Bitmaps for compliance test lines .20
Annex B (normative) Hardware compliance test .24
B.1 Density measurements .24
B.1.1 Compliance standard .24
B.1.2 Test objects.24
B.2 Spatial measurements.24
B.2.1 Compliance standard .24
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ISO/IEC 13660:2001(E)
B.2.2 Test objects .24
Annex C (informative) How to use this International Standard .25
C.1 Conditions .25
C.2 Procedure .25
C.3 Sample programs.27
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ISO/IEC 13660:2001(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
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.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
International Standard ISO/IEC 13660 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information
technology, Subcommittee SC 28, Office equipment.
Annexes A and B form a normative part of this International Standard. Annex C is for information only.
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ISO/IEC 13660:2001(E)
Introduction
This International Standard is designed to help a quality control engineer evaluate the 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 International Standard 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 International Standard 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 13660:2001(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 International Standard applies to images made up of text, graphics, and other image objects with two-tone
levels of a single colour (typically black image on white paper). This International Standard does not cover
halftones or images with more nominal gray levels, 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 International Standard actually be implemented? A complete evaluation system has three
components: an image capture device, evaluation software, and 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.
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INTERNATIONAL STANDARD ISO/IEC 13660:2001(E)
Information technology — Office equipment — Measurement of
image quality attributes for hardcopy output — Binary
monochrome text and graphic images
1 Scope
This International Standard specifies device-independent image quality attributes, measurement methods, and
analytical procedures to describe the quality of output images from hardcopy devices. This International Standard
is applicable to human-readable documents composed of binary monochrome images produced from impact
printers, non-impact printers, and copiers.
The attributes, methods, and procedures rely on intrinsic properties of the image. Targets or reference images are
not required. The International Standard 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).
This International Standard is not intended to apply to pictorial art. It is optimized for black colourant forming the
image on a white substrate; it is not intended to be used for dropped out or reversed type or for transparencies.
The evaluation of an image with any other colour of colourant or substrate will be sensitive to changes in
illumination. In this case, the procedures of this International Standard may not be applicable and should be used
with caution.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 5-1:1984, Photography — Density measurements — Part 1: Terms, symbols and notations
ISO 5-3:1995, Photography — Density measurements — Part 3: Spectral conditions
ISO 5-4:1995, Photography — Density measurements — Part 4: Geometric conditions for reflection density
CIE 15.2:1986, Colorimetry
TAPPI T480 om-92, Specular gloss of paper and paperboard at 75 degrees
TAPPI T452 om-92, Brightness of pulp, paper, and paperboard (directional reflectance at 457 nm)
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ISO/IEC 13660:2001(E)
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply. The image quality
attributes themselves are defined in Clause 5.
binary— any system based on exactly two possible values, such as 0/1 or black/white.
binary image— an image with only two fundamental tones: the substrate and the colourant.
boundary— the region of an edge within which the reflectance factor makes the transition from 10% to 90% of the
difference between image and substrate reflectance factors. See also threshold contour.
character image— a specific physical representation of a character glyph.
colourant— the material used to make an image visible. In copying and electronic printing, the two main
colourants are dye and pigment.
density, optical— log10 (1/R), where R is the reflectance factor, measured according with 0/45-degree geometry,
Illuminant A, and ISO visual density calibration.
distortion— undesired change in the shape of an image.
edge threshold— the points in the gradients of an edge that define the location of the edge. This is the threshold
contour corresponding to R for the ROI. See also threshold contour.
60
gradient, edge— the relative reflectance value gradient along a line normal to the edge of an image segment.
hardcopy— a document on a substrate.
human-readable— designed to be interpreted by a standard human viewer.
image element— a single, evidently intentional, object not connected to other objects.
image segment— a collection of image elements that are treated as a unit.
inner boundary edge— the point in the gradient of an edge that is at 90% of the transition from the substrate
reflectance factor to the image reflectance factor: R = R –90%(R – R ).
90 max max min
line width— width of the line measured normal to the line from edge threshold to edge threshold.
monochrome image— an image in one colour or shades of one hue.
nominal— a value used as a reference value. This value is obtained by assumption, by calculation, or by some
other means and then treated as the actual, intended value.
normal edge profile— the reflectance factor gradient along a line normal to the edge of an image segment.
outer boundary edge— the point in the gradient of an edge that is at 10% of the transition from the substrate
reflectance factor to the image reflectance factor: R = R –10%(R – R ).
10 max max min
page— a collection of text, graphics, and other image objects intended to be printed on one side of a sheet of
hardcopy.
pixel— a contraction of the term “picture element”; the smallest geometric unit of information in a digital
representation of an image.
pseudorandom— a sequence which is generated by a predictable process, but which has all the measurable
properties of a truly random sequence that are required for a particular application.
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ISO/IEC 13660:2001(E)
random— a sequence that is generated by a process in which each element is unrelated to the preceding element,
which has no pattern, and which is completely unpredictable.
reflectance factor— the ratio of radiant flux reflected from the sample to the radiant flux incident on the sample.
relative reflectance value— percentage of the transition from the substrate reflectance factor to the image
reflectance factor at a particular point in the image.
region of interest (ROI)— area (inside defined boundaries) that the user wants to analyse.
R — maximum reflectance factor in the ROI, typically of the substrate. This is taken to be the centre of the higher
max
peak in the bimodal reflectance distribution across the ROI.
R — minimum reflectance factor in the ROI, typically of the colourant. This is taken to be the centre of the lower
min
peak in the bimodal reflectance distribution across the ROI.
ROI— see region of interest.
sharpness, edge— the inverse of blurriness. (See 5.3.1.)
spi (spots or samples per inch)— spots or samples per 25,4 millimetres.
standard viewing distance— 300 millimetres, assuming standard visual acuity.
substrate— the material on which a hardcopy document is produced, usually paper.
threshold contour— the points in the gradients of an edge that are at some specified percentage of the transition
from the substrate reflectance factor to the image reflectance factor: R = R –p%(R – R ).
p max max min
tile— a plane figure used for a tiling.
tiling, regular— to cover the plane (or region of the plane) with identical plane figures so that there are no gaps
and there is no overlap of the figures.
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ISO/IEC 13660:2001(E)
4 Report of results and sampling scheme
This clause contains the three possible image sampling schemes (4.3) and a description of the report of an
evaluation carried out under this International Standard (4.1).
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 areemulatedor deviatedfrom inanyway.
4.1.3 Compliance
Report the results of the compliance tests. (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.
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ISO/IEC 13660:2001(E)
ORIGINATOR XYZ Printing Company
Test Description Results of Oct. 17, 1996 print set
Date of Report December 6, 1996
Test Operator RJC
INSTRUMENTATION
XYZ Optical Company, Model XXX
Type
600 spi flatbed scanner
Measurement and analysis software
IMAGE ANALYZER by ABC Inc.
COMPLIANCE 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 DENSITY ATTRIBUTES # of samples/page Mean STD
darkness, large area
background haze
graininess
mottle
extraneous marks, background
void
CHARACTER AND LINE ATTRIBUTES # of samples/page Mean STD
blurriness
raggedness
line width
darkness, character
contrast
fill
extraneous marks, character field
background haze, character field
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
International Standard (such as physical damage to pages) and pages with defects which would be unacceptable
to practically all observers. These pages should be evaluated separately.
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ISO/IEC 13660:2001(E)
4.3 Sampling of images
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 must contain enough specific information that the sampling scheme can be
duplicated exactly.
4.3.1 Discretionary sampling
In discretionary sampling, a human operator intervenes to select features for analysis, based on some subjective
criteria.
4.3.1.1 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.
4.3.1.2 Specification of sampling scheme
If this sampling method is selected, the report must specify:
1 all decision rules used
2 location of each region evaluated, for each attribute.
4.3.2 Random sampling
In random sampling, features are taken from a portion of the page that has been selected blindly to represent the
whole page.
4.3.2.1 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.
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ISO/IEC 13660:2001(E)
4.3.2.2 Specification of sampling scheme
If this sampling method is used, the report must specify:
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 is applicable to cell
4 any other decision rules used
5 decision rule for deciding when to stop sampling
6 method of randomization in selection of grid cells
7 stratification, if any. (Stratification is dividing the grid into homogeneous sections and then selectin
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