ISO 6328:2000
(Main)Photography — Photographic materials — Determination of ISO resolving power
Photography — Photographic materials — Determination of ISO resolving power
This International Standard specifies a method for determining the resolving power of photographic films, plates and papers, including black-and-white films, black-and-white printing papers, colour-reversal films, colour-negative films, and colour-printing papers. Materials designed for X-ray and other high-energy radiation are excluded, as are photographic materials used in medical radiography where the exposure source is an intensifying screen in contact with the film (sensitized on one or two sides). Also excluded are materials having photo-polymer, diazo, etc. light-sensitive layers.
Photographie — Surfaces sensibles — Détermination du pouvoir résolvant ISO
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INTERNATIONAL ISO
STANDARD 6328
Second edition
2000-05-01
Corrected and reprinted
2000-09-01
Photography — Photographic materials —
Determination of ISO resolving power
Photographie — Surfaces sensibles — Détermination du pouvoir résolvant
ISO
Reference number
ISO 6328:2000(E)
©
ISO 2000
---------------------- Page: 1 ----------------------
ISO 6328:2000(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not
be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this
file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this
area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters
were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event
that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2000
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body
in the country of the requester.
ISO copyright office
Case postale 56 � CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.ch
Web www.iso.ch
Printed in Switzerland
ii © ISO 2000 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 6328:2000(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Sampling and storage .3
5 Test method.3
6 Product classification .13
7 Product marking and labelling .14
Annex A (informative) Illustration of an example of a resolving-power camera .15
© ISO 2000 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 6328:2000(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 6328 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 6328:1982), which has been technically revised.
In this revision, the description of the process of evaluating images has been expanded. The specifications of the
resolving power camera’s objectives have been altered slightly, and the illustration of a resolving-power camera
has been moved to informative annex A. The text describing qualification of the camera has been expanded to
include the target.
This second edition also contains many other changes, most of which were made for the sake of clarity of
understanding. Among these changes is a clarification of part of the scope. The definitions have also been
expanded; some terms have been substituted for others in order for their usage to be more consistent and their
meaning to be clearer. The term “element” has been introduced in place of “test pattern” and “tribar resolving-
power target” replaces “test chart”. Other terms introduced or clearly defined include “target polarity”, “limiting
element” and “ISO resolving power”.
Annex A of this International Standard is for information only.
iv © ISO 2000 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 6328:2000(E)
Introduction
The resolving power of a photographic material is used to estimate the smallest detail that may be visually
observable when recorded on the material. It combines the effects of modulation transfer function, graininess and
contrast, all of which contribute to overall image quality, and human observers, each of whom may differ in their
assessment of quality. The method is particularly useful for appraising materials that will be viewed at high
magnification such as microfilm, 8 mm and 16 mm motion picture film, etc. However, resolving power should not
be expected to predict overall image quality in every situation, because image quality is too complex to be
described by a single factor. This is particularly the case for low-contrast continuous-tone products.
Resolving power as measured by photographing suitable tribar resolving-power targets is very dependent on
conditions of measurement, and the structure of the target element. It depends markedly on the photographic
conditions employed and on the presence of background glare from the illuminated target. It is affected by such
factors as the spectral content of the light used, the exposure level, the focus, processing procedures, the lens
aperture at which the test is made, the contrast of the target and the magnification of the camera lens and the
microscope through which the images are observed, etc.
The judgment exercised by the human observer in determining resolving power can be a source of significant
experimental error. The criterion of resolution given in this International Standard was selected because it
appeared to admit less latitude in interpretation than others. The description of the process of evaluating images
has been expanded in this revision.
© ISO 2000 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 6328:2000(E)
Photography — Photographic materials — Determination of ISO
resolving power
1 Scope
This International Standard specifies a method for determining the resolving power of photographic films, plates
and papers, including black-and-white films, black-and-white printing papers, colour-reversal films, colour-negative
films, and colour-printing papers.
Materials designed for X-ray and other high-energy radiation are excluded, as are photographic materials used in
medical radiography where the exposure source is an intensifying screen in contact with the film (sensitized on one
or two sides). Also excluded are materials having photo-polymer, diazo, etc. light-sensitive layers.
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 497:1973, Guide to the choice of series of preferred numbers and of series containing more rounded values of
preferred numbers.
ISO 554:1976, Standard atmospheres for conditioning and/or testing — Specifications.
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
element
three parallel bars and two spaces of equal width and separation
3.2
group number
number of square dots preceding the array of elements which is used to locate a position on the tribar resolving-
power target
3.3
tribar resolving-power target
array of identical elements that decrease in size (geometrically), and typically spirals towards the centre of the
target format
3.4
spatial period
within an element of a tribar target, the distance between the leading edges of two consecutive bars
NOTE The spatial period is usually expressed in millimetres (mm).
© ISO 2000 – All rights reserved 1
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ISO 6328:2000(E)
3.5
spatial frequency
reciprocal of the spatial period denoting the number of identical bar and space pairs that can be contained within an
overall width of 1 mm
NOTE The spatial frequency is expressed as reciprocal millimetres (cycles per millimetre).
3.6
contrast ratio
ratio of the luminances of the bars of the element to the luminance of the surround or the antilog of the density
difference between the bar and its surround
3.7
target polarity
transmission relationship of the parallel bars and their surround
3.7.1
negative polarity
light bars against a dark surround
3.7.2
positive polarity
dark bars against a light surround
3.8
camera
optical system by which the tribar resolving-power target is imaged and recorded, with suitable reduction in size, on
the photographic material being tested
3.9
reference surface
flat surface against which the emulsion side of the photographic material is pressed during exposure
3.10
qualification
�camera�
attainment of the necessary high optical performance of a camera, essential for its use in determining resolving
power
3.11
replicate set
series of images of the tribar resolving-power target made at the same focus and exposure settings
3.12
exposure series
series of images made at different exposure settings
3.13
focus series
series of images made at different focus settings
3.14
resolving power
ability of a photographic material to maintain, in the developed image, the separate identity of parallel bars when
their separation is small
NOTE The resolving power is numerically equal to the spatial frequency of the smallest element that can be resolved.
2 © ISO 2000 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 6328:2000(E)
3.15
limiting element
that element in the image of the tribar resolving-power target selected by the observer, with reasonable confidence,
to be at the threshold of no longer being able to distinguish three bars and two spaces, even if the number were not
known to be three
3.16
resolving power of a replicate set
median of the resolving powers of the test material in images of the replicate set
3.17
maximum resolving power
resolving power of the test material under conditions of optimum focus and exposure and the test conditions
defined in this International Standard
3.18
ISO resolving power
averaged maximum resolving power, rounded according to Table 5 and ISO 497
NOTE There is an ISO high-contrast and an ISO low-contrast resolving power.
4 Sampling and storage
In determining the resolving power of a product, it is important that the samples evaluated yield the average results
obtained by users. This will require evaluating several different batches periodically under the conditions specified
in this International Standard.
Prior to evaluation, the samples shall be stored according to the manufacturer’s recommendations for a length of
time that simulates the average age at which the product is normally used. When no specific recommendation is
made, storage shall comply with the specifications of ISO 554, 23 °C � 2 °C and a relative humidity of (50 � 5) %.
Several independent evaluations shall be made to ensure the proper calibration of equipment and processes. The
basic objective in selecting and storing samples as described above is to ensure that the material characteristics
are representative of those obtained by a consumer at the time of use.
5 Test method
5.1 Principle
The resolving power of a material is determined by visual inspection of the image of the tribar resolving-power
target recorded on the test material by means of a suitable camera system. It depends on the contrast ratio,
polarity and exposure. The resolving power passes through a maximum as the exposure is changed from a value
at the toe of the characteristic curve to a value toward the shoulder. Furthermore, the resolving power passes
through a maximum as the focus setting is given successive values that vary from one side of the correct focus to
the other.
In brief, the procedure is to first determine the exposure that gives the best-resolved image of the tribar resolving-
power target, using the focus setting determined during the camera qualification test. A through focus series is
then run at this exposure level to optimize focus. The maximum resolving power obtained from this series is used
to determine the ISO resolving power of a sample using the scale defined in Table 5.
Because of the granular structure of the image when viewed under magnification, a replicate set often yields a
range of resolving power values. To mitigate the effect of this variable, ISO resolving power is defined below in
terms of the median value of a set of not less than nine replicate images made at the same focus and exposure
setting.
© ISO 2000 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 6328:2000(E)
Microscopic examination and readout of the tribar target's image is required to determine resolving power. Since
the technique involves observer judgment in determining the finest element resolved, experience has shown that,
without application of the procedures of this International Standard, observers may differ by more than a factor of
two in the resolving power value they assign to the same image.
NOTE No known set of calibrated images exists for training and definition purposes.
Accordingly, this International Standard provides a set of guidelines that, when applied, has been shown to
produce consistent results within and between observers. With training and use of these guidelines, experienced
observers should agree to within � 1 element or about � 12 % (in terms of cycles per millimetre) for single-point
estimates, and � 6 % for mean estimates with a standard deviation of � 6%.
5.2 Apparatus
5.2.1 Element
The element shall be three parallel bars and two spaces of equal width and separation, inscribed in a square as
shown in Figure 1. For a negative-polarity target, the shaded part of Figure 1 represents the darker portion, and
the unshaded part the lighter portion, of the field of view. The bar length to width aspect ratio shall be 5:1. In terms
of displacement L (period distance in millimetres) of the bars and interspaces, the dimensions of the square are
2,5 Lx2,5 L. The shaded part of Figure 1 is termed the "surround".
The width of the bars and the width of the interspaces shown in Figure 1 shall be within � 2,5 % of the aim value.
The overall width and length of the element (2,5 L) shall also be within � 2,5 % of the aim value.
Figure 1 — Element test pattern
The spatial frequency, expressed as reciprocal millimetres, of the element may be calculated by one of the
methods described in a) or b) below. Selection is based upon the measurement instrumentation that provides the
highest dimensional accuracy within the distances being measured.
a) By measuring the bar interspace distance, or period L, in millimetres, and applying the formula:
1
Spatial frequency =
L
b) By measuring the overall element width (2,5 L), in millimetres, and applying the formula:
25,
Spatial frequency =
Overall element width
4 © ISO 2000 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 6328:2000(E)
5.2.2 Tribar resolving-power target
The tribar resolving-power target shall be an array of elements as illustrated in Figure 2.
The spatial frequencies of the elements in the array shall be as shown in Table 1. The change in spatial frequency
0,05
between successive elements shall be equal to 10 . This corresponds to increments of about 12 %.
The tribar resolving-power target shall be a spectrally non-selective neutral transparency.
The array of elements in Figure 2 is approximately 100 mm square and is centred in a surround that is about
125 mm square. The two horizontal lines are 100 mm � 0,5 mm apart and are used to determine the magnification.
The luminance of the three bars of each element and the luminance of the surround shall be measured at the
position of the eyepiece which serves as the imaging lens.
NOTE A spot photometer may be used to measure the luminance of the surround and that of the largest bars to verify the
contrast ratio of the tribar resolving-power target in the resolving-power camera. Since it will not be feasible to measure the
luminance of the smaller bars with the spot photometer, a micro-densitometer may be used to verify the contrast uniformity of
the target from the largest to the smallest elements.
This International Standard specifies tribar resolving-power targets of two different contrast ratios and polarities.
Although a negative-polarity tribar resolving-power target has light bars on a darker background, for the sake of
clarity of reproduction, this figure shows the bars black against a white background.
Figure 2 — Tribar resolving-power target
© ISO 2000 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO 6328:2000(E)
Table 1 — Spatial frequency of elements
Values of frequency in reciprocal millimetres
Group number
Element within
the group
1 234567
1 0,100 0,200 0,398 0,794 1,58 3,16 6,31
2 0,112 0,224 0,447 0,891 1,78 3,55 7,08
3 0,126 0,251 0,501 1,00 2,00 3,98 7,94
4 0,141 0,282 0,562 1,12 2,24 4,47
5 0,158 0,316 0,631 1,26 2,51 5,01
6 0,178 0,355 0,708 1,41 2,82 5,62
–1
NOTE The entries are the values of L in reciprocal millimetres for the 39 elements in
the tribar resolving-power target of Figure 2. The number of square dots in Figure 2 indicates
the group number. A convenient way to identify each element for recording purposes is to
use the form 3/2, where 3 is the group number and 2 indicates the second element in that
group.
5.2.2.1 High-contrast tribar resolving-power target
For the high-contrast tribar resolving-power target, the common logarithm of the contrast ratio shall be at least 2,0.
This is equivalent to a contrast ratio of 100:1 or greater.
5.2.2.2 Low-contrast tribar resolving-power target
For the low-contrast tribar resolving-power target, the common logarithm of the contrast ratio shall be 0,20
�� �0,02
...
SLOVENSKI STANDARD
SIST ISO 6328:2003
01-april-2003
)RWRJUDILMD)RWRJUDIVNLPDWHULDOL8JRWDYOMDQMHORþOMLYRVWLSR,62
Photography -- Photographic materials -- Determination of ISO resolving power
Photographie -- Surfaces sensibles -- Détermination du pouvoir résolvant ISO
Ta slovenski standard je istoveten z: ISO 6328:2000
ICS:
37.040.20 )RWRJUDIVNLSDSLUILOPLLQ Photographic paper, films
IRWRJUDIVNHSORãþH)LOPVNL and cartridges
]YLWNL
SIST ISO 6328:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 6328:2003
---------------------- Page: 2 ----------------------
SIST ISO 6328:2003
INTERNATIONAL ISO
STANDARD 6328
Second edition
2000-05-01
Corrected and reprinted
2000-09-01
Photography — Photographic materials —
Determination of ISO resolving power
Photographie — Surfaces sensibles — Détermination du pouvoir résolvant
ISO
Reference number
ISO 6328:2000(E)
©
ISO 2000
---------------------- Page: 3 ----------------------
SIST ISO 6328:2003
ISO 6328:2000(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not
be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this
file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this
area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters
were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event
that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2000
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body
in the country of the requester.
ISO copyright office
Case postale 56 � CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.ch
Web www.iso.ch
Printed in Switzerland
ii © ISO 2000 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 6328:2003
ISO 6328:2000(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Sampling and storage .3
5 Test method.3
6 Product classification .13
7 Product marking and labelling .14
Annex A (informative) Illustration of an example of a resolving-power camera .15
© ISO 2000 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 6328:2003
ISO 6328:2000(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
International Standard ISO 6328 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 6328:1982), which has been technically revised.
In this revision, the description of the process of evaluating images has been expanded. The specifications of the
resolving power camera’s objectives have been altered slightly, and the illustration of a resolving-power camera
has been moved to informative annex A. The text describing qualification of the camera has been expanded to
include the target.
This second edition also contains many other changes, most of which were made for the sake of clarity of
understanding. Among these changes is a clarification of part of the scope. The definitions have also been
expanded; some terms have been substituted for others in order for their usage to be more consistent and their
meaning to be clearer. The term “element” has been introduced in place of “test pattern” and “tribar resolving-
power target” replaces “test chart”. Other terms introduced or clearly defined include “target polarity”, “limiting
element” and “ISO resolving power”.
Annex A of this International Standard is for information only.
iv © ISO 2000 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 6328:2003
ISO 6328:2000(E)
Introduction
The resolving power of a photographic material is used to estimate the smallest detail that may be visually
observable when recorded on the material. It combines the effects of modulation transfer function, graininess and
contrast, all of which contribute to overall image quality, and human observers, each of whom may differ in their
assessment of quality. The method is particularly useful for appraising materials that will be viewed at high
magnification such as microfilm, 8 mm and 16 mm motion picture film, etc. However, resolving power should not
be expected to predict overall image quality in every situation, because image quality is too complex to be
described by a single factor. This is particularly the case for low-contrast continuous-tone products.
Resolving power as measured by photographing suitable tribar resolving-power targets is very dependent on
conditions of measurement, and the structure of the target element. It depends markedly on the photographic
conditions employed and on the presence of background glare from the illuminated target. It is affected by such
factors as the spectral content of the light used, the exposure level, the focus, processing procedures, the lens
aperture at which the test is made, the contrast of the target and the magnification of the camera lens and the
microscope through which the images are observed, etc.
The judgment exercised by the human observer in determining resolving power can be a source of significant
experimental error. The criterion of resolution given in this International Standard was selected because it
appeared to admit less latitude in interpretation than others. The description of the process of evaluating images
has been expanded in this revision.
© ISO 2000 – All rights reserved v
---------------------- Page: 7 ----------------------
SIST ISO 6328:2003
---------------------- Page: 8 ----------------------
SIST ISO 6328:2003
INTERNATIONAL STANDARD ISO 6328:2000(E)
Photography — Photographic materials — Determination of ISO
resolving power
1 Scope
This International Standard specifies a method for determining the resolving power of photographic films, plates
and papers, including black-and-white films, black-and-white printing papers, colour-reversal films, colour-negative
films, and colour-printing papers.
Materials designed for X-ray and other high-energy radiation are excluded, as are photographic materials used in
medical radiography where the exposure source is an intensifying screen in contact with the film (sensitized on one
or two sides). Also excluded are materials having photo-polymer, diazo, etc. light-sensitive layers.
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 497:1973, Guide to the choice of series of preferred numbers and of series containing more rounded values of
preferred numbers.
ISO 554:1976, Standard atmospheres for conditioning and/or testing — Specifications.
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1
element
three parallel bars and two spaces of equal width and separation
3.2
group number
number of square dots preceding the array of elements which is used to locate a position on the tribar resolving-
power target
3.3
tribar resolving-power target
array of identical elements that decrease in size (geometrically), and typically spirals towards the centre of the
target format
3.4
spatial period
within an element of a tribar target, the distance between the leading edges of two consecutive bars
NOTE The spatial period is usually expressed in millimetres (mm).
© ISO 2000 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST ISO 6328:2003
ISO 6328:2000(E)
3.5
spatial frequency
reciprocal of the spatial period denoting the number of identical bar and space pairs that can be contained within an
overall width of 1 mm
NOTE The spatial frequency is expressed as reciprocal millimetres (cycles per millimetre).
3.6
contrast ratio
ratio of the luminances of the bars of the element to the luminance of the surround or the antilog of the density
difference between the bar and its surround
3.7
target polarity
transmission relationship of the parallel bars and their surround
3.7.1
negative polarity
light bars against a dark surround
3.7.2
positive polarity
dark bars against a light surround
3.8
camera
optical system by which the tribar resolving-power target is imaged and recorded, with suitable reduction in size, on
the photographic material being tested
3.9
reference surface
flat surface against which the emulsion side of the photographic material is pressed during exposure
3.10
qualification
�camera�
attainment of the necessary high optical performance of a camera, essential for its use in determining resolving
power
3.11
replicate set
series of images of the tribar resolving-power target made at the same focus and exposure settings
3.12
exposure series
series of images made at different exposure settings
3.13
focus series
series of images made at different focus settings
3.14
resolving power
ability of a photographic material to maintain, in the developed image, the separate identity of parallel bars when
their separation is small
NOTE The resolving power is numerically equal to the spatial frequency of the smallest element that can be resolved.
2 © ISO 2000 – All rights reserved
---------------------- Page: 10 ----------------------
SIST ISO 6328:2003
ISO 6328:2000(E)
3.15
limiting element
that element in the image of the tribar resolving-power target selected by the observer, with reasonable confidence,
to be at the threshold of no longer being able to distinguish three bars and two spaces, even if the number were not
known to be three
3.16
resolving power of a replicate set
median of the resolving powers of the test material in images of the replicate set
3.17
maximum resolving power
resolving power of the test material under conditions of optimum focus and exposure and the test conditions
defined in this International Standard
3.18
ISO resolving power
averaged maximum resolving power, rounded according to Table 5 and ISO 497
NOTE There is an ISO high-contrast and an ISO low-contrast resolving power.
4 Sampling and storage
In determining the resolving power of a product, it is important that the samples evaluated yield the average results
obtained by users. This will require evaluating several different batches periodically under the conditions specified
in this International Standard.
Prior to evaluation, the samples shall be stored according to the manufacturer’s recommendations for a length of
time that simulates the average age at which the product is normally used. When no specific recommendation is
made, storage shall comply with the specifications of ISO 554, 23 °C � 2 °C and a relative humidity of (50 � 5) %.
Several independent evaluations shall be made to ensure the proper calibration of equipment and processes. The
basic objective in selecting and storing samples as described above is to ensure that the material characteristics
are representative of those obtained by a consumer at the time of use.
5 Test method
5.1 Principle
The resolving power of a material is determined by visual inspection of the image of the tribar resolving-power
target recorded on the test material by means of a suitable camera system. It depends on the contrast ratio,
polarity and exposure. The resolving power passes through a maximum as the exposure is changed from a value
at the toe of the characteristic curve to a value toward the shoulder. Furthermore, the resolving power passes
through a maximum as the focus setting is given successive values that vary from one side of the correct focus to
the other.
In brief, the procedure is to first determine the exposure that gives the best-resolved image of the tribar resolving-
power target, using the focus setting determined during the camera qualification test. A through focus series is
then run at this exposure level to optimize focus. The maximum resolving power obtained from this series is used
to determine the ISO resolving power of a sample using the scale defined in Table 5.
Because of the granular structure of the image when viewed under magnification, a replicate set often yields a
range of resolving power values. To mitigate the effect of this variable, ISO resolving power is defined below in
terms of the median value of a set of not less than nine replicate images made at the same focus and exposure
setting.
© ISO 2000 – All rights reserved 3
---------------------- Page: 11 ----------------------
SIST ISO 6328:2003
ISO 6328:2000(E)
Microscopic examination and readout of the tribar target's image is required to determine resolving power. Since
the technique involves observer judgment in determining the finest element resolved, experience has shown that,
without application of the procedures of this International Standard, observers may differ by more than a factor of
two in the resolving power value they assign to the same image.
NOTE No known set of calibrated images exists for training and definition purposes.
Accordingly, this International Standard provides a set of guidelines that, when applied, has been shown to
produce consistent results within and between observers. With training and use of these guidelines, experienced
observers should agree to within � 1 element or about � 12 % (in terms of cycles per millimetre) for single-point
estimates, and � 6 % for mean estimates with a standard deviation of � 6%.
5.2 Apparatus
5.2.1 Element
The element shall be three parallel bars and two spaces of equal width and separation, inscribed in a square as
shown in Figure 1. For a negative-polarity target, the shaded part of Figure 1 represents the darker portion, and
the unshaded part the lighter portion, of the field of view. The bar length to width aspect ratio shall be 5:1. In terms
of displacement L (period distance in millimetres) of the bars and interspaces, the dimensions of the square are
2,5 Lx2,5 L. The shaded part of Figure 1 is termed the "surround".
The width of the bars and the width of the interspaces shown in Figure 1 shall be within � 2,5 % of the aim value.
The overall width and length of the element (2,5 L) shall also be within � 2,5 % of the aim value.
Figure 1 — Element test pattern
The spatial frequency, expressed as reciprocal millimetres, of the element may be calculated by one of the
methods described in a) or b) below. Selection is based upon the measurement instrumentation that provides the
highest dimensional accuracy within the distances being measured.
a) By measuring the bar interspace distance, or period L, in millimetres, and applying the formula:
1
Spatial frequency =
L
b) By measuring the overall element width (2,5 L), in millimetres, and applying the formula:
25,
Spatial frequency =
Overall element width
4 © ISO 2000 – All rights reserved
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SIST ISO 6328:2003
ISO 6328:2000(E)
5.2.2 Tribar resolving-power target
The tribar resolving-power target shall be an array of elements as illustrated in Figure 2.
The spatial frequencies of the elements in the array shall be as shown in Table 1. The change in spatial frequency
0,05
between successive elements shall be equal to 10 . This corresponds to increments of about 12 %.
The tribar resolving-power target shall be a spectrally non-selective neutral transparency.
The array of elements in Figure 2 is approximately 100 mm square and is centred in a surround that is about
125 mm square. The two horizontal lines are 100 mm � 0,5 mm apart and are used to determine the magnification.
The luminance of the three bars of each element and the luminance of the surround shall be measured at the
position of the eyepiece which serves as the imaging lens.
NOTE A spot photometer may be used to measure the luminance of the surround and that of the largest bars to verify the
contrast ratio of the tribar resolving-power target in the resolving-power camera. Since it will not be feasible to measure the
luminance of the smaller bars with the spot photometer, a micro-densitometer may be used to verify the contrast uniformity of
the target from the largest to the smallest elements.
This International Standard specifies tribar resolving-power targets of two different contrast ratios and polarities.
Although a negative-polarity tribar resolving-power target has light bars on a darker background, for the sake of
clarity of reproduction, this figure shows the bars black against a white background.
Figure 2 — Tribar resolving-power target
© ISO 2000 – All rights reserved 5
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SIST ISO 6328:2003
ISO 6328:2000(E)
Table 1 — Spatial frequency of elements
Values of frequency in reciprocal millimetres
Group number
Element within
the group
1 234567
1 0,100 0,200 0,398 0,794 1,58 3,16 6,31
2 0,112 0,224 0,447 0,891 1,78 3,55 7,08
3 0,126 0,251 0,501 1,00 2,00 3,98 7,94
4 0,141 0,282 0,562 1,12 2,24 4,47
5 0,158 0,316 0,631 1,26 2,51 5,01
6 0,178 0,355 0,708 1,41 2,82 5,62
–1
NOTE The entries are the values of L in reciprocal millimetres for the 39 elements in
the tribar resolving-power target of Figure 2. The number of square dots in Figure 2 indicates
the group number. A convenient way to identify each element for recording purposes is to
us
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