ISO 16067-2:2004
(Main)Photography - Electronic scanners for photographic images - Spatial resolution measurements — Part 2: Film scanners
Photography - Electronic scanners for photographic images - Spatial resolution measurements — Part 2: Film scanners
ISO 16067-2:2004 specifies methods for measuring and reporting the spatial resolution of electronic scanners for continuous tone photographic negatives and reversal (e.g. slide) films. It applies to both monochrome and colour film scanners.
Photographie — Scanners électroniques pour images photographiques — Mesurages de la résolution spatiale — Partie 2: Scanners pour films
Fotografija - Elektronski skenerji za fotografske slike - Meritve prostorske ločljivosti - 2. del: Skenerji za filme
Ta del ISO 16067 določa metode za merjenje in poročanje o prostorski ločljivosti elektronskih skenerjev za negativne fotografske in obračalne filme (npr. za diapozitive) filme z neprekinjenim tonom. Ta mednarodni standard velja za skenerje za črno-bele in barvne filme.
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INTERNATIONAL ISO
STANDARD 16067-2
First edition
2004-10-15
Photography — Electronic scanners for
photographic images — Spatial
resolution measurements —
Part 2:
Film scanners
Photographie — Scanners électroniques pour images
photographiques — Mesurages de la résolution spatiale —
Partie 2: Scanners pour films
Reference number
ISO 16067-2:2004(E)
©
ISO 2004
---------------------- Page: 1 ----------------------
ISO 16067-2:2004(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 2004
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.org
Web www.iso.org
Published in Switzerland
ii © ISO 2004 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 16067-2:2004(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Test chart . 4
4.1 Representation and recommended size .4
4.2 General characteristics of the test chart . 4
4.3 Test chart elements . 6
5 Test conditions. 7
5.1 General. 7
5.2 Temperature and relative humidity . 8
5.3 Luminance and colour measurements .8
5.4 Linearization . 8
5.5 Scanner settings . 8
6 Measuring the scanner OECF. 8
7 Limiting visual resolution and its relation to SFR . 8
8 Edge SFR test measurement . 9
9 Presentation of results . 9
9.1 General. 9
9.2 Scanner OECF . 10
9.3 Resolution Measurements . 11
Annex A (normative) Scanner OECF test patches. 13
Annex B (informative) SFR algorithm. 14
Annex C (informative) Using slanted edge analysis for colour spatial registration measurement . 17
Bibliography . 19
© ISO 2004 – All rights reserved iii
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ISO 16067-2:2004(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 2.
The main task of technical committees is to prepare International Standards. 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 document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16067-2 was prepared by Technical Committee ISO/TC 42, Photography.
ISO 16067 consists of the following parts, under the general title Photography — Electronic scanners for
photographic images — Spatial resolution measurements:
Part 1: Scanners for reflective media
Part 2: Film scanners
iv © ISO 2004 – All rights reserved
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ISO 16067-2:2004(E)
Introduction
One of the most important characteristics of an electronic film scanner is the ability to capture the fine detail
found in the original film. This ability to resolve detail is determined by a number of factors, including the
performance of the scanner lens, the number of addressable photoelements in the image sensor(s) used in
the scanner, and the electrical circuits in the scanner. Different measurement methods can yield different
metrics that quantify the ability of the scanner to capture fine details.
This International Standard specifies methods for measuring the limiting visual resolution, and spatial
frequency response calculated from a slanted edge (Edge SFR) imaged by a film scanner. The scanner
measurements described in this International Standard are performed in the digital domain, using digital
analysis techniques. A test chart of appropriate size and characteristics is scanned and the resulting data is
analysed. The test chart described in this International Standard is designed specifically to evaluate
continuous tone film scanners. It is not designed for evaluating electronic still-picture cameras, video cameras,
or bi-tonal document scanners.
The edge SFR measurement method described in this International Standard uses a computer algorithm to
analyse digital image data from the film scanner. Pixel values near slanted vertical and horizontal edges are
used to compute the SFR values. The use of a slanted edge allows the edge gradient to be measured at
many phases relative to the image sensor photoelements, so that the SFR can be determined at spatial
frequencies higher than the half sampling frequency, sometimes called the Nyquist limit. This technique is
mathematically equivalent to a moving knife-edge measurement.
Part 1 of this International Standard deals with reflective media.
© ISO 2004 – All rights reserved v
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INTERNATIONAL STANDARD ISO 16067-2:2004(E)
Photography — Electronic scanners for photographic
images — Spatial resolution measurements —
Part 2:
Film scanners
1 Scope
This International Standard specifies methods for measuring and reporting the spatial resolution of electronic
scanners for continuous tone photographic negatives and reversal (e.g. slide) films. The International
Standard applies to both monochrome and colour film scanners.
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 5-2, Photography — Density Measurements — Part 2: Geometric conditions for transmission density
ISO 554, Standard atmospheres for conditioning and/or testing — Specifications
ISO 12231, Photography — Electronic still-picture cameras — Terminology
ISO 12233, Photography — Electronic still-picture cameras — Resolution Measurements
ISO 14524, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12231 and the following apply.
3.1
addressable photoelements
number of active photoelements in an image sensor
NOTE This is equal to the number of active lines of photoelements, multiplied by the number of active photoelements
per line.
3.2
aliasing
reconstructed image artefacts in sampled imaging systems where the combined spatial frequency energy of
the input image and scanner combination is significant beyond the half-sampling frequency of the scanner
NOTE These artefacts usually manifest themselves as moiré patterns in repetitive image features or as jagged stair
stepping at edge transitions.
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ISO 16067-2:2004(E)
3.3
digital output level
numerical value assigned to a particular output level, also known as the digital code value
3.4
edge spread function
ESF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely sharp edge
3.5
effectively spectrally neutral
having spectral characteristics that result in a specific imaging system producing the same output as for a
spectrally neutral object
3.6
electronic scanner for photographic films
scanner incorporating an image sensor that outputs a digital signal representing a still film image
3.7
fast scan direction
scan direction corresponding to the direction of the alignment of the addressable photoelements in a linear
array image sensor
3.8
gamma correction
process that alters the image data in order to modify the tone reproduction
3.9
image sensor
electronic device that converts incident electromagnetic radiation into an electronic signal; e.g. a charge
coupled device (CCD) array
3.10
resolution
measure of the ability of a digital image capture system, or a component of a digital image capture system, to
capture fine spatial detail
NOTE Resolution measurement metrics include resolving power, limiting visual resolution, SFR, MTF and CTF.
3.11
sampled imaging system
imaging system or device which generates an image signal by sampling an image at an array of discrete
points, or along a set of discrete lines, rather than a continuum of points
NOTE The sampling at each point is done using a finite size sampling aperture or area.
3.12
sample spacing
physical distance between sampling points or sampling lines, measured in units of distance (e.g. µm, mm)
NOTE The sample spacing may be different in the two orthogonal sampling directions.
3.13
sampling frequency
reciprocal of sample spacing
NOTE Expressed in samples per unit distance (e.g. dots per inch).
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ISO 16067-2:2004(E)
3.14
scanner
electronic device that converts a fixed image, such as a film or film transparency, into an electronic signal
3.15
scanner opto-electronic conversion function
scanner OECF
relationship between the input density and the digital output levels for an opto-electronic digital capture system
3.16
slow scan direction
direction in which the scanner moves the photoelements (perpendicular to the lines of active photoelements in
a linear array image sensor)
3.17
spatial frequency response
SFR
R
SFR
measured amplitude response of an imaging system as a function of relative input spatial frequency
NOTE 1 The SFR is normally represented by a curve of the output response to an input sinusoidal spatial luminance
distribution of unit amplitude, over a range of spatial frequencies. The SFR is normalized to yield a value of 1,0 at a spatial
frequency of 0.
NOTE 2 In equations, the symbol R rather than the abbreviation SFR is used for clarity.
SFR
3.18
spectrally neutral
test chart in which the relative spectral power distributions of the incident and reflected (or transmitted) light
are equal
3.19
test chart
arrangement of test patterns designed to test particular aspects of an imaging system
3.20
test pattern
specified arrangement of spectral reflectance or transmittance characteristics used in measuring an image
quality attribute
3.21
test pattern types
3.21.1
bi-tonal patterns
patterns that are spectrally neutral or effectively spectrally neutral, and consist exclusively of two reflectance
or transmittance values in a prescribed spatial arrangement
NOTE Bi-tonal patterns are typically used to measure resolving power, limiting resolution and SFR.
3.21.2
grey scale patterns
patterns that are spectrally neutral or effectively spectrally neutral, and consist of a large number of different
reflectance or transmittance values in a prescribed spatial arrangement
NOTE Grey scale patterns are typically used to measure opto-electronic conversion functions.
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ISO 16067-2:2004(E)
3.21.3
spectral patterns
patterns that are specified by the spatial arrangement of features with differing spectral reflectance or
transmittance values
NOTE Spectral patterns are typically used to measure colour reproduction.
4 Test chart
4.1 Representation and recommended size
This clause defines the type and specifications of the test chart depicted in Figure 1. This test chart can be
made at various sizes to correspond to popular film sizes. The recommended size is 24 mm × 36 mm, which
corresponds to the 35 mm film format.
Figure 1 — Representation of the test chart
4.2 General characteristics of the test chart
4.2.1 The test chart shall be a transmission test chart based on a current monochrome photographic film
material. The film material shall be spectrally neutral with tolerances as specified in ISO 14524, and resistant
to fading.
4.2.2 The active height and width of the reflection test chart should be no less than 16,7 mm. Additional
white space may be added to the width or height to include target management data or other test chart
elements not defined by this International Standard.
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ISO 16067-2:2004(E)
4.2.3 The test chart shall include grey scale patterns and should include bitonal elements. Grey scale
patches are necessary to measure the opto-electronic transfer function of the scanner. The bitonal elements
may be used to assess limiting visual resolution and aliasing. (See Clause 7.)
4.2.4 The density values of the grey patches shall be in accordance with Annex A. The densities shall be
measured as specified in ISO 5-2.
4.2.5 The target manufacturer should state the spatial frequency at which the target’s frequency content is
0,2. These declarations should be cited in both cycles per millimetre (cycles/mm) and equivalent dots-per-inch
(DPI), where the DPI value equals 50,8 times the spatial frequency in cycles/mm. Suggested wording is, “This
target suitable for SFR measurements to XXX cycles per millimetre (xxx dpi)”.
The spatial frequency content of the edge features should be the same for both near horizontal, near-vertical,
and near-45º edge features, and should be indicated as a graph (Figure 2), or should be characterized with a
closed form equation or equations up to the frequency having a 0,2 modulation response.
An example equation corresponding to Figure 2 is the N-th order polynomial:
1 2 3 4 5 6 7
Target Modulation = C + C ν + C ν + C ν + C ν + C ν + C ν + C ν (1)
0 1 2 3 4 5 6 7
Where ν = spatial frequency in terms of line pairs per millimetre
th
C = polynomial coefficients associated with the i term
i
0 −2 −3 −4
C = × 10 C = −1,0161e × 10 C = −5,9389e × 10 C = 5,6116e × 10
0 1,0000e 1 2 3
−5 −7 −9 −11
C = −2,3443e × 10 C = 5,0997e × 10 C = −5,6120e × 10 C = 2,4681e × 10
4 5 6 7
The above-mentioned 7th order polynomial is only valid, as an example frequency response characteristic, for
spatial frequencies in the range DC to approximately 58,154 1 cycles/mm.
Key
X frequency (cycles/mm)
Y modulation
Figure 2 — Frequency content of a transmission edge’s spatial derivative
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ISO 16067-2:2004(E)
4.3 Test chart elements
4.3.1 General
For testing purposes, the test chart shall include elements to measure the scanner opto-electronic conversion
function, and SFR in the fast scan and slow scan directions. (See Figure 3.)
Figure 3 — Test chart elements labelled by section number
4.3.2 Grey scale patches for measuring the scanner OECF
The test chart shall include 20 neutral grey scale patches with specified visual densities. The maximum patch
density shall be at least 1,5 times the maximum density of the central slanted square (4.2.2). The minimum
patch density shall be equal to the transmissive media minimum density. The spatial arrangement of the
patches shall be designed to minimize flare between adjacent patches as depicted in Figure 1. A suggested
spatial arrangement is given in Annex A.
4.3.3 Near-vertical and near-horizontal slanted edges to measure the vertical and horizontal edge
SFR
The test chart shall include a slanted (approximately 5º) square feature used to measure vertical and
horizontal edge SFR. The density of the square shall exceed that of the immediate surrounding area. The
central square’s surround density shall have a visual diffuse density of greater than or equal to 0,40 and less
than or equal to 0,60. The square patch density shall have a visual diffuse density of greater than or equal to
1,5 and less than or equal to 2,4.
NOTE These values insure sufficiently low edge transition contrasts to aid robust SFR measurements.
6 © ISO 2004 – All rights reserved
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ISO 16067-2:2004(E)
4.3.4 Near-45º edges to measure 45º SFR
The test chart should include a diamond shaped feature (approximately 50º from vertical) to measure the SFR
at 45º. The density of this feature should match that of the surround area defined in 4.3.2.
4.3.5 Vertical and horizontal square wave features
The test chart shall include horizontal and vertical square wave features of extended length to aid in the visual
detection of aliasing. These features shall have a spatial frequency of 25, 33,3, 50, 100, and 166,7 cycles/mm.
The minimum and maximum densities should nominally match the D and D of the grey scale patches.
max min
NOTE The square wave features have a spatial frequency corresponding to approximately 1200, 1600, 2400, 5000
and 8400 DPI.
4.3.6 Near-vertical and near-horizontal square features
The test chart shall include horizontal and vertical square wave features of extended length to aid in the
detection of aliasing. These features shall have the same frequencies as indicated in 4.3.4. The minimum and
maximum densities should nominally match the D and D of the grey scale patches.
max min
NOTE These slanted lines eliminate the ambiguity of phase-induced patterns in resolution measurements.
4.3.7 Fiducial marks to aid in automatic SFR and scanner OECF measurement
The test chart should include fiducial marks in the corners of the central target features. These marks can aid
in the automatic analysis of grey patch and slanted edge features for scanner OECF and SFR measurements.
NOTE The vertical and horizontal distance between fiducial marks in Figure 1 is 12,19 mm. This distance can be
used to verify scanner sampling frequency.
4.3.8 Slightly Slanted Extended Lines to check scan linearity, “stair stepping” and cyclical scan
artefacts
The test chart should include horizontal and vertical slightly slanted lines to check scan linearity, and cyclical
scanner behaviours such as colour channel misregistration.
4.3.9 Bi-tonal spatial resolution elements
The test chart should include bi-tonal spatial patterns to aid in evaluating limiting visual resolution. These
elements should be of high contrast (D and D ) and accompanied with numbered groups that are keyed
max min
to know spatial frequencies.
4.3.10 Administrative elements
The test chart should include administrative elements to aid in tracking the genealogy and characteristics of
the test chart being used. These may be items such as manufacturer's insignia, creation date or barcode that
aids in populating metadata elements.
5 Test conditions
5.1 General
The following measurement conditions should be used as nominal conditions when measuring the scanner
OECF and spatial resolution. If it is not possible or appropriate to achieve these nominal operating conditions,
the actual operating conditions shall be listed along with the reported results.
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ISO 16067-2:2004(E)
5.2 Temperature and relative humidity
The ambient temperature during the acquisition of the test data shall be (23 ± 2)°C, as specified in ISO 554,
and the relative humidity should be (50 ± 20) %.
5.3 Luminance and colour measurements
For a colour scanner, the spatial resolution measurements should be performed separately on each colour
record. If desired, a luminance resolution measurement may be made on a luminance signal formed from an
appropriate combination of the colour records. In either case, the channel on which the measurement is
performed shall be reported.
5.4 Linearization
The scanner output signal will likely be a non-linear function of the film density values. Linearization is
accomplished by applying the inverse of the scanner OECF to the output signal via a lookup table or
appropriate equation, and then converting from density to reflectance. The measurement of the scanner
OECF shall be as specified in Clause 6.
5.5 Scanner settings
The spatial resolution should be measured with the manufacturer’s recommended default settings. If different
settings are used, they shall be reported.
6 Measuring the scanner OECF
The scanner OECF shall be calculated from values determined from the same chart and the same scan as the
values for the resolution measurements. Many scanners will automatically adapt to the dynamic range and the
luminance distribution of the film. The results may also differ if the scan mode is grey scale or RGB.
A minimum of four trials shall be conducted for each resolution measurement and scanner OECF
determination. A trial shall consist of one scan of the test chart. For each trial, the digital output level shall be
1)
determined from a 64 × 64 pixel area located at the same relative position in each patch. Identical, non-
aligned patches may be averaged, or the patch with the least scanning artefacts, such as dust or scan lines,
may be used. The scanner OECF so determined shall be used to calculate the resolution measurements for
this trial. If the scanner OECF is reported, the final digital output level data presented for each step density
shall be the mean of the digital output levels for all the trials.
7 Limiting visual resolution and its relation to SFR
To determine the limiting visual resolution, the image of the test target is reproduced on a monitor or hard
copy film, and the visual resolution is subjectively judged. To ensure that the monitor or hard copy filmer does
not reduce the visual resolution value, the digital image may be enlarged by pixel replication prior to viewing or
filming, so that the individual pixels are visible. Observers should be well acquainted with the appearance of
aliasing, so that they do not seriously misjudge the visual resolution of the scanner. The test chart includes
vertical and horizontal elements that are used to perform this test. The limiting visual resolution is the lowest
value of the test pattern where the individual black and white lines can no longer be distinguished, or are
reproduced at a spatial frequency lower than the spatial frequency of the corresponding area of the test chart,
as a result of aliasing. The limiting visual resolution value shall not exceed the half sampling frequency. The
limiting visual resolution in the fast scan direction is normally determined by observing the vertical elements.
The visual resolution in the slow scan direction is normally determined by observing the horizontal elements. A
1) It is possible that with very low resolution scans the images of the test chart patches will not be large enough to
contain a 64 × 64 pixel area. In this case, the sample area should be slightly smaller than the image of the patch area so
that the effects of imaging the patch edge are not included.
8 © ISO 2004 – All rights reserved
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ISO 16067-2:2004(E)
very good correlation between limiting visual resolution and the spatial frequency associated with a 0,10 SFR
response has been found experimentally. Should this frequency exceed the half-sampling frequency, the
limiting visual resolution shall be the spatial frequency associated with the half-sampling frequency.
8 Edge SFR test measurement
The SFR of a film scanner is measured by analysing the scanner data near a slanted edge transition. The
near-vertical edges shown in Figure 1 are normally used to measure the SFR in the fast scan direction, and
the near-horizontal edges are normally used to measure the SFR in the slow scan direction. The SFR
measurement can be performed automatically by image processing software. To perform the measurement,
the scanner output data along the edges of the slanted square in the middle of the test chart are analysed by
a mathematical algorithm.
The SFR algorithm is given in Annex B. A flow chart form and a diagram depicting the key steps of the SFR
algorithm, and sample C-code, is described in ISO 12233. The SFR algorithm can be implemented as part of
2)
an easy-to-use image processing or analysis software package . The algorithm can automatically compute
and report the SFR, using image data from a user-defined rectangular region of the image that represents a
vertically-oriented slanted edge, depicting a “horizontal” transition. To measure the SFR in the orthogonal
direction, a horizontally-oriented edge is used, and the digital image data is rotated 90º before performing the
calculation. If the image is a colour image, the algorithm performs calculations on the separate red, green and
blue colour image records. The image code values are linearized by inverting the scanner OECF, and
converting the film densities to reflectances.
Next, for each line of pixels perpendicular to the edge, the edge is differentiated using the discrete derivative
“-0,5; +0,5”, meaning that the derivative value for pixel “X” is equal to -1/2 times the value of the pixel
immediately to the left, plus 1/2 times the value of the pixel to the right. The centroid of this derivative is
calculated to determine the position of the e
...
SLOVENSKI STANDARD
SIST ISO 16067-2:2011
01-julij-2011
)RWRJUDILMD(OHNWURQVNLVNHQHUML]DIRWRJUDIVNHVOLNH0HULWYHSURVWRUVNH
ORþOMLYRVWLGHO 6NHQHUML]DILOPH
Photography - Electronic scanners for photographic images - Spatial resolution
measurements - Part 2: Film scanners
Photographie - Scanners électroniques pour images photographiques - Mesurages de la
résolution spatiale - Partie 2: Scanners pour films
Ta slovenski standard je istoveten z: ISO 16067-2:2004
ICS:
37.040.10 Fotografska oprema. Photographic equipment.
Projektorji Projectors
SIST ISO 16067-2:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 16067-2:2011
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SIST ISO 16067-2:2011
INTERNATIONAL ISO
STANDARD 16067-2
First edition
2004-10-15
Photography — Electronic scanners for
photographic images — Spatial
resolution measurements —
Part 2:
Film scanners
Photographie — Scanners électroniques pour images
photographiques — Mesurages de la résolution spatiale —
Partie 2: Scanners pour films
Reference number
ISO 16067-2:2004(E)
©
ISO 2004
---------------------- Page: 3 ----------------------
SIST ISO 16067-2:2011
ISO 16067-2:2004(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 2004
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.org
Web www.iso.org
Published in Switzerland
ii © ISO 2004 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 16067-2:2011
ISO 16067-2:2004(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Test chart . 4
4.1 Representation and recommended size .4
4.2 General characteristics of the test chart . 4
4.3 Test chart elements . 6
5 Test conditions. 7
5.1 General. 7
5.2 Temperature and relative humidity . 8
5.3 Luminance and colour measurements .8
5.4 Linearization . 8
5.5 Scanner settings . 8
6 Measuring the scanner OECF. 8
7 Limiting visual resolution and its relation to SFR . 8
8 Edge SFR test measurement . 9
9 Presentation of results . 9
9.1 General. 9
9.2 Scanner OECF . 10
9.3 Resolution Measurements . 11
Annex A (normative) Scanner OECF test patches. 13
Annex B (informative) SFR algorithm. 14
Annex C (informative) Using slanted edge analysis for colour spatial registration measurement . 17
Bibliography . 19
© ISO 2004 – All rights reserved iii
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SIST ISO 16067-2:2011
ISO 16067-2:2004(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 2.
The main task of technical committees is to prepare International Standards. 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 document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16067-2 was prepared by Technical Committee ISO/TC 42, Photography.
ISO 16067 consists of the following parts, under the general title Photography — Electronic scanners for
photographic images — Spatial resolution measurements:
Part 1: Scanners for reflective media
Part 2: Film scanners
iv © ISO 2004 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 16067-2:2011
ISO 16067-2:2004(E)
Introduction
One of the most important characteristics of an electronic film scanner is the ability to capture the fine detail
found in the original film. This ability to resolve detail is determined by a number of factors, including the
performance of the scanner lens, the number of addressable photoelements in the image sensor(s) used in
the scanner, and the electrical circuits in the scanner. Different measurement methods can yield different
metrics that quantify the ability of the scanner to capture fine details.
This International Standard specifies methods for measuring the limiting visual resolution, and spatial
frequency response calculated from a slanted edge (Edge SFR) imaged by a film scanner. The scanner
measurements described in this International Standard are performed in the digital domain, using digital
analysis techniques. A test chart of appropriate size and characteristics is scanned and the resulting data is
analysed. The test chart described in this International Standard is designed specifically to evaluate
continuous tone film scanners. It is not designed for evaluating electronic still-picture cameras, video cameras,
or bi-tonal document scanners.
The edge SFR measurement method described in this International Standard uses a computer algorithm to
analyse digital image data from the film scanner. Pixel values near slanted vertical and horizontal edges are
used to compute the SFR values. The use of a slanted edge allows the edge gradient to be measured at
many phases relative to the image sensor photoelements, so that the SFR can be determined at spatial
frequencies higher than the half sampling frequency, sometimes called the Nyquist limit. This technique is
mathematically equivalent to a moving knife-edge measurement.
Part 1 of this International Standard deals with reflective media.
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INTERNATIONAL STANDARD ISO 16067-2:2004(E)
Photography — Electronic scanners for photographic
images — Spatial resolution measurements —
Part 2:
Film scanners
1 Scope
This International Standard specifies methods for measuring and reporting the spatial resolution of electronic
scanners for continuous tone photographic negatives and reversal (e.g. slide) films. The International
Standard applies to both monochrome and colour film scanners.
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 5-2, Photography — Density Measurements — Part 2: Geometric conditions for transmission density
ISO 554, Standard atmospheres for conditioning and/or testing — Specifications
ISO 12231, Photography — Electronic still-picture cameras — Terminology
ISO 12233, Photography — Electronic still-picture cameras — Resolution Measurements
ISO 14524, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (OECFs)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12231 and the following apply.
3.1
addressable photoelements
number of active photoelements in an image sensor
NOTE This is equal to the number of active lines of photoelements, multiplied by the number of active photoelements
per line.
3.2
aliasing
reconstructed image artefacts in sampled imaging systems where the combined spatial frequency energy of
the input image and scanner combination is significant beyond the half-sampling frequency of the scanner
NOTE These artefacts usually manifest themselves as moiré patterns in repetitive image features or as jagged stair
stepping at edge transitions.
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3.3
digital output level
numerical value assigned to a particular output level, also known as the digital code value
3.4
edge spread function
ESF
normalized spatial signal distribution in the linearized output of an imaging system resulting from imaging a
theoretical infinitely sharp edge
3.5
effectively spectrally neutral
having spectral characteristics that result in a specific imaging system producing the same output as for a
spectrally neutral object
3.6
electronic scanner for photographic films
scanner incorporating an image sensor that outputs a digital signal representing a still film image
3.7
fast scan direction
scan direction corresponding to the direction of the alignment of the addressable photoelements in a linear
array image sensor
3.8
gamma correction
process that alters the image data in order to modify the tone reproduction
3.9
image sensor
electronic device that converts incident electromagnetic radiation into an electronic signal; e.g. a charge
coupled device (CCD) array
3.10
resolution
measure of the ability of a digital image capture system, or a component of a digital image capture system, to
capture fine spatial detail
NOTE Resolution measurement metrics include resolving power, limiting visual resolution, SFR, MTF and CTF.
3.11
sampled imaging system
imaging system or device which generates an image signal by sampling an image at an array of discrete
points, or along a set of discrete lines, rather than a continuum of points
NOTE The sampling at each point is done using a finite size sampling aperture or area.
3.12
sample spacing
physical distance between sampling points or sampling lines, measured in units of distance (e.g. µm, mm)
NOTE The sample spacing may be different in the two orthogonal sampling directions.
3.13
sampling frequency
reciprocal of sample spacing
NOTE Expressed in samples per unit distance (e.g. dots per inch).
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3.14
scanner
electronic device that converts a fixed image, such as a film or film transparency, into an electronic signal
3.15
scanner opto-electronic conversion function
scanner OECF
relationship between the input density and the digital output levels for an opto-electronic digital capture system
3.16
slow scan direction
direction in which the scanner moves the photoelements (perpendicular to the lines of active photoelements in
a linear array image sensor)
3.17
spatial frequency response
SFR
R
SFR
measured amplitude response of an imaging system as a function of relative input spatial frequency
NOTE 1 The SFR is normally represented by a curve of the output response to an input sinusoidal spatial luminance
distribution of unit amplitude, over a range of spatial frequencies. The SFR is normalized to yield a value of 1,0 at a spatial
frequency of 0.
NOTE 2 In equations, the symbol R rather than the abbreviation SFR is used for clarity.
SFR
3.18
spectrally neutral
test chart in which the relative spectral power distributions of the incident and reflected (or transmitted) light
are equal
3.19
test chart
arrangement of test patterns designed to test particular aspects of an imaging system
3.20
test pattern
specified arrangement of spectral reflectance or transmittance characteristics used in measuring an image
quality attribute
3.21
test pattern types
3.21.1
bi-tonal patterns
patterns that are spectrally neutral or effectively spectrally neutral, and consist exclusively of two reflectance
or transmittance values in a prescribed spatial arrangement
NOTE Bi-tonal patterns are typically used to measure resolving power, limiting resolution and SFR.
3.21.2
grey scale patterns
patterns that are spectrally neutral or effectively spectrally neutral, and consist of a large number of different
reflectance or transmittance values in a prescribed spatial arrangement
NOTE Grey scale patterns are typically used to measure opto-electronic conversion functions.
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3.21.3
spectral patterns
patterns that are specified by the spatial arrangement of features with differing spectral reflectance or
transmittance values
NOTE Spectral patterns are typically used to measure colour reproduction.
4 Test chart
4.1 Representation and recommended size
This clause defines the type and specifications of the test chart depicted in Figure 1. This test chart can be
made at various sizes to correspond to popular film sizes. The recommended size is 24 mm × 36 mm, which
corresponds to the 35 mm film format.
Figure 1 — Representation of the test chart
4.2 General characteristics of the test chart
4.2.1 The test chart shall be a transmission test chart based on a current monochrome photographic film
material. The film material shall be spectrally neutral with tolerances as specified in ISO 14524, and resistant
to fading.
4.2.2 The active height and width of the reflection test chart should be no less than 16,7 mm. Additional
white space may be added to the width or height to include target management data or other test chart
elements not defined by this International Standard.
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4.2.3 The test chart shall include grey scale patterns and should include bitonal elements. Grey scale
patches are necessary to measure the opto-electronic transfer function of the scanner. The bitonal elements
may be used to assess limiting visual resolution and aliasing. (See Clause 7.)
4.2.4 The density values of the grey patches shall be in accordance with Annex A. The densities shall be
measured as specified in ISO 5-2.
4.2.5 The target manufacturer should state the spatial frequency at which the target’s frequency content is
0,2. These declarations should be cited in both cycles per millimetre (cycles/mm) and equivalent dots-per-inch
(DPI), where the DPI value equals 50,8 times the spatial frequency in cycles/mm. Suggested wording is, “This
target suitable for SFR measurements to XXX cycles per millimetre (xxx dpi)”.
The spatial frequency content of the edge features should be the same for both near horizontal, near-vertical,
and near-45º edge features, and should be indicated as a graph (Figure 2), or should be characterized with a
closed form equation or equations up to the frequency having a 0,2 modulation response.
An example equation corresponding to Figure 2 is the N-th order polynomial:
1 2 3 4 5 6 7
Target Modulation = C + C ν + C ν + C ν + C ν + C ν + C ν + C ν (1)
0 1 2 3 4 5 6 7
Where ν = spatial frequency in terms of line pairs per millimetre
th
C = polynomial coefficients associated with the i term
i
0 −2 −3 −4
C = × 10 C = −1,0161e × 10 C = −5,9389e × 10 C = 5,6116e × 10
0 1,0000e 1 2 3
−5 −7 −9 −11
C = −2,3443e × 10 C = 5,0997e × 10 C = −5,6120e × 10 C = 2,4681e × 10
4 5 6 7
The above-mentioned 7th order polynomial is only valid, as an example frequency response characteristic, for
spatial frequencies in the range DC to approximately 58,154 1 cycles/mm.
Key
X frequency (cycles/mm)
Y modulation
Figure 2 — Frequency content of a transmission edge’s spatial derivative
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4.3 Test chart elements
4.3.1 General
For testing purposes, the test chart shall include elements to measure the scanner opto-electronic conversion
function, and SFR in the fast scan and slow scan directions. (See Figure 3.)
Figure 3 — Test chart elements labelled by section number
4.3.2 Grey scale patches for measuring the scanner OECF
The test chart shall include 20 neutral grey scale patches with specified visual densities. The maximum patch
density shall be at least 1,5 times the maximum density of the central slanted square (4.2.2). The minimum
patch density shall be equal to the transmissive media minimum density. The spatial arrangement of the
patches shall be designed to minimize flare between adjacent patches as depicted in Figure 1. A suggested
spatial arrangement is given in Annex A.
4.3.3 Near-vertical and near-horizontal slanted edges to measure the vertical and horizontal edge
SFR
The test chart shall include a slanted (approximately 5º) square feature used to measure vertical and
horizontal edge SFR. The density of the square shall exceed that of the immediate surrounding area. The
central square’s surround density shall have a visual diffuse density of greater than or equal to 0,40 and less
than or equal to 0,60. The square patch density shall have a visual diffuse density of greater than or equal to
1,5 and less than or equal to 2,4.
NOTE These values insure sufficiently low edge transition contrasts to aid robust SFR measurements.
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4.3.4 Near-45º edges to measure 45º SFR
The test chart should include a diamond shaped feature (approximately 50º from vertical) to measure the SFR
at 45º. The density of this feature should match that of the surround area defined in 4.3.2.
4.3.5 Vertical and horizontal square wave features
The test chart shall include horizontal and vertical square wave features of extended length to aid in the visual
detection of aliasing. These features shall have a spatial frequency of 25, 33,3, 50, 100, and 166,7 cycles/mm.
The minimum and maximum densities should nominally match the D and D of the grey scale patches.
max min
NOTE The square wave features have a spatial frequency corresponding to approximately 1200, 1600, 2400, 5000
and 8400 DPI.
4.3.6 Near-vertical and near-horizontal square features
The test chart shall include horizontal and vertical square wave features of extended length to aid in the
detection of aliasing. These features shall have the same frequencies as indicated in 4.3.4. The minimum and
maximum densities should nominally match the D and D of the grey scale patches.
max min
NOTE These slanted lines eliminate the ambiguity of phase-induced patterns in resolution measurements.
4.3.7 Fiducial marks to aid in automatic SFR and scanner OECF measurement
The test chart should include fiducial marks in the corners of the central target features. These marks can aid
in the automatic analysis of grey patch and slanted edge features for scanner OECF and SFR measurements.
NOTE The vertical and horizontal distance between fiducial marks in Figure 1 is 12,19 mm. This distance can be
used to verify scanner sampling frequency.
4.3.8 Slightly Slanted Extended Lines to check scan linearity, “stair stepping” and cyclical scan
artefacts
The test chart should include horizontal and vertical slightly slanted lines to check scan linearity, and cyclical
scanner behaviours such as colour channel misregistration.
4.3.9 Bi-tonal spatial resolution elements
The test chart should include bi-tonal spatial patterns to aid in evaluating limiting visual resolution. These
elements should be of high contrast (D and D ) and accompanied with numbered groups that are keyed
max min
to know spatial frequencies.
4.3.10 Administrative elements
The test chart should include administrative elements to aid in tracking the genealogy and characteristics of
the test chart being used. These may be items such as manufacturer's insignia, creation date or barcode that
aids in populating metadata elements.
5 Test conditions
5.1 General
The following measurement conditions should be used as nominal conditions when measuring the scanner
OECF and spatial resolution. If it is not possible or appropriate to achieve these nominal operating conditions,
the actual operating conditions shall be listed along with the reported results.
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5.2 Temperature and relative humidity
The ambient temperature during the acquisition of the test data shall be (23 ± 2)°C, as specified in ISO 554,
and the relative humidity should be (50 ± 20) %.
5.3 Luminance and colour measurements
For a colour scanner, the spatial resolution measurements should be performed separately on each colour
record. If desired, a luminance resolution measurement may be made on a luminance signal formed from an
appropriate combination of the colour records. In either case, the channel on which the measurement is
performed shall be reported.
5.4 Linearization
The scanner output signal will likely be a non-linear function of the film density values. Linearization is
accomplished by applying the inverse of the scanner OECF to the output signal via a lookup table or
appropriate equation, and then converting from density to reflectance. The measurement of the scanner
OECF shall be as specified in Clause 6.
5.5 Scanner settings
The spatial resolution should be measured with the manufacturer’s recommended default settings. If different
settings are used, they shall be reported.
6 Measuring the scanner OECF
The scanner OECF shall be calculated from values determined from the same chart and the same scan as the
values for the resolution measurements. Many scanners will automatically adapt to the dynamic range and the
luminance distribution of the film. The results may also differ if the scan mode is grey scale or RGB.
A minimum of four trials shall be conducted for each resolution measurement and scanner OECF
determination. A trial shall consist of one scan of the test chart. For each trial, the digital output level shall be
1)
determined from a 64 × 64 pixel area located at the same relative position in each patch. Identical, non-
aligned patches may be averaged, or the patch with the least scanning artefacts, such as dust or scan lines,
may be used. The scanner OECF so determined shall be used to calculate the resolution measurements for
this trial. If the scanner OECF is reported, the final digital output level data presented for each step density
shall be the mean of the digital output levels for all the trials.
7 Limiting visual resolution and its relation to SFR
To determine the limiting visual resolution, the image of the test target is reproduced on a monitor or hard
copy film, and the visual resolution is subjectively judged. To ensure that the monitor or hard copy filmer does
not reduce the visual resolution value, the digital image may be enlarged by pixel replication prior to viewing or
filming, so that the individual pixels are visible. Observers should be well acquainted with the appearance of
aliasing, so that they do not seriously misjudge the visual resolution of the scanner. The test chart includes
vertical and horizontal elements that are used to perform this test. The limiting visual resolution is the lowest
value of the test pattern where the individual black and white lines can no longer be distinguished, or are
reproduced at a spatial frequency lower than the spatial frequency of the corresponding area of the test chart,
as a result of aliasing. The limiting visual resolution value shall not exceed the half sampling frequency. The
limiting visual resolution in the fast scan direction is normally determined by observing the vertical elements.
The visual resolution in the slow scan direction is normally determined by observing the horizontal elements. A
1) It is possible that with very low resolution scans the images of the test chart patches will not be large enough to
contain a 64 × 64 pixel area. In this case, the sample area should be slightly smaller than the image of the patch area so
that the effects of imaging the patch edge are not included.
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very good correlation between limiting visual resolution and the spatial frequency associated with a 0,10 SFR
response has been found experimentally. Should this frequency exceed the half-sampling frequency, the
limiting visual resolution shall be the spatial frequency associated with the half-sampling frequency.
8 Edge SFR test measurement
The SFR of a film scanner is measured by analysing the scanner data near a slanted edge transition. The
near-vertical edges shown in Figure 1 are normally used to measure the SFR in the fast scan direction, and
the near-horizontal edges are normally used to measure the SFR in the slow scan direction. The SFR
measurement can be performed automatically by image processing software. To perform the measurement,
the scanner output data along the edges of the slanted square in the middle of the test chart are analysed by
a mathematical algorithm.
The SFR algorithm is given in Ann
...
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