ISO 10505:2009

INTERNATIONAL ISO
STANDARD 10505
First edition
2009-05-15


Photography — Root mean square
granularity of photographic films —
Method of measurement
Photographie — Moyenne quadratique granulaire de films
photographiques — Méthode de mesure





Reference number
ISO 10505:2009(E)
©
ISO 2009

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ISO 10505:2009(E)
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ISO 10505:2009(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Measurement instrument . 3
4.1 General. 3
4.2 Microdensitometer. 3
4.3 Spectral products . 6
4.4 Spatial frequency response. 7
4.5 Scanning motion. 7
5 Instrument electronics . 8
5.1 Conversion to density . 8
5.2 Temporal frequency response of the instrument. 8
5.3 Instrument noise . 8
6 Diffuse rms-granularity . 8
6.1 Optical geometry. 8
6.2 Diffuse conversion factor g. 9
7 Preparation of specimens. 9
7.1 Sampling and storage . 9
7.2 Exposure. 10
7.3 Processing. 10
7.4 Specimen uniformity . 10
7.5 Sampled area. 10
8 Operation of the measurement instrument. 10
8.1 Positioning the specimen . 10
8.2 Specimen scanning . 10
8.3 Control of focus . 10
8.4 Rate of scan. 11
8.5 Density mode . 11
9 Method of test . 11
9.1 Principle. 11
9.2 Statistical background . 11
9.3 Construction of the median estimator and the 95 % confidence intervals. 12
9.4 Instrument noise . 13
9.5 Diffuse rms-granularity . 14
9.6 Uncertainty of the rms-granularity result. 14
9.7 Reporting results . 14
9.8 Summary of rms-granularity characterization parameters . 15
Annex A (informative) Typical viewing magnifications for critical naked-eye viewing . 16
Annex B (informative) Limiting the temporal frequency response of the measuring instrument . 18
Annex C (informative) The effects of specimen non-uniformity. 20
Annex D (informative) Derived constants c for subgroup sizes 10, 20, …, 200 . 21
Annex E (informative) Determination of sample size for specified precision and subgroup size. 22
Bibliography . 24

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ISO 10505:2009(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 10505 was prepared by Technical Committee ISO/TC 42, Photography.
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ISO 10505:2009(E)
Introduction
This International Standard specifies procedures for measuring and computing the root mean square
granularity (rms-granularity) of photographic films. Its purpose is to provide guidance in making accurate
measurements, and also to provide an objective basis for comparing films. This International Standard
describes a method for making accurate rms-granularity measurements in the presence of instrument noise
and minor sample imperfections.
In principle, the measurement of rms-granularity is straightforward, but its determination with accuracy is not a
trivial matter. Experience has shown that the preparation of an imperfection-free sample is virtually impossible
in usual practice. Therefore, considerable attention has been devoted to the definition of a method of
accurately estimating the rms-granularity of a film in the presence of density fluctuations not caused by the
intrinsic grain structure of the film.
Research in rms-granularity (see Reference [10]) has pointed out that the inclusion of several “artefact-
induced” data values in a set of several thousand “grain-produced” data values may result in large errors in
the rms-granularity estimate. Under these circumstances, the traditional method for estimating rms-granularity
produces higher rms-granularity estimates than the new method. It can also be shown that this method
produces results that are identical to those produced by the traditional method when using artefact-free data.
In either case, it is important to bear in mind that rms-granularity is a statistical estimate which is necessarily
reported with its associated confidence intervals. In addition, the measurement process recognizes and
accounts for the presence of instrument noise that can affect the accuracy of the rms-granularity estimate.

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INTERNATIONAL STANDARD ISO 10505:2009(E)

Photography — Root mean square granularity of photographic
films — Method of measurement
1 Scope
This International Standard describes a method for determining the intrinsic root mean square granularity
(rms-granularity) of photographic films. Intrinsic rms-granularity refers to those density fluctuations produced
solely by the distribution of developed image forming centres in the photographic emulsion.
Continuous-tone monochrome (silver absorbing species) and colour (dye absorbing species) materials coated
on a transmitting support can be measured by the procedures described in this International Standard. This
International Standard is intended for imaging systems with viewing magnifications between 5× and 12× (see
Annex A).
The following kinds of granularity measurements are not covered by this International Standard, even though
they are photographically important:
⎯ reflecting materials (photographic papers);
⎯ materials having emulsion coated on both sides of the support (e.g. some X-ray films);
⎯ the estimation of the noise power spectrum (Wiener spectrum).
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 5-3, Photography — Density measurements — Part 3: Spectral conditions
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
transmittance factor
T
ratio of the measured flux transmitted by a specimen to the measured flux when the specimen is removed
from the sampling aperture of the measuring device
φ
T
NOTE T =
φ
J
where
φ is the transmitted flux;
T
φ is the aperture flux.
J
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ISO 10505:2009(E)
3.2
transmission density
D
T
logarithm to the base 10 of the reciprocal of the transmittance factor, T
NOTE D = log 1/ T .
T 10
3.3
microtransmittance factor
transmittance factor of a small area of a film or plate, measured using a suitable instrument such as a
microphotometer
NOTE In general, the microtransmittance factor of a uniformly exposed and developed film sample varies from
point-to-point on the surface. The measured microtransmittance factor of a given film or plate can depend on the optical
geometry of the instrument in which it is measured.
3.4
microdensity
D
transform of the microtransmittance factor in accordance with the usual relation D = log 1/T
10
3.5
graininess
sensation produced, in the mind of an observer viewing a photographic image, by random inhomogeneity in
what should be structureless areas
NOTE Graininess is a subjective quantity that is necessarily measured by psychophysical methods and, as such, is
outside the scope of this International Standard.
3.6
root mean square granularity
rms-granularity
σ
D
objective characterization of the spatial microdensity fluctuation of a uniformly exposed and developed
photographic layer, determined in accordance with this International Standard
NOTE 1 See Reference [3].
NOTE 2 In contrast to graininess, rms-granularity is an objective quantity.
NOTE 3 The spatial fluctuation is observed when the microdensity of the layer is measured at various points over the
surface and is the result of the random distribution of the absorbent species in the layer. The fluctuation in the
microdensity over an area of a specimen is characterized by its standard deviation, σ , and is generally a function of the
D
specimen’s macrodensity. This quantity is termed the “rms-granularity” and in all conceivable cases of interest, this
population parameter cannot be determined exactly because of finite sample size. The method for estimating σ is
D
described in Clause 9.
NOTE 4 The relation between graininess and rms-granularity is as follows: rms-granularity is intended to be an
objective correlate of graininess. The methods of measuring film rms-granularity as defined in 3.6 have been found to give
values that generally correlate with the magnitude of the graininess sensation produced when images produced by the film
are viewed under suitable conditions. The just-noticeable differences in graininess, detectable by observers viewing areas
having a visual density of about 1,0, correspond to differences in rms-granularity of 6 % for a uniform field, of 16 % for an
[4]
average scene and of 30 % for a complex or busy scene . Because rms-granularity does not account for effects
encountered in multiple stage imaging processes, methods for evaluating the graininess of final images have been
[11]
developed . These methods are particularly useful for comparing the image graininess of different final print formats
when produced from different negative formats and film types.
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ISO 10505:2009(E)
3.7
specimen
piece of photographic film or photographic plate on which rms-granularity measurements are made
NOTE The specimen can be specific or constitute a sample from a population whose rms-granularity is being
determined.
3.8
diffuse conversion factor
g
factor used to convert small transmission (projection) density differences produced by most
microdensitometers to small diffuse density differences, as determined in accordance with 6.2
3.9
spatial frequency passband
part of the spatial frequency spectrum that passes through the measuring system
NOTE The spatial frequency passband is determined by the cut-off frequencies of the system on the low side and the
high side of the spatial frequency. The passband characteristics required for the measuring instrument are specified in 5.2.
4 Measurement instrument
4.1 General
This clause describes the basic elements of an instrument suitable for the measurement of rms-granularity.
The generic instrument described in this clause follows the general principles for a linear, incoherent
microdensitometer used in an overfilled, image-scanning mode. Microdensitometers of different designs may
be employed, provided they are shown to conform to the physical optics principles required for linearity and
incoherent illumination, as described in References [6], [7], [8] and [9].
4.2 Microdensitometer
4.2.1 Apparatus
A typical microdensitometer is shown schematically in Figure 1. Its key elements are as follows:
⎯ light source (1): an incoherent source of suitable spectral power distribution;
⎯ illumination filter (2), which produces spectral transmittance necessary to conform to 4.2.2;
⎯ condenser lens (3): optics that fill the influx aperture uniformly with light;
⎯ influx aperture (4): in the optical system shown in Figure 1, this aperture limits the area of the specimen
that is illuminated in order to minimize stray light in the optical system;
⎯ influx optics (5), which images the influx aperture (4) on the specimen at point 6;
⎯ specimen (6): emulsion (7) facing the efflux optics;
⎯ efflux optics (8), which collects the light transmitted by the specimen and focuses it upon the efflux
aperture of the instrument;
⎯ efflux (measuring) aperture (9): this aperture, projected back onto the specimen, determines the area of
the specimen whose density is being measured; its effective size at the specimen is determined by its
physical size divided by the optical magnification from the plane at point 6 to the plane at point 9;
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ISO 10505:2009(E)
⎯ collecting lens (10), which collects the light transmitted by the aperture (9) and relays it to the
photodetector;
NOTE The collecting lens is omitted in some designs.
⎯ efflux optical filter (11): spectral transmittance determined by density measurement type;
⎯ photodetector (12), which shall have a spectral responsivity consistent with the spectral products required
to produce one or more of the density measurement spectral types defined in ISO 5-3.

Key
1 light source
2 illumination filter
3 condenser lens
4 influx aperture
5 influx optics
6 specimen
7 emulsion
8 efflux optics
9 efflux (measuring) aperture
10 collecting lens
11 efflux optical filter
12 photodetector
Figure 1 — Schematic representation of a typical rms-granularity measuring microdensitometer
4.2.2 Influx spectrum
The influx spectrum for rms-granularity measurements shall be as specified for transmission densitometry in
ISO 5-3.
For transmission density measurements, if either the densitometer manufacturer or the user is not sure of the
absence of fluorescence in the sample to be measured, the relative spectral power distribution of the incident
flux S shall be that of the CIE standard illuminant A (ISO 5-3), modified in the infrared region to protect the
H
sample and optical elements from excessive heat, which is typical for most transmission densitometers.
4.2.3 Influx aperture
The influx aperture shall be circular or square in shape and its image shall be concentric with that of the efflux
aperture. When both apertures are referred to the plane of the specimen, the linear size of the influx aperture
shall not be less than 1,5 times, nor more than 2 times, the linear size of the efflux aperture.
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ISO 10505:2009(E)
4.2.4 Microdensitometer optics
4.2.4.1 General
The microscope objectives specified in 4.2.4.2 to 4.2.4.4 are the basic objectives for the measurement of
rms-granularity and shall be used unless there is a specific reason to employ objectives of different
characteristics. The use of alternate objectives is discussed in 4.2.5.3. An analysis of the effects of the
microdensitometer optics on the measurement of rms-granularity is presented in Annex B.
4.2.4.2 Influx objective
When films are being measured, the influx objective shall be a high quality microscope objective having a
numerical aperture (N ) of 0,3 ± 0,1. It shall not have the same numerical aperture as the efflux objective. If
AI
photographic plates are to be measured, the N of the influx objective shall be no greater than 0,25, and the
AI
optical system shall be carefully focused to accommodate the thickness of the glass support.
4.2.4.3 Efflux objective
The efflux objective of the microdensitometer shall be a high quality microscope objective having a numerical
aperture (N ) equal to 0,25 ± 0,10. It shall not have the same numerical aperture as the influx objective
AE
(4.2.4.4).
4.2.4.4 Mismatching the numerical apertures of the influx and efflux objectives
In order to maintain incoherence in the optical system over the spatial frequencies of interest, it is necessary
to mismatch the numerical aperture of the influx objective, N , and the numerical aperture of the efflux
AI
objective, N . The mismatch criteria are given in References [6], [7], [8] and [9] for the following two cases of
AE
interest:
⎯ Case 1: overfilled efflux objective, N > N
AI AE
NN/1>+u /u (1)
()
AI AE max co
⎯ Case 2: underfilled efflux objective, N > N
AE AI
NN/1>+u /u (2)
()
AE AI max co
where
−1
u is the maximum sample frequency (u = 100 mm );
max max
u is the spatial frequency cut-off of the objective with the smaller numerical aperture, N
co A
(i.e. u = 2N /λ).
co A
EXAMPLE If the efflux objective is underfilled and N = 0,30, then N > 0,30 (1 + 100/1 090) = 0,327 when λ
AI AE
equals 550 nm.
It can happen then that the mismatch criteria for the numerical apertures of the influx and efflux optics lead to
numerical aperture values which are outside the ranges of 0,3 ± 0,1 for the influx objective and 0,25 ± 0,10 for
the efflux objective respectively. Keeping the numerical apertures within their respective ranges would then
result in a non-linear behaviour of the microdensitometer leading to a corresponding additional uncertainty.
−1
NOTE The above-mentioned maximum sample frequency, u = 100 mm , is true for colour films. However, in the
max
case of black-and-white films, the noise power spectrum can have different contributions well beyond this limit
[18]
(e.g. microfilm) .
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ISO 10505:2009(E)
4.2.5 Objectives
4.2.5.1 Objective lens aberrations
The influx and efflux objectives may be achromatic or apochromatic; apochromatic objectives are
recommended for use with colour materials. Achromatic objectives can be used either with or without
eyepieces, depending on the optical design of the microdensitometer. If achromatic objectives are used to
scan colour films, special care shall be taken to optimize the focal settings for each individual colour response.
4.2.5.2 Eyepieces
In some cases, notably that of apochromatic objectives, the optical design is such that the objectives need to
be used with certain eyepieces for optimum results. If apochromatic objectives are used in the optical design,
they shall be used with eyepieces as directed by the manufacturer. The powers of the eyepieces used may be
varied as needed to meet the requirements for the optical magnification. When eyepieces are used, the “tube
length” (i.e. the distance between objective and eyepiece) shall be optimized for the objective and eyepiece
combination.
4.2.5.3 Use of objectives having other numerical apertures
In general, the purpose of measuring the rms-granularity of the specimen is to predict its behaviour in an
imaging application. In some cases, where the film or plate is to be used with an optical system, the numerical
apertures of the imaging system will be known and may be significantly different from the values given above.
The numerical apertures of a measurement instrument optical system can be changed to simulate a specific
imaging application more closely. However, in such cases the simulated application shall be stated and the
numerical apertures used shall also be stated.
4.2.6 Efflux aperture
The efflux aperture should be circular in shape. Alternatively, a rectangular or square aperture of similar
dimensions (resulting in the same aperture surface) can be used. The effective diameter of the image of the
circular efflux aperture at the specimen plane shall be (48,0 ± 0,5) µm when calculated via the magnification.
A 42,5 µm square image of the efflux aperture gives comparable results (within 5 %). The physical size of the
aperture may be any convenient size.
NOTE In this International Standard, further detailed analyses will all refer to circular apertures.
4.2.7 Photodetector
Any photodetector may be used in the granularity measurement instrument provided that it meets the
following requirements:
a) its spectral responsivity range covers the wavelength range of interest and is continuous over this range,
b) its frequency response is adequate to evaluate the incoming flux variations,
c) its sensitivity is sufficient for operation over the required density range (including filters for colour
materials), and
d) the electronic noise it adds to the granularity signal is stable and measurable.
4.3 Spectral products
4.3.1 Specification
The spectral product of the system will depend on the type of measurement desired. ISO 5-3 specifies the
spectral products of the types of density referenced below.
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ISO 10505:2009(E)
4.3.2 Visual density
For films on which the images are truly neutral, the spectral product used is unimportant, because all would
give the same result. However, in the interests of standardization and in recognition of the fact that most
“neutral” images are not precisely spectrally non-selective, visual density spectral products in accordance with
ISO 5-3 shall be used for such films.
Visual density may also be used for films or materials that are viewed directly or by projection (such as colour
transparencies).
4.3.3 Status M density
Status M density spectral products in accordance with ISO 5-3 shall be used for films on which spectrally
selective images are produced (even when the images are visually neutral), but which are not intended to be
viewed directly (such as colour negative films).
4.3.4 Status A density
Status A density spectral products in accordance with ISO 5-3 may be used for films which produce spectrally
selective images (even when the images are visually neutral) and which are intended to be viewed directly
(such as colour transparencies).
4.4 Spatial frequency response
4.4.1 Spatial frequency response of influx side
The spatial frequency response of the influx side of the microdensitometer is determined by the influx optical
system. It shall be of sufficient quality to provide a “hard aperture”, as defined in Reference [6].
NOTE A “hard aperture” designates an image that generally resembles the source aperture geometrically.
4.4.2 Spatial frequency response of efflux side
The total spatial frequency response of the measurement instrument efflux side is given by the product of its
efflux optical transfer function (OTF) and the transfer function of the circular or square efflux aperture. The
transfer function for a circular aperture is a Bessel function of the first kind and of order 1. The first five zero
−1 −1 −1
crossings for a 48 µm aperture function occur at frequencies of 25,4 mm , 46,5 mm , 67,4 mm ,
−1 −1
88,4 mm and 109,2 mm , respectively. The OTF includes all optical components except the efflux aperture.
The magnitude of the OTF (which is gener
...