ISO 5-2:2009

INTERNATIONAL ISO
STANDARD 5-2
Fifth edition
2009-12-01
Photography and graphic technology —
Density measurements —
Part 2:
Geometric conditions for transmittance
density
Photographie et technologie graphique — Mesurages de la densité —
Partie 2: Conditions géométriques pour la densité de transmittance

Reference number
©
ISO 2009
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© ISO 2009
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ii © ISO 2009 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Coordinate system, terminology and symbols .2
5 Distinction between ideal and realized parameters.2
6 Requirements for ISO 5 standard diffuse transmittance density.2
6.1 Geometric modes .2
6.2 Sampling aperture.3
6.3 Diffuse distribution.5
6.4 Directional distribution .5
6.5 Designation .6
7 Requirements for ISO 5 standard projection transmittance density .6
7.1 Geometric modes .6
7.2 Sampling aperture.6
7.3 Directional distributions .7
7.4 Designation .7
8 Conformance testing.7
Annex A (normative) Diffusion coefficient.8
Annex B (normative) Determining conformance with tolerances.11
Annex C (informative) Unmatched influx and efflux angles.12
Bibliography.13

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 5-2 was prepared by ISO/TC 42, Photography, and ISO/TC 130 Graphic technology, in a Joint Working
Group.
This fifth edition cancels and replaces the fourth edition (ISO 5-2:2001), which has been technically revised.
This technical revision introduces the concept of ideal and practical conditions. In the course of this technical
revision, all parts of ISO 5 have been reviewed together, and the terminology, nomenclature and technical
requirements have been made consistent across all parts.
ISO 5 consists of the following parts, under the general title Photography and graphic technology — Density
measurements:
⎯ Part 1: Geometry and functional notation
⎯ Part 2: Geometric conditions for transmittance density
⎯ Part 3: Spectral conditions
⎯ Part 4: Geometric conditions for reflection density
iv © ISO 2009 – All rights reserved

Introduction
This part of ISO 5 specifies the geometric conditions for transmittance densitometry, primarily (but not
exclusively) as practised in black-and-white and colour photography and graphic technology. This part of
ISO 5 is intended to specify geometrical conditions for the measurement of optical densities that are close to
those used in practice. Diffuse transmittance densities are, among other things, relevant for contact printing
and rating films on viewing boxes. Viewing films on light boxes is one of the most important applications where
diffuse transmittance densities are relevant. Therefore, the specified conditions for the measurement of diffuse
transmittance densities consider the properties of viewing boxes concerning diffusivity and the spectral
reflectance factor. Another important application is the measurement of the diffuse transmittance density and
hence the opaque area percentage of lithography-type black-and-white films for graphic technology. This part
of ISO 5 also describes the geometric conditions for two types of projection density. The spectral conditions
are specified in ISO 5-3.
The primary change between the first edition of this part of ISO 5 (published in 1974) and the second edition
(published in 1985) was the replacement of the integrating sphere method with a diffuser (typically “opal
glass”) as the basis for specifying ISO 5 standard diffuse transmittance density. Although any means of
diffusion that meets the specifications of this part of ISO 5 can be used, the method is often denoted simply by
the words “opal glass” in order to differentiate it from the integrating sphere method. Slightly smaller density
values are generally obtained compared to those based on the integrating sphere method because of inter-
reflections between the opal glass and the specimen. The effect is dependent on the reflectance
characteristics of the opal glass and the surface of the specimen facing the diffuser.
Diffuse transmittance density is a measure of the modulation of light by a film that is diffusely irradiated on one
side and viewed from the other, as when a film is viewed on a diffuse transparency illuminator. The geometric
conditions of projection with diffuse illumination are nearly equivalent to the conditions of viewing a film on a
diffuse illuminator, the projection lens taking the place of the eye. When film is on a diffuse illuminator or in
contact with a print material, light is inter-reflected between the film and the nearby surface. This inter-
reflection affects the density and is best taken into account in a measuring instrument by the use of an opal-
glass diffuser or integrator, rather than an integrating sphere. Apart from this fundamental reason for using
densitometers employing opal-glass diffusers, such instruments are preferred because they are more durable
and more convenient to manufacture and use.
Projection density is a measure of the modulation of light by a film that is regularly illuminated on one side and
is projected by way of a regular collection system. Equipment employing optical condensers is used to view
microfilm, motion pictures, and slides, and to make projection prints. The conditions defined in this part of
ISO 5 for projection density simulate the geometric conditions affecting the transmitting characteristics of a
small area on a negative or transparency at the centre of the frame of a typical projection system employing
condensers. The area under consideration can be defined by a small opening, known as the “sampling
aperture”, in an otherwise opaque sheet in the frame.
The measured density depends on the half-angle of the cone of incident rays and the half-angle subtended by
the projection lens at the sampling aperture. These half-angles can be indicated either in degrees or by
ƒ-numbers. Since the ƒ-number is usually marked on projection lenses, the two types of ISO 5 standard
projection density specified in this part of ISO 5 are identified by ƒ-numbers, namely ƒ/4,5 and ƒ/1,6. The ƒ/4,5
type is frequently used, since it is representative of microfilm readers. The ƒ/1,6 type is considered
representative of motion-picture projectors.
Significant changes from the fourth edition of this part of ISO 5 are explained below.
a) The terminology “transmission density” has been replaced by the term “transmittance density” for both
diffuse and projection densities. Both densities require measurements relative to the incident flux (influx),
and therefore the regular or diffuse transmittance of the specimen is measured. As explained in ISO 5-1,
the correct density term corresponding to regular transmittance is “transmittance density”.
b) A distinction is made between ideal and realized parameters for transmittance density. The definition of
ISO 5 standard transmittance density is based upon ideal values specified for each parameter. However,
actual instruments require reasonable tolerances for physical parameters, which are specified by the
realizable parameters.
vi © ISO 2009 – All rights reserved

INTERNATIONAL STANDARD ISO 5-2:2009(E)

Photography and graphic technology — Density
measurements —
Part 2:
Geometric conditions for transmittance density
1 Scope
This part of ISO 5 specifies the geometric conditions for measuring ISO 5 standard diffuse and ƒ/4,5 and ƒ/1,6
projection transmittance densities.
ISO 5 standard diffuse density is primarily applicable to measurements of photographic images to be viewed
on a transparency illuminator, or viewing box, to be contact printed, or to be projected with a system
employing diffuse illumination.
ISO 5 standard projection density is primarily applicable to measurements of photographic images to be
projected with systems employing optical condensers.
Although primarily intended for the measurement of photographic images, the densitometric methods
specified in this part of ISO 5 are often applied to optical filters and other transparent materials.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 5-1, Photography and graphic technology — Density measurements — Part 1: Geometry and functional
notation
ISO 5-3, Photography and graphic technology — Density measurements — Part 3: Spectral conditions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5-1 and the following apply.
3.1
diffusion coefficient
β
dc
measure of the diffusivity of the illuminating or receiving system
NOTE See Annex A.
3.2
transmittance
τ
ratio of the transmitted flux to the incident flux under specified geometrical and spectral conditions of
measurement
NOTE 1 In practical instruments for transmittance measurements, the incident flux
...