SIST ISO 12232:2011

INTERNATIONAL ISO
STANDARD 12232
Second edition
2006-04-15
Corrected version
2006-10-01
Photography — Digital still cameras —
Determination of exposure index, ISO
speed ratings, standard output
sensitivity, and recommended exposure
index
Photographie — Appareils de prises de vue numériques —
Détermination de l'indice d'exposition, des régimes de vitesse ISO, de
la sensibilité normale de sortie et de l'indice d'exposition recommandé

Reference number
©
ISO 2006
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ii © ISO 2006 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Exposure index values.3
4.1 General.3
4.2 Focal plane measurement.3
4.3 Scene luminance measurement.3
5 Test conditions .4
5.1 General.4
5.2 Illumination.4
5.2.1 Daylight illumination .4
5.2.2 Tungsten illumination .4
5.3 Temperature and relative humidity.5
5.4 White balance.5
5.5 Infrared (IR) blocking filter.5
5.6 Photosite integration time .5
5.7 Compression.5
5.8 Other DSC user settings .5
6 Determination of ISO speed.5
6.1 General.5
6.2 Saturation-based speed .6
6.2.1 Focal plane measurement.6
6.2.2 Scene luminance measurement.6
6.3 Noise-based speed .6
6.3.1 Focal plane method .6
6.3.2 Scene luminance method .7
6.3.3 Colour cameras.7
6.3.4 Quantization effects.8
6.4 Method of reporting.8
7 Determination of standard output sensitivity (SOS).8
7.1 Method for calculating SOS.9
7.2 Method of reporting.9
8 Specification of recommended exposure index (REI) .9
8.1 Method for calculating recommended exposure index .9
8.2 Method of reporting.10
Annex A (informative) Recommended procedure for determining the noise-based ISO speed.11
Annex B (informative) Scene luminance and focal plane exposure .13
Annex C (informative) Recommended procedure for determining SOS values .14
Annex D (normative) Removing low frequency variations from the image data.15
Annex E (informative) Calculation of noise-based minimum illumination level.16
Bibliography .17

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 12232 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 12232:1998), which has been technically
revised.
This corrected version incorporates the following corrections:
⎯ the normative reference ISO 7589 has been dated;
⎯ the symbol for the effective f-number of the lens has been made consistent in Equations (2), (3) and (4);
⎯ the cross-references in the column headings have been corrected in Table 1;
⎯ Figure A.1 has been changed and notes and footnotes have been added for better clarity;
⎯ Equation (B.1) has been corrected and the symbol for the vignetting factor changed;
⎯ the second paragraph in Annex D has been reworded and changed to a note to reflect its intentional
informative nature;
⎯ the second sentence in Table D.1 has been slightly reworded and added at the end of the paragraph
preceding Table D.1;
⎯ in Table D.1, zeros have been added to values to improve their readability and the text below the values
has been changed to Note 1 to show its intentional informative nature;
⎯ a note has been added to both Figure A.1 and Table D.1 to notify the reader that the decimal sign is a
comma in accordance with ISO 31-0;
⎯ ISO 31-0 has been added to the Bibliography and the references have been renumbered accordingly.
iv © ISO 2006 – All rights reserved

Introduction
The ISO speed rating, standard output sensitivity (SOS) and recommended exposure index (REI) are
important attributes of digital still cameras (DSCs). Standardization assists users and manufacturers in
obtaining proper exposures and in determining the low light capability of DSCs.
The exposure level of a DSC is determined by the exposure time, the lens aperture, the lens transmittance,
the level and spectral distribution of the scene illumination, and the scene reflectance. When an image from a
DSC is obtained using an insufficient exposure, proper tone reproduction can generally be maintained by
increasing the electronic or digital gain, but the image will contain an unacceptable amount of noise. As the
exposure is increased, the gain can be decreased, and, therefore, the image noise can normally be reduced
to an acceptable level. If the exposure is increased excessively, the resulting signal in bright areas of the
image may exceed the maximum signal level capacity of the image sensor or camera signal processing. This
can cause the image highlights to be clipped to form a uniformly bright area, or to bloom into surrounding
areas of the image. Therefore, it is important to guide the user in setting proper exposures. An ISO speed
rating is intended to serve as such a guide. The methods for assigning an ISO speed rating to a DSC
harmonize with current film-based photographic standards. In order to be easily understood by photographers,
the ISO speed rating for a DSC should directly relate to the ISO speed rating for photographic film cameras.
For example, if a DSC has an ISO speed rating of ISO 100, then the same exposure time and aperture should
be appropriate for an ISO 100 rated film/process system.
The ISO speed ratings described in this International Standard are intended to harmonize with film ISO speed
ratings. However, there are differences between electronic and film-based imaging systems that preclude
exact equivalency. DSCs can include variable gain and can provide digital processing after the image data
has been captured, enabling desired tone reproduction to be achieved over a range of camera exposures. It is
therefore possible for DSCs to have a range of speed ratings. This range is defined as the ISO speed latitude.
To prevent confusion, a single value is designated as the ISO speed, with the ISO speed latitude upper and
lower limits indicating the speed range.

INTERNATIONAL STANDARD ISO 12232:2006(E)

Photography — Digital still cameras — Determination of
exposure index, ISO speed ratings, standard output sensitivity,
and recommended exposure index
1 Scope
This International Standard specifies the method for assigning and reporting ISO speed ratings, ISO speed
latitude ratings, standard output sensitivity values, and recommended exposure index values, for digital still
cameras. This International Standard is applicable to both monochrome and colour digital still cameras.
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 554, Standard atmospheres for conditioning and/or testing — Specifications
ISO 7589:2002, Photography — Illuminants for sensitometry — Specifications for daylight, incandescent
tungsten and printer
ISO 14524, Photography — Electronic still-picture cameras — Methods for measuring opto-electronic
conversion functions (O
...