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1、BRITISH STANDARD BS ISO 12232:1998 Photography Electronic still-picture cameras Determination of ISO speed ICS 37.040.10 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12232:1998 This British Standard, having been prepared under the
2、direction of the Consumer Products and Services Sector Committee, was published under the authority of the Standards Committee and comes into effect on 15 November 1998 BSI 05-1999 ISBN 0 580 30678 X National foreword This British Standard reproduces verbatim ISO 12232:1998 and implements it as the
3、UK national standard. The UK participation in its preparation was entrusted to Technical Committee CPW/42, Photography, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals
4、 for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement internatio
5、nal or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include a
6、ll the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i an
7、d ii, the ISO title page, pages ii to iv, pages 1 to 13 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.DateComments Li
8、censed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12232:1998 BSI 05-1999i Contents Page National forewordInside front cover Forewordiii Text of ISO 122321 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Unc
9、ontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12232:1998 ii BSI 05-1999 Contents Page Forewo
10、rdiii Introduction1 1Scope1 2Normative references2 3Definitions2 4Exposure index values3 5Test conditions4 6Determination of ISO speed5 Annex A (informative) Recommended procedure for determining the noise-based ISO speed10 Annex B (informative) Scene luminance and focal plane exposure11 Annex C (in
11、formative) Calculation of noise-based minimum illumination level12 Annex D (informative) Bibliography12 Figure A.111 Table 1 ISO speed and ISO speed latitude reported values9 Descriptors: Photography, photographic equipment, electronic equipment, electronic imaging, cameras, still cameras, tests, de
12、termination, exposure. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12232:1998 BSI 05-1999iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodi
13、es). 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
14、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. Draft International Standards adopted by the technical committees are circulated to the member bodi
15、es for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard ISO 12232 was prepared by Technical Committee ISO/TC 42, Photography. Annex A, Annex B, Annex C and Annex D of this International Standard are for in
16、formation only. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patents. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 200
17、6, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12232:1998 BSI 05-19991 Introduction The ISO speed rating is an important attribute of photographic systems. Standardization assists users and manu
18、facturers in obtaining proper exposures and in determining the low light capability of electronic still cameras. The camera exposure is determined by the exposure time, the lens aperture, the lens transmittance, the level and colour temperature of the scene illumination, and the scene reflectance. W
19、hen an image from an electronic still-picture camera is obtained using an insufficient exposure, proper tone reproduction can generally be maintained by increasing the electronic gain, but the image will contain an unacceptable amount of noise. As the exposure is increased, the gain can be decreased
20、, 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 highlight
21、s 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 exposures properly. An ISO speed rating is intended to serve as such a guide. The methods for assigning an ISO speed rating to electronic cameras
22、should harmonize with current photographic standards and practice. In order to be easily understood by photographers, the ISO speed rating for an electronic camera should directly relate to the ISO speed rating for photographic film cameras. For example, if an electronic camera has an ISO speed rati
23、ng 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 for electronic cameras described in this International Standard are intended to harmonize with ISO speed ratings for films. However, there are differences bet
24、ween electronic and film imaging systems that preclude exact equivalency in use. Cameras with variable gain, and digital processing after the data has been captured, allow desired tone reproduction to be achieved over a range of camera exposures. It is therefore possible for electronic cameras to ha
25、ve a range of speed ratings.1) This range is defined as the ISO speed latitude. To prevent confusion, a single value is designated as the ISO speed, with the upper and lower limits of the ISO speed latitude indicating the speed range. The camera measurements described in this International Standard
26、are performed in the digital domain, using digital analysis techniques. For electronic cameras that include only analog outputs, the analog signal should be digitized, so that the digital measurement can be performed. The digitizing equipment should be characterized, so that the effects of the digit
27、ization can be removed from the measurement results. When this is not possible, the type of digitizing equipment used should be reported along with the measurement results. Since the noise performance of an image sensor may vary significantly with exposure time and operating temperature, these opera
28、ting conditions are specified. The visibility of noise to human observers depends on the magnitude of the noise, the apparent tone of the area containing the noise, and the spatial frequency of the noise. The magnitude of the noise present in an output representation depends on the noise present in
29、the stored image data and the contrast amplification or gain applied to the data in producing the output. The noise visibility is different for the luminance (or monochrome) channel and the colour (or colour difference) channels. Therefore, this International Standard accounts for these factors in m
30、easuring the noise-based speed and speed latitude values. 1 Scope This International Standard specifies a method for assigning exposure index values, ISO speed ratings, and ISO speed latitude ratings to electronic still-picture cameras. The standard applies to both monochrome and colour electronic s
31、till-picture cameras. 1) While it is also possible to use many films at a variety of camera exposures, the behaviour of film is fundamentally different from that of electronic sensors. For example, significant underexposure typically results in uncorrectable tone reproduction errors in film-based ph
32、otographic systems. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12232:1998 2 BSI 05-1999 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this Intern
33、ational Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below.
34、Members of IEC and ISO maintain registers of currently valid International Standards. ISO 554:1976, Standard atmospheres for conditioning and/or testing Specifications. ISO 2721:1982, Photography Cameras Automatic controls of exposure. ISO 7589:1984, Photography Illuminants for sensitometry Specific
35、ations for daylight and incandescent tungsten. ISO 14524:, Photography Electronic still-picture cameras Methods for measuring opto-electronic conversion functions (OECFs)2). ITU-R BT.709:1993, Basic parameter values for the HDTV standard for the studio and for international programme exchange. 3 Def
36、initions For the purposes of this International Standard, the following definitions apply. 3.1 electronic still-picture camera camera incorporating an image sensor that outputs an analog or digital signal representing a still picture, and/or records an analog or digital signal representing a still p
37、icture on a removable media, such as a memory card or magnetic disk 3.2 exposure index numerical value that is inversely proportional to the exposure provided to an image sensor to obtain an image. Images obtained from a camera using a range of exposure index values will normally provide a range of
38、image quality levels 3.3 exposure series series of images of the same subject taken using different exposure index values 3.4 image sensor electronic device that converts incident electromagnetic radiation into an electronic signal; for example, a charge-coupled device (CCD) array 3.5 ISO speed nume
39、rical value calculated from the exposure provided at the focal plane of an electronic camera to produce specified camera output signal characteristics using the methods described in this International Standard. The ISO speed should correlate with the highest exposure index value that provides peak i
40、mage quality for normal scenes 3.6 ISO speed latitude set of two numerical values calculated from the exposure provided at the focal plane of an electronic camera to produce specified camera output signal characteristics using the methods described in this International Standard. The ISO speed latit
41、ude should correlate with the range of exposure index values that provide acceptable image quality for normal scenes 2) To be published. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 12:59:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 12232:1998 BSI 05-19993 3.7 photosite integration
42、 time total time period during which the photosites of an image sensor are able to integrate the light from the scene to form an image 3.8 signal processing operations performed by electronic circuits or algorithms that convert or modify the output of an image sensor 4 Exposure index values An expos
43、ure index (EI) is a numerical value that is inversely proportional to the exposure provided to an image sensor to obtain an image. Images obtained from a camera, using a range of EI values, will normally provide a range of image quality levels. The ISO speed of an electronic still-picture camera is
44、equal to a particular exposure index value calculated from the exposure provided at the focal plane of an electronic camera to produce specified camera output signal characteristics using the methods described in this International Standard. The equations used in this International Standard have bee
45、n chosen to create a link between electronic and conventional silver halide based photographic systems. Using a particular ISO speed value as the exposure index on an electronic still camera should result in the same camera exposure settings, and resulting focal plane exposures, as would be obtained
46、 using the same exposure index on a film camera or other photographic exposure meter. 4.1 Focal plane measurement For electronic still (or other) camera exposure meters, where the arithmetic mean focal plane exposure is measured within a circle lying in the centre of the image with a diameter of 75/
47、100 times the shorter dimension of the image field, the exposure index values should be computed using equation (1), as described in ISO 2721. where Ha is the arithmetic mean focal plane exposure, in lux seconds3)4). 4.2 Scene luminance measurement For electronic still (or other) camera exposure met
48、ers where the arithmetic mean scene luminance is measured, the expected value of the arithmetic mean focal plane exposure required in equation (1) can be computed using equation (2). The derivation of equation (2) is given in Annex B. where . . .(1) 3) Note that the value of 10 as the constant in eq
49、uation (1) is consistent with ISO 2721 and ISO 5763. These International Standards assume that the exposure is an arithmetic mean value, as is normally provided by a camera light meter. If the geometric mean exposure was used in place of the arithmetic mean exposure, a lower value for this constant would be appropriate. Note that the arithmetic mean exposure is obtained when the linear exposure values are averaged, while a geometric mean exposure is obtained by taking the antilog of the average of the logarithmic exposure values. An approximation to the