1、BS ISO14524:2009ICS 37.040.10NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDPhotography Electronic still-picturecameras Methodsfor measuring opto-electronic conversionfunctions (OECFs)This British Standardwas published under theauthority of the StandardsPolicy
2、and StrategyCommittee on 30 June2009. BSI 2009ISBN 978 0 580 58412 1Amendments/corrigenda issued since publicationDate CommentsBS ISO 14524:2009National forewordThis British Standard is the UK implementation of ISO 14524:2009. Itsupersedes BS ISO 14524:1999 which is withdrawn.The UK participation in
3、 its preparation was entrusted to TechnicalCommittee CPW/42, Photography.A list of organizations represented on this committee can be obtained onrequest to its secretary.This publication does not purport to include all the necessary provisionsof a contract. Users are responsible for its correct appl
4、ication.Compliance with a British Standard cannot confer immunityfrom legal obligations.BS ISO 14524:2009Reference numberISO 14524:2009(E)ISO 2009INTERNATIONAL STANDARD ISO14524Second edition2009-02-15Photography Electronic still-picture cameras Methods for measuring opto-electronic conversion funct
5、ions (OECFs) Photographie Appareils de prises de vue lectroniques Mthodes de mesure des fonctions de conversion opto-lectroniques BS ISO 14524:2009ISO 14524:2009(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or vi
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10、 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2009 All rights reservedBS ISO 14524:2009ISO 14524:2009(E) ISO 2009 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 Test method
11、s. 3 4.1 General. 3 4.2 Camera OECF measurement . 4 4.3 Focal plane OECF measurement (method A) 4 4.4 Alternative focal plane OECF measurement (method B) 4 5 Illumination 5 5.1 Focal plane OECF measurement (method A) 5 5.2 Alternative focal plane (method B) and camera OECF measurement. 5 6 Test cond
12、itions . 5 6.1 Temperature and relative humidity. 5 6.2 White balance (only applicable to colour cameras) 5 6.3 Infrared-blocking (IR-blocking) filter. 6 6.4 Focus 6 7 Input . 7 7.1 Focal plane log exposures. 7 7.2 Camera OECF chart log luminances. 7 8 Data analysis . 8 9 Presentation of results. 8
13、9.1 General. 8 9.2 Tabular presentation 9 9.3 Graphical presentation. 11 Annex A (normative) ISO 14524 camera OECF test chart 13 Annex B (informative) Relevance of the ISO 7589 spectral distribution index 20 Annex C (informative) Reporting of the camera OECF in relative reflectance units. 22 Bibliog
14、raphy . 23 BS ISO 14524:2009ISO 14524:2009(E) iv ISO 2009 All rights reservedForeword 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
15、 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 cl
16、osely 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. Dr
17、aft 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 doc
18、ument may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 14524 was prepared by Technical Committee ISO/TC 42, Photography. This second edition cancels and replaces the first edition (ISO 14524:1999), which has been technically re
19、vised. BS ISO 14524:2009ISO 14524:2009(E) ISO 2009 All rights reserved vIntroduction This International Standard establishes standard methods for measuring the functional relationship between the focal plane log exposures or scene luminances, and the digital output levels of a digital camera. This i
20、nformation is required for the development and testing of digital cameras, is used in other electronic still-picture camera measurement standards and may be helpful in the processing of digital image data. An opto-electronic conversion function (OECF) measurement standard is required for several rea
21、sons, as outlined below. a) Well-established measurement methods have been used to determine the characteristic curves for television cameras, where the characteristic curve is known as the “gamma correction” curve, and for silver halide photography, where the characteristic curve is known as the “H
22、 not logged) multiplied by system incremental gain at that level 3.9 maximum exposure limit smallest exposure which produces the digital output level corresponding to the maximum detectable exposure NOTE The maximum detectable exposure is also known as the saturation or quantization ceiling. 3.10 mi
23、nimum exposure limit largest exposure below saturation which produces an incremental output signal equal in magnitude to the output noise 3.11 opto-electronic conversion function OECF relationship between the log of the input levels and the corresponding digital output levels for an opto-electronic
24、digital image capture system BS ISO 14524:2009ISO 14524:2009(E) ISO 2009 All rights reserved 3NOTE If the input log exposure points are very finely spaced and the output noise is small compared to the quantization interval, the OECF can have a step-like character. Such behaviour is an artefact of th
25、e quantization process and it is advisable to remove this by using an appropriate smoothing algorithm or by fitting a smooth curve to the data. 3.12 opto-electronic digital image capture system system which converts either a light exposure at the focal plane, or a spatial arrangement of luminances (
26、a scene) to digital information 3.13 output noise root-mean-square fluctuation about the mean in the digital output level for a constant input level 3.14 scene luminance ratio ratio of the highest (highlight) luminance value to the lowest (shadow) luminance value in a scene 3.15 time scale exposure
27、series series of exposures produced using a constant focal plane illuminance and a varying exposure time 3.16 white balance adjustment of electronic still-picture colour channel gains or image processing so that radiation with relative spectral power distribution equal to that of the scene illuminat
28、ion source is rendered as a visual neutral 4 Test methods 4.1 General This International Standard describes test methods for measuring both camera OECFs and focal plane OECFs. Camera OECFs include the effects of the camera lens and associated flare, while focal plane OECFs do not. These image-format
29、ion effects vary with the overall scene luminance ratio, the amounts of each of the different luminances present in the scene and the spatial arrangement of these luminances. This variability can be quite large and, consequently, it is possible to determine a repeatable camera OECF only for a specif
30、ic scene, such as a test chart. The camera OECF measurement method described in this International Standard allows for the determination of different camera OECFs based on test charts with different luminance ratios, but does not allow for the effects of different amounts or spatial arrangements of
31、scene luminances. The camera OECF test charts are designed to simulate the image formation effects produced by a scene with a specific luminance ratio and average distribution of luminances; however many scenes are significantly different from average. When determining camera OECFs, it is important
32、to keep in mind that the OECF characteristics measured may be quite different from those exhibited by the camera in capturing specific scenes. The reasons for inclusion of a camera OECF measurement method are as follows: a) the mandatory automatic exposure control found in some cameras precludes the
33、 determination of focal plane OECFs; b) the camera OECF measurement method allows for one-step determination of the camera system characteristics for the scene simulated by the test chart used; c) focal plane OECF values can be estimated from camera OECF values for the midtone and highlight regions
34、of most images, provided the range of interest is covered by the test chart used. The focal plane OECF is a characteristic of the camera only and is not dependent on the scene. NOTE Some cameras and/or supporting software can contain scene-dependent rendering algorithms. These algorithms are general
35、ly bypassed when performing focal plane OECF measurements because of the approximately uniform illumination incident on the focal plane. In situations where it is impossible or undesirable to bypass the rendering algorithms, it is more appropriate to perform camera OECF measurements. BS ISO 14524:20
36、09ISO 14524:2009(E) 4 ISO 2009 All rights reservedTwo methods are described for focal plane OECF measurement, although both methods should give the same result. The preferred method (method A) allows for a higher degree of accuracy than the alternative method (method B). Method B should be used only
37、 with cameras that have fixed lenses. The advantages of focal plane OECFs are as described below. Separation of the optical image formation stage from the focal plane image to output stage allows each stage of the image capture to be dealt with independently. These two stages behave quite differentl
38、y. The image formation stage is strongly scene dependent, while the focal plane image to output stage depends only on the sensor and camera electronics characteristics. On the other hand, the response of pictorial cameras tends to be highly non-linear, complicating the subsequent analysis of optical
39、 image formation effects if the focal plane OECF is not known. The analysis of camera systems is much easier if the two stages are dealt with independently. Traditionally, only the density versus log exposure relation, or characteristic curve, is measured for film. This curve is analogous to the foc
40、al plane OECF. The predominant factor affecting camera OECF values in the darker areas of a scene is the camera flare. These values are, therefore, primarily scene dependent and do not provide much information about the general camera characteristics. Focal plane OECFs cover the entire usable range
41、of the camera and are not limited by the test chart luminance ratio. The methods for measurement of the OECFs described above are given in 4.2 to 4.4. 4.2 Camera OECF measurement The OECF may be determined for the entire camera opto-electronic digital image capture system using a camera OECF test ch
42、art as defined in this International Standard. This determination is accomplished by using the camera system to capture an image of the chart under controlled conditions. It should be noted that the independent variable for the camera OECF is scene log luminance, not focal plane log exposure as with
43、 the focal plane (method A) and alternative focal plane (method B) measurement methods. 4.3 Focal plane OECF measurement (method A) This method involves the exposure of the electronic still-picture camera sensor directly to specific quantities of uniform illumination with the camera lens removed. Th
44、e illumination shall have the spectral characteristics specified in 5.1 and shall be produced by a small source at a distance, such that the largest dimensions of the source and the sensor are no greater than 1/20 the distance from the source to the sensor. In addition, reflective surfaces shall not
45、 be placed where they could cause additional illumination to be incident on the sensor. 4.4 Alternative focal plane OECF measurement (method B) If a particular electronic still-picture camera does not allow the lens to be removed, method B may be employed. This method involves the use of a uniformly
46、 emissive, approximately Lambertian target (reflective surface or illuminator), which is then imaged by the camera lens on the sensor. If method B is used, the illuminance falling on the sensor, Es, expressed in lux, shall be assumed to be as calculated from Equation (1) (see Reference 9): ts2e0,65
47、LEf= (1) where Ltis the arithmetic mean luminance of the target in candela per square metre; feis the effective f-number of the lens. If method B is used, the target shall be measured to verify that it is approximately Lambertian and uniform in luminance. Luminance readings of the target shall be wi
48、thin 2 % of the arithmetic mean value for readings BS ISO 14524:2009ISO 14524:2009(E) ISO 2009 All rights reserved 5taken normal to the target at all four corners and at the centre of the field of view of the camera, and also for readings taken at an angle of 30 to normal of the centre of the target
49、. The surface of the target shall be normal to the optical axis of the camera ( 5) when the test image is captured, and shall extend out at least 15 beyond the edge of the camera field of view. The spectral radiance characteristics of the target shall be as described in 5.2. OECFs obtained using method B of this International Standard shall be designated as such. 5 Illumination 5.1 Focal plane OECF measurement (method A) OECF measurements shall indicate whether the daylight or tungsten illuminant was used. ISO 7589 describes t
