1、BSI Standards PublicationBS ISO 17957:2015Photography Digital cameras Shading measurementsBS ISO 17957:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 17957:2015. The UK participation in its preparation was entrusted to TechnicalCommittee CPW/42, Photograp
2、hy.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2015.Published by BSI Sta
3、ndards Limited 2015ISBN 978 0 580 78304 3 ICS 37.040.01 Compliance with a British Standard cannot confer immunity from legal obligations.This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 April 2015.Amendments/corrigenda issued since publicat
4、ionDate T e x t a f f e c t e d ISO 2015Photography Digital cameras Shading measurementsPhotographie Camras numriques Mesurages dombrageINTERNATIONAL STANDARDISO 17957First edition 2015-04-01Reference number ISO 17957:2015(E)BS ISO 17957:2015ISO 17957:2015(E)ii ISO 2015 All rights reservedCOPYRIGHT
5、PROTECTED DOCUMENT ISO 2015All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission.
6、Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 17957:2015ISO 1795
7、7:2015(E)Foreword ivIntroduction v1 Scope . 12 Normative references 13 Terms and definitions . 14 Test conditions and methods . 14.1 General . 14.2 Apparatus and hardware 24.3 Lighting 24.4 Test chart 24.5 Image/camera settings 25 Analytical approach. 35.1 General . 35.2 Lightness non-uniformity 45.
8、3 Luminance non-uniformity 45.4 Chrominance non-uniformity 55.5 Total colour non-uniformity 56 Presentations of results 5Annex A (normative) Recommended measurement condition 7Annex B (informative) Example of shading metric calculation 8Bibliography .13 ISO 2015 All rights reserved iiiContents PageB
9、S ISO 17957:2015ISO 17957:2015(E)ForewordISO (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 inter
10、ested 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
11、 Commission (IEC) on all matters of electrotechnical standardization.The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO docume
12、nts should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).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
13、 for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name used in this document is information given for th
14、e convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT), see the following URL: F
15、oreword Supplementary information .The committee responsible for this document is ISO/TC 42, Photography.iv ISO 2015 All rights reservedBS ISO 17957:2015ISO 17957:2015(E)IntroductionOne common type of image phenomenon seen in digital cameras is a systematic intensity variation across an image known
16、as luminance shading. There are several causes of luminance shading in a digital camera: pixels having non-uniform sensitivity across a sensor array, illumination non-uniformity, lens shading, pixel geometry, and electronic non-uniformity. Characteristics of lens shading include symmetry about the o
17、ptical sensor, uniformity across each colour plane, and variation as a function of cosn. Luminance shading only affects intensity falloff.Colour variations within the image can be induced by several factors, all of which will cause varying degrees of non-neutrality within an ideal uniform-gray expos
18、ure. Some of the primary factors include, (a) a mismatch between the CMOS micro-lens optical acceptance angle and the lens chief ray angle over the field of view, (b) spatially varying spectral transmittance differences from the infrared rejection filter (usually most significant at the cutoff wavel
19、ength), and (c) inherent spectral sensitivity differences across the array. Consistent, systematic variations can be reduced through correction via image processing, but there might remain residual colour variations.The information that follows defines the recommended approach for creating a test sc
20、ene to use for the evaluation of luminance shading and colour variations, as well as specifying the conditions for illumination and exposure. The currently proposed analysis approach to quantify the magnitude of colour variations is described. It is important to understand that this specification is
21、 related to the degree of colour variations that are apparent in the image, not the specific colour accuracy. Thus, an image that appeared pink but was uniformly pink over the entire image would be equivalent to a perfectly uniform gray field relative to this colour non-uniformity specification.Some
22、 part of this International Standard is based on the work done by the Camera Phone Image Quality group (CPIQ) within the International Imaging Industry Association (I3A), now part of the Institute of Electrical and Electronics Engineers (IEEE), whose contribution is greatly acknowledged. ISO 2015 Al
23、l rights reserved vBS ISO 17957:2015BS ISO 17957:2015Photography Digital cameras Shading measurements1 ScopeThis International Standard defines a method for measuring shading for digital cameras (including camera phones). The method includes procedures for measuring colour and luminance signal compo
24、nents separately.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (inc
25、luding any amendments) applies.ISO 7589, Photography Illuminants for sensitometry Specifications for daylight, incandescent tungsten and printerISO 11664-2/CIE, S 014-2/E: Joint ISO/CIE Standard: Colourimetry Part 2: CIE Standard Illuminants for ColourimetryISO 11664-4/CIE, S 014-4/E: Joint ISO/CIE
26、Standard: Colourimetry Part 4: CIE 1976 L*a*b* Colour SpaceISO 12231, Photography Electronic still picture imaging VocabularyIEC 61966-2-1:1999+A1:2003: Multimedia systems and equipment Colour measurement and management Part 2-1: Colour management Default RGB colour space sRGBCIE 15:2004, Colourimet
27、ry3 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.3.1luminance shading luminance non-uniformitygradual variation of the luminance signal components within the image field3.2colour shading colour non-uniformitygradual variation of the chrominance si
28、gnal components within the image field4 Test conditions and methods4.1 GeneralThe following measurement conditions should be used as nominal conditions when measuring the shading of a digital camera. If it is not possible or appropriate to achieve these nominal operating conditions, the actual opera
29、ting conditions shall be listed along with the reported results.INTERNATIONAL STANDARD ISO 17957:2015(E) ISO 2015 All rights reserved 1BS ISO 17957:2015ISO 17957:2015(E)4.2 Apparatus and hardwareThe following hardware is necessary to control and report the test conditions: a uniform field target; li
30、ght source(s); luminance meter.The total uniformity required for the target and for the light source(s) is specified below.4.3 LightingFor lightness non-uniformity and luminance non-uniformity measurement, average outdoor daylight (type D) illuminant shall be used. For chrominance non-uniformity mea
31、surement and total colour non-uniformity measurement, three standard illuminants shall be used to represent the characteristics of (a) average outdoor daylight (type D), (b) indoor incandescent lighting (type A), and (c) indoor fluorescent lighting (type F). Other illuminants may be used optionally.
32、 The type of illuminant shall be reported in any case.The recommended daylight illuminant is CIE/D55 (5 503K) with a tolerance of 5 000K to 6 504K. The recommended indoor incandescent illuminant is CIE/A (2 856K) with a tolerance of 2 700K to 3 200K. The recommended fluorescent illuminant is type CI
33、E/F2 (4 230K) with a tolerance of 3 900K to 4 600K.The light source(s) shall be positioned to provide uniform illumination and produce no glare or reflections from the target.4.4 Test chartThe target shall provide a spectrally neutral, uniform luminance distribution over the entire imaged field of v
34、iew. Spectral neutrality is achieved if the spectral transmittance or reflectance of the target does not vary by more than 5 % over the range between 420 nm and 750 nm. The construction of the target can be either transmissive or reflective. Total luminance uniformity of the lighting and the test ch
35、art is very important for this measurement. The luminance uniformity should be within 2,5 %; (i.e. |Max-Ave|/Ave =()+0 008 8567 787 16 116 0 008if 88560 008 8567 78713fYiY Yi YYiYfYiY Ynn nn() () () ,() ,(= =ifiiY Yi YfZiZ Zi ZZiZnnnn)/ () ,() () ()()+=16 116 0 008 85613ififnnfZiZ Zi iZ()=()+0 008 8
36、567 787 16 116 0 008 856,() ,()/ () ,if(4)5.2 Lightness non-uniformityThe lightness non-uniformity, DL,is defined as:DLiLiL=max ()min()*(5)5.3 Luminance non-uniformityThe luminance non-uniformity, DY(%), is defined as:DYi YiYiY=max ()min()max ()100 (6)4 ISO 2015 All rights reservedBS ISO 17957:2015I
37、SO 17957:2015(E)5.4 Chrominance non-uniformityAnalysis of the chrominance non-uniformity is performed by first calculating the overall average a * and b * for the entire image using the block average values: ai*() and bi*().amai bmbiimim*() *()= =11(7)wherem is the number of measurement blocks.The c
38、hrominance deviation of the ith block is calculated by:Di ai biabc()=()+()*22(8)The chrominance non-uniformity, DC,is defined as the maximum deviation from the overall average as:DDicc= max() (9)5.5 Total colour non-uniformityAnalysis of total colour non-uniformity begins by first calculating the ov
39、erall maximums and minimums of L*(i), a*(i), and b*(i).LLiL Limaxminmaxmin*,=()=()(10)amax ai amin aimaxmin*,=()=()(11)bmax bi bmin bimaxmin*,=()=()(12)The total colour non-uniformity, DTotal,is calculated as:DLLaabbTotalmax minmax minmax min=()+()+()* * *222(13)6 Presentations of resultsThe followi
40、ng measurement conditions shall be reported for each model. If a condition is unknown, write “unknown” Model name/Number: _ F-Number: _ Focal length: _ Focus distance: _ ISO sensitivity: _ Exposure time: _ Average output level of central measurement block: _ ISO 2015 All rights reserved 5BS ISO 1795
41、7:2015ISO 17957:2015(E)Following measurement conditions shall be reported for each metric. Light source: D/A/F (or other)6 ISO 2015 All rights reservedBS ISO 17957:2015ISO 17957:2015(E)Annex A (normative) Recommended measurement conditionThe following measurement conditions are recommended when the
42、representative values for the shading property of the camera are necessary. It is recommended to report the metric when the shading properties are most noticeable (i.e. the worst case). However, since it is almost impossible to find the worst value for every shooting condition, the recommended measu
43、rement condition in this Annex may alternatively be used.Aperture stopaat the smallest F-number (i.e. largest aperture)Focal lengthbat the shortest focal length (i.e. wide-end)aInformative The luminance shading property at the smallest F-number tends to be the largest.bInformative The luminance shad
44、ing property at the shortest focal length tends to be the largest.When the shading properties of several cameras are compared, it is meaningful to conduct measurements with the same F-number, Focal length, and Focus distance.For the case of settings not mentioned above, refer to the test conditions
45、described in Clause 4. For the camera settings that are not mentioned anywhere in this International Standard, it is recommended to use manufacturers default setting. ISO 2015 All rights reserved 7BS ISO 17957:2015ISO 17957:2015(E)Annex B (informative) Example of shading metric calculationB.1 Genera
46、lThe following example is provided to demonstrate the methodology for assessing the shading properties and for computing the lightness, luminance, chrominance, and total non-uniformity metrics of an image.B.2 Calculation of non-uniformity metricsThe measurement algorithm used in this International S
47、tandard assumes an RGB image is acquired of a uniform-field target with materials and methods as defined in 4.3 to 4.5. The following conversions assume the usual case that the image is stored in the sRGB colour space defined in IEC 61966-2-1:1999.a) For this example, the image is sub-sectioned into
48、 (2N+1) (2N+1) blocks per 5.1, with N = 5, yielding an image containing 11 11 blocks.b) The RGB values are averaged, per channel, to obtain average red, green, and blue values for each of the 11 11 measurement blocks as defined by Formula 1. The results for this step of the calculation are provided in Table B.1. The averaged sRGB values are converted to Linear RGB values per Formula 2.c) The tristimulus values X(i), Y(i), and Z(i), are calculated from the linear RGB values per Formula 3. The tristimulus values calculated per Formula
