1、BSI Standards PublicationBS ISO 17850:2015Photography Digital cameras Geometric distortion (GD)measurementsBS ISO 17850:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 17850:2015.The UK participation in its preparation was entrusted to TechnicalCommittee C
2、PW/42, Photography.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2015. Publis
3、hed by BSI StandardsLimited 2015ISBN 978 0 580 82900 0ICS 37.040.01Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 June 2015.Amendments issued since publication
4、Date Text affectedBS ISO 17850:2015 ISO 2015Photography Digital cameras Geometric distortion (GD) measurementsPhotographie Camras numriques Mesurages de distorsion gomtrique (DG)INTERNATIONAL STANDARDISO17850First edition2015-07-01Reference numberISO 17850:2015(E)BS ISO 17850:2015ISO 17850:2015(E)ii
5、 ISO 2015 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2015, Published in SwitzerlandAll 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 o
6、n the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749
7、09 47copyrightiso.orgwww.iso.orgBS ISO 17850:2015ISO 17850:2015(E)Foreword ivIntroduction v1 Scope . 12 Normative references 13 Terms and definitions . 14 Measurement methods 24.1 General . 24.2 Local geometric distortion 34.3 Line geometric distortion 35 Requirements 45.1 Apparatus and hardware 45.
8、2 Lighting 45.3 Dot chart . 55.3.1 Design and characteristics. 55.3.2 Requirement for the chart planarity . 65.4 Grid chart . 75.4.1 Design and characteristics. 75.5 Image/camera settings 85.5.1 General 85.5.2 Basic settings and influencing factors . 85.5.3 Specific test procedures . 85.5.4 Position
9、ing of the camera . 85.5.5 Exposure, white balance, and focus . 96 Determination of geometric distortion .106.1 Local geometric distortion . 106.1.1 Numerical definition 106.1.2 Outline of the practical algorithm 106.2 Line geometric distortion . 116.2.1 Horizontal line distortion 116.2.2 Vertical l
10、ine distortion .126.2.3 Total line distortion 127 Presentation of results 137.1 General 137.2 Local geometric distortion . 137.3 Line geometric distortion . 14Annex A (informative) Illustrative example and validation 15Annex B (informative) Extracting the dots from the target .17Annex C (informative
11、) Dot centre validation 25Annex D (informative) Grid sort .30Annex E (informative) Example of subjective evaluation 40Bibliography .48 ISO 2015 All rights reserved iiiContents PageBS ISO 17850:2015ISO 17850:2015(E)ForewordISO (the International Organization for Standardization) is a worldwide federa
12、tion 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 committ
13、ee. 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.The procedures used to develop this document and t
14、hose 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 documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2
15、 (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 for identifying any or all such patent rights. Details of any patent rights identified during the development of the d
16、ocument 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 the convenience of users and does not constitute an endorsement.For an explanation on the meaning of ISO specific terms a
17、nd 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: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 42, Photography.iv ISO 2015 All
18、 rights reservedBS ISO 17850:2015ISO 17850:2015(E)IntroductionA digital still camera (DSC) typically employs a taking lens that is a rotationally symmetric optical system. Generally, the function of rotationally symmetric optical systems is to form an image that is geometrically similar to the objec
19、t except some particular systems, such as fish-eye lenses and eyepieces, where this condition is deliberately not maintained. This function is accomplished ideally according to the geometry of perspective projection. Departures from the ideal image geometry are called distortion. The distortion is a
20、 position-dependent quantity which generally has a vectorial character. In a given image plane (which may also lie at infinity), this vector, representing the difference between theoretical and real image position, has a radial and a tangential component. In optical systems, the tangential component
21、 is basically conditioned by imperfect rotational symmetry. The systems manufactured in accordance with the present state of the art have a negligible tangential distortion.Geometric distortion (GD) of DSCs is mainly caused by the variation of magnification in the image field of the camera lens. The
22、 most well-known effect of distortion is that straight lines appear curved. Generally speaking, the proportions between objects are not preserved in a distorted image, which can be very unpleasant for some natural scenes, architecture, or portraits. Distortion is fully described by a 2D map, giving
23、the displacement from a point in an ideal undistorted image to the point in the actual distorted image. The image centre is usually assumed to be undistorted; the magnification factor at this position actually defines the focal distance.Different types of distortion are usually characterized by how
24、the magnification radially varies within the image field. Barrel and pincushion are the most usual types of distortion for which magnification is respectively monotonously decreasing and monotonously increasing when moving along from the centre to the border of the image field. Other types which can
25、not be categorized into above two types are usually called wave distortion.a) Barrel (or negative) distortionb) Pincushion (or positive) distortionNOTE The magnification is decreasing for barrel distortion and increasing for pincushion.Figure 1 Two main types of distortions ISO 2015 All rights reser
26、ved vBS ISO 17850:2015ISO 17850:2015(E)ISO 9039 defines methods to measure a lens that is separated from a camera. On the other hand, this International Standard was developed and defines methods to measure the total image distortion of a camera including a lens and signal processing.This Internatio
27、nal Standard is based on both Reference 3 prepared by the Camera Phone Image Quality (CPIQ) group within the International Imaging Industry Association (I3A) and Reference 4 prepared by Camera and Imaging Products Association (CIPA).vi ISO 2015 All rights reservedBS ISO 17850:2015INTERNATIONAL STAND
28、ARD ISO 17850:2015(E)Photography Digital cameras Geometric distortion (GD) measurements1 ScopeThis International Standard specifies a protocol to measure geometric distortion of a digital camera. It is applicable to the measurement of digital cameras including camera phones.2 Normative referencesThe
29、 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 (including any amendments) applies.ISO 14524,
30、Photography Electronic still-picture cameras Methods for measuring opto-electronic conversion functions (OECFs).IEC 61146-1, Video cameras (PAL/SECAM/NTSC) Methods of measurement Part 1: Non-broadcast single-sensor camerasEBU Tech3249, Measurement and analysis of the performance of film and televisi
31、on camera lenses3 Terms and definitions3.1geometric distortionGDdisplacement from the ideal shape of a subject (lying on a plane parallel to the image plane) in the recorded imageNote 1 to entry: Geometric distortion basically derives from variation of lateral magnification in the image field of a c
32、amera lens and results in straight lines being rendered as curves. There are other factors to induce geometric distortion, for example, rotational asymmetricity of a camera lens or position shift processing in a camera imaging process.3.2image height3.2.1image heightdistance between an image point a
33、nd the centre of the image area or its relative expression which is the value normalized by one half of the diagonal of the image areaNote 1 to entry: This is an extension of the definition in ISO 9039 which is a measurement for optical systems.3.2.2actual image height image height of an actual reco
34、rded image point in the recorded image areaNote 1 to entry: “Actual recorded image point” corresponds to “observed image point” in ISO 9039.Note 2 to entry: “Image height” in ISO 9039 basically means “actual image height” but the usage is sometimes confusing. ISO 2015 All rights reserved 1BS ISO 178
35、50:2015ISO 17850:2015(E)Note 3 to entry: The adjective “actual” is used in similar meaning, “actual point” and “actual position”, for example.3.2.3ideal image heightimage height of a theoretical corresponding point in the recorded image area, assuming a geometrically undistorted image formationNote
36、1 to entry: This is an extension of the definition in ISO 9039 which is a measurement for optical systems.Note 2 to entry: The adjective “ideal” is used in similar meaning, “ideal point” and “ideal position”, for example.3.3image qualityimpression of the overall merit or excellence of an image, as p
37、erceived by an observer neither associated with the act of photography nor closely involved with the subject matter depictedNote 1 to entry: The purpose of defining image quality in terms of third-party (uninvolved) observers is to eliminate sources of variability that arise from more idiosyncratic
38、aspects of image perception and pertain to attributes outside the control of imaging system designers.3.4noiseunwanted variations in the response of an imaging system3.5resolutionmeasure of the ability of a digital image capture system or a component of a digital image capture system to distinguish
39、picture detail3.6TV distortionline distortion measured by conventional method of TV field defined in IEC 61146-1 (24 Geometric distortions) or EBU Tech3249 (2.11. Picture height distortion)4 Measurement methods4.1 GeneralAs defined in 3.1, geometric distortion basically derives from the variation of
40、 magnification in the image field. If this phenomenon occurs in an image, it means that a regular structure in an object does not appear to be regular in the image taken with the camera. There are two ways defined in this International Standard to quantify the amount of geometric distortion in an im
41、age. Both have their pros and cons.2 ISO 2015 All rights reservedBS ISO 17850:2015ISO 17850:2015(E)Figure 2 Regular grid (solid lines) in the scene is distorted and the red diamonds mark the position of the intersections in the image produced by the camera4.2 Local geometric distortionGeometric dist
42、ortion can be measured on a white chart containing black dots at the position of a regular grid or on a grid chart formed by straight lines. The local geometric distortion method analyses the grid formed by the test chart in the centre of the image and calculates the ideal positions of the structure
43、 based on the measured distances. After that, it analyses the rest of the image and locates all actual positions of the grid. The distance between the ideal position and the actual position is the geometric distortion at that location in the image.The distance between the two positions can be plotte
44、d as a function over the distance to the image centre. This curve indicates the variation of image magnification versus the actual image height, which is an expression of the geometric distortion called local geometric distortion. In order to limit the result to a single value that might get reporte
45、d with the cameras specifications, the maximum (peak to peak) value shall be reported.The manufacturing tolerances, such as lens tilt or off-centring, can result in a non-rotationally symmetric GD behaviour. If the system is not rotationally symmetric, it can lead to increased distortion levels in t
46、he image corners. In this case, the measured geometric distortion is correct for the camera under test but might not represent a standard camera of the tested model.4.3 Line geometric distortionThe principle of line geometric distortion is to measure the bending of a straight horizontal or vertical
47、line at defined distances from the image centre and to report the maximum of the measured bending. This bending is preferably measured on a chart with a regular line grid. ISO 2015 All rights reserved 3BS ISO 17850:2015ISO 17850:2015(E)Line geometric distortion is the direct measured result of this
48、method and it is easy to understand intuitively for consumers. However, it can also be interpreted from the measured result using the local geometric distortion method.NOTE The line geometric distortion has a long history and it has been used in the video technology for decades. The reason is that i
49、t was easy to determine this value with standard measurement equipment used in the analogue video world. The fundamental concept of this method was first standardized by the IEC in IEC 611461 in 1994.5 Requirements5.1 Apparatus and hardwareThe following hardware is necessary to control and report the test conditions: dot target or a grid chart; two light sources; device to measure the chart height captured in the image; mirror (for camera alignment with the target).5.2 LightingLighting uniformity is recommended to ease
