IEC TR 62977 3 2 Edition 1 0 201 6 01 TECHNICAL REPORT Electronic display devices – Part 3 2 Evaluation of optical characteristics – Mura IE C T R 6 2 9 7 7 3 2 2 0 1 6 0 1 (e n ) ® colour inside Inte[.]
I E C TR 62 7 -3 -2 ® Edition 201 6-01 TE C H N I C AL RE P ORT colour i n sid e E l ectron i c d i s pl a y d e vi ces – IEC TR 62977-3-2:201 6-01 (en) P art -2 : E val u ati on of opti cal ch aracteri s ti cs – M u I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n T H I S P U B L I C AT I O N I S C O P YRI G H T P RO T E C T E D C o p yri g h t © I E C , G e n e v a , S wi tz e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about I EC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local I EC member National Committee for further information IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab ou t th e I E C The I nternational Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes I nternational Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca ti o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal og u e - webstore i ec ch /catal og u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s s earch - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectroped i a org The world's leading online dictionary of electronic and electrical terms containing 20 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l os sary - s td i ec ch /g l oss ary 65 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i s h ed - webstore i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I E C C u stom er S ervi ce C en tre - webstore i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C TR 62 7 -3 -2 ® Edition 201 6-01 TE C H N I C AL RE P ORT colour i n sid e E l ectron i c d i s pl a y d e vi ces – P art -2 : E val u ati on of opti cal ch aracteri s ti cs – M u INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 31 20; 31 260 ISBN 978-2-8322-31 8-0 Warn i n g ! M ake su re th a t you obtai n ed th i s pu bl i cati on from an au th ori zed d i s tri bu tor ® Registered trademark of the International Electrotechnical Commission I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n –2– I EC TR 62977-3-2: 201 © I EC 201 CONTENTS FOREWORD I NTRODUCTI ON Scope Norm ative references Terms and definitions Standard m easuring conditions Standard measuring conditions Standard m easuring environm ental conditions Standard m easuring darkroom conditions Light m easuring device (LMD) Measuring setup 4 Test signal Measuring conditions Standard evaluation m ethod Measurem ent data processing method Measurem ent data processing flow General 2 Median filter process 1 Transform ation to opponent colour space from CI E XYZ Convolution with the contrast sensitivity function (CSF) of the hum an visual system 5 Transform ation to CI E XYZ from the opponent colour space Transform ation to CI ELAB from CI E XYZ a* correction Mura evaluation method General Lightness m ura evaluation 3 Chrom a m ura evaluation 5 Mura evaluation 5 Measurement report 6 Actual example General Evaluation obj ects Subj ective evaluation Evaluation by the m ethod indicated inthis docum ent using apparatus Correlation between subj ective evaluation and mura evaluation value Annex A (inform ative) S-CI ELAB m odel 20 A General 20 A S-CI ELAB m odel 20 A Spatial sensitivity function model (two-dimensional CSF m odel) 20 Annex B (inform ative) Type of m ura 24 B General 24 B Classification of mura 24 Annex C (informative) U se case of a m ura evaluation value 26 C General 26 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62977-3-2: 201 © I EC 201 –3– C Example of a use case of a m ura evaluation value 26 Annex D (informative) Various mura m easurement m ethods 27 D General 27 D Comparison of mura evaluation standards 27 Bibliograph y 28 Figure – Measuring layout Figure – Exam ple of input signal Figure – Measurement data processing flow adopting the S-CI ELAB model 1 Figure – Concept diagram of real-space inform ation integration Figure – × neighbourhood domain Figure – Evaluation obj ects in a dark room Figure – CSF filter images in opponent colour space Figure – Correlation of mura evaluation value and I TU -R subj ective evaluation values Figure A – Flowchart of S-CI ELAB calculation 20 Figure A – Two-dimensional CSF m odel 21 Figure A – Exam ples of the convolution of a two-dimensional CSF filter for illusion 23 Figure B – Classification of mura by form s and/or causes 25 Table Table Table Table Table Table Table Table Table – Exam ple of reported criteria of two-dim ensional LMD – Exam ple of measurement results for a display screen uniformity – I TU-R quality and im pairment scales – Subj ective evaluation results – Evaluation results by apparatus A – Parameters for each axis of the opponent colour space 21 C – Exam ple of a use case of a mura evaluation value 26 C – Exam ple of subj ects to evaluate 26 D – Comparison chart of various mura m easurem ent standards 27 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n –4– I EC TR 62977-3-2: 201 © I EC 201 INTERNATI ONAL ELECTROTECHNI CAL COMMISSI ON E L E C T RO N I C D I S P L AY D E VI C E S – P a rt -2 : E va l u a ti o n o f o p ti c a l c h a c te ri s ti c s – M u FOREWORD ) The I nternati on al Electrotechni cal Comm ission (I EC) is a worl d wid e organization for stan dardization com prisin g all n ation al el ectrotechnical comm ittees (I EC National Comm ittees) The object of I EC is to prom ote internati onal co-operation on all questions concerni ng stand ardi zati on in the el ectrical an d electronic fields To this end and in additi on to other acti vities, I EC publish es I nternational Stan dards, Techn ical Specifications, Technical Reports, Publicl y Avail abl e Specificati ons (PAS) an d Gu ides (h ereafter referred to as “I EC Publication(s)”) Thei r preparation is entrusted to technical comm ittees; any I EC National Comm ittee interested in the subj ect dealt with m ay partici pate in this preparatory work I nternational, governm ental an d n on governm ental organ izations l iaising with th e I EC also participate i n this preparation I EC collaborates closel y with the I ntern ational Organi zation for Stand ardization (I SO) in accordance with ditions determ ined by agreem ent between th e two organi zati ons 2) The form al decisions or ag reem ents of I EC on tech nical m atters express, as n early as possible, an i nternati onal consensus of opi nion on the rel evant subjects since each technical com m ittee has representati on from all interested I EC N ational Com m ittees 3) I EC Publications have the form of recomm endations for intern ational use an d are accepted by I EC National Com m ittees in that sense While all reasonable efforts are m ade to ensure that the tech nical content of I EC Publications is accu rate, I EC cann ot be h eld responsi ble for th e way in which th ey are used or for an y m isinterpretation by an y en d u ser 4) I n order to prom ote intern ational u niform ity, I EC National Com m ittees und ertake to apply I EC Publications transparentl y to the m axim um extent possible i n their national an d regi on al publicati ons Any d ivergence between an y I EC Publication and the correspondi ng national or regi on al publicati on sh all be clearl y in dicated in the latter 5) I EC itself d oes n ot provi de an y attestation of conform ity I n depend ent certificati on bodies provi de conform ity assessm ent services and, in som e areas, access to I EC m arks of conform ity I EC is not responsi ble for any services carri ed out by ind ependent certification bodi es 6) All users shou ld ensure that th ey have the l atest editi on of thi s publicati on 7) No liability shall attach to I EC or its directors, em ployees, servants or ag ents inclu din g in divi dual experts an d m em bers of its technical com m ittees and I EC Nati on al Com m ittees for any person al i njury, property d am age or other dam age of any n ature whatsoever, wheth er di rect or indirect, or for costs (includ i ng leg al fees) and expenses arisi ng out of the publ ication, use of, or relian ce upon, this I EC Publicati on or any other I EC Publications 8) Attention is drawn to th e N orm ative references cited in th is publ ication Use of the referenced publ ications is indispensable for the correct applicati on of this publication The m ain task of I EC technical comm ittees is to prepare I nternational Standards H owever, a technical committee m ay propose the publication of a technical report when it has collected data of a different kind from that which is normally published as an I nternational Standard, for exam ple "state of the art" I EC TR 62977-3-2, which is a technical report, has been prepared by I EC technical committee 1 0: Electronic display devices The text of this technical report is based on the following documents: Enqui ry draft Report on votin g 1 0/674A/DTR 1 0/701 A/RVC Full information on the voting for the approval of this technical report can be found in th e report on voting indicated in the above table This publication has been drafted in accordance with the I SO/I EC Directives, Part I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62977-3-2: 201 © I EC 201 –5– A list of all parts in the I EC 62977 series, published under the general title Electronic display devices , can be found on the I EC website The committee has decided that the contents of this publication will rem ain unchanged until the stability date indicated on the I EC website under "http: //webstore.iec ch" in the data related to the specific publication At this date, the publication will be • • • • reconfirmed, withdrawn, replaced by a revised edition, or amended A bilingual version of this publication may be issued at a later date I M P O RT AN T – T h e ' c o l o u r i n s i d e ' th at it tai n s u n d e rs t a n d i n g c o l o u r p ri n t e r I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n of c o l o u rs i ts wh i c h c o n te n ts l og o a re U s e rs on th e co ve r p ag e o f th i s c o n s i d e re d s h ou l d to t h e re fo re be p u b l i c ati o n u s e fu l p ri n t th i s fo r i n d i c ate s th e d o cu m en t c o rre c t u si n g a –6– I EC TR 62977-3-2: 201 © I EC 201 INTRODUCTION Electronic displays, for example liquid crystal displays (LCDs), plasm a display panels (PDPs), organic light em ission displays (OLEDs), and so on, have grown popular as displays for highquality im ages I t is therefore increasingl y important to measure the image quality of electronic displays One factor degrading the image quality is non -uniform ity, known as ‘m ura’ The m ura is classified into three types The first is lum inance m ura, the second is colour m ura The third is called merel y “m ura” and includes luminance m ura and colour m ura sim ultaneousl y I t is im possible to recognize lum inance mura and colour m ura as completel y separate objects Various m easurement methods about lum inance m ura and colour mura have been reported in various academic conferences There are also some standards for these mura For example, uniform ity of lum inance and chrom aticity are specified in I EC I EC 61 747-30-1 , SEMU (SEMI m ura) is specified in SEMI D31 -021 and uniform ity m easurem ent is specified in I DM S ver 03 sec H owever there is no report which clearl y provides the quantitati ve m ethod for the mura that is called merel y “m ura” (see Annex D) Therefore the majority of electronic display m anufacturers are still using the lim it sam ple for visual inspection This Technical Report, which intends to verify one mura m easurem ent method, shows the detailed mura m easurement m ethod and its inspection experim ent results The I nternational Electrotechnical Comm ission (I EC) draws attention to the fact that it is claimed that com pliance with this docum ent may involve the use of a patent I EC takes no position concerning the evidence, validity and scope of this patent right The holder of this patent right has assured the I EC that he/she is willing to negotiate licences either free of charge or under reasonable and non-discriminatory term s and conditions with applicants throughout the world I n this respect, the statement of the holder of this patent right is registered with I EC I nform ation may be obtained from: Son y Corporation -7-1 Konan, M inato-ku, Tokyo, 08-0075 J apan Attention is drawn to the possibility that som e of the elem ents of this docum ent may be the subj ect of patent rights other than those identified above I EC shall not be held responsible for identifying an y or all such patent rights ISO (www iso org/patents) and I EC (http: //patents.iec.ch) maintain on-line database of patents relevant to their standards Users are encouraged to consult the databases for the most up to date inform ation concerning patents I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62977-3-2: 201 © I EC 201 –7– E L E C T RO N I C D I S P L AY D E VI C E S – P a rt -2 : E va l u a ti o n o f o p ti c a l c h a c te ri s ti c s – M u S cop e This part of I EC 62977, which is a Technical Report, provides an optical m easuring m ethod of mura for electronic displays I t defines general m easuring procedures for m ura measurem ent and an evaluation method of electronic displays N o rm a t i ve re fe re n c e s The following docum ents, in whole or in part, are referenced in this docum ent 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 an y amendments) applies Void T e rm s a n d d e fi n i t i o n s For the purposes of this docum ent, the following terms and definitions apply l i g h t n e s s m u lum inance unevenness whose lightness differs partiall y from the background lightness of a display screen with the exception of pixel defects c h ro m a m u colour unevenness whose chroma differs partially from the background of a display screen with the exception of pixel defects 3 m u both luminance and colour unevenness whose lightness and chrom a differ partiall y from the background of a display screen with the exception of pixel defects Note to entry: I n gen eral, lightn ess m ura and chrom a mura exist sim ultaneousl y Mu eval uati on shows the deg ree of screen un iform ity considerin g how both lig htness mura and ch rom a m ura affect hu m an percepti on l i g h t n e s s e d g e a re a ratio of lightness gradient area that is rapidl y changed lightness to whole screen area l i g h t n e s s m u a re a area of uneven lightness that is bright or dark regions against the background of a display screen m a xi m u m l i g h t n e s s d i ffe re n c e maximum lightness difference from the average L * of a whole display screen I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n –8– I EC TR 62977-3-2: 201 © I EC 201 ch rom a ed g e area ratio of the chroma gradient area that is rapidly changed from the chroma to the whole screen area ch rom a m u area area of uneven chrom a that is coloured regions against the background of a display screen maxi m u m ch rom a maximum C* value in a whole display screen oppon en t col ou r space three dimensions that are described as w/k, r/g, and b/y channels Note to entry: The w/k ch ann el is a l um inance com ponent Th e r/g and b/y chan n els are a ch rom aticity com ponent of red to green, blu e to yellow, respectively Stand ard measuri ng condi ti on s Stan d ard m easu ri n g d i ti on s Stan d ard m easu ri n g en vi ron m en tal d i ti on s The standard measuring environmental conditions specified in IEC 62341 -6-1 :2009, 5.1 , should be applied [1 ] Stan d ard m easu ri n g d arkroom d i ti on s The standard measuring darkroom conditions specified in I EC 62341 -6-1 : 2009, 2, should be applied [1 ] Li g h t m easu ri n g d evi ce (LM D) The LMD used for m easurements of the displays should be checked for the following criteria and specified accordingly: • • • • • • sensitivity of the m easured quantity; errors caused by veiling glare and lens flare (i e stray light in optical system); errors caused by camera noise (i e dark charge noise of a charge coupled device (CCD)); timing of data-acquisition and aliasing-effects; linearity of detection and data conversion; resolution when using a two-dim ensional LMD A two-dimensional LMD such as a CCD area detector should be used for these m easurements When using a two-dim ensional LMD, it should be calibrated, so that the measurem ent results correspond to those by the point-m easurement LMD A two-dimensional LMD measures a map of lum inance and/or colour coordinate values over the m easurement area of the screen The specification of the LMD used should be noted in the report as shown in Table for exam ple _ Num bers in sq uare brackets refer to the Bi bliography I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 16 – 5.3.3.3 I EC TR 62977-3-2: 201 © I EC 201 Chroma mura area The chroma m ura area is com puted as the pixel count ratio of the area whose chroma value is more than on a display screen to the pixel count of the whole screen area 5.3.3.4 M aximum chroma The m aximum C* value in the whole display screen is defined as m axim um chrom a 5.3.4 M ura evaluation The purpose of this m easurem ent is to evaluate the m ura of the display screen Formula (1 5), described in detail in [6], should be applied to com pute a m ura evaluation value (1 5) MEV = 0, 705 LEV + 0, 634 CEV where MEV is the m ura evaluation value 5.3.5 M easu rement report The m easured result should be reported in a table Table shows an example Table – Example of measurement resu lts for a display screen uniformity Measuri ng item Evalu ation valu e Signal l evel 50 % of full white Mu evalu ation val ue 3, 80 Classification of m ura (see An nex B) Fram e m ura Lightness m ura evalu ation valu e 3, 61 Chrom a m ura evaluati on val ue , 98 M ura evaluation index Value of index Lightness m ura area 0, 671 M ura image Bright area Maxim um lightness difference 3, 01 Lightness edg e area 0, 089 Chrom a m ura area 0, 31 Maxim um chrom a 5, 65 Chrom a edg e area 0, 051 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n Dark area I EC TR 62977-3-2: 201 © I EC 201 6 – 17 – Ac t u a l e xa m p l e G e n e l The following is an actual exam ple of m ura evaluation values com puted with the above measurement method and of the correlation of these values and subjective evaluation values All the data in Clause is reported in [8] E va l u a ti o n o b j e cts The evaluation objects were three comm ercially available 55-inch TVs and one 25-inch professional m aster m onitor installed in a dark room as shown in Figure Three input signal levels (1 00 %, 50 % and 20 % of full white described in 4) were used Therefore, the evaluation subjects included conditions IEC F i g u re – E v a l u a t i o n o b j e cts i n a d a rk ro o m S u b j ecti ve eval u ati on A subj ective evaluation was conducted using the five-grade impairm ent scale based on [1 3] and shown in Table The visual inspection criteria colum n in Table shows the criteria that are generall y used by a manufacturer inspector These criteria should be noted because they are affected by the application of the displays: com mercial m odel TVs, PC monitors, broadcast reference m onitors, medical m onitors and so on (see Annex C) I n this experiment, participants were instructed to evaluate a commercial model TV There is one more point to be careful about when perform ing a subj ective evaluation Because it is impossible to recognize lightness m ura and chrom a m ura as com pletel y separated objects, the subjective evaluation value corresponds to MEV (m ura evaluation value) There were participants who evaluated the degree of mura by watching each display screen at a distance of three times the display height from the display screen T a b l e – I T U -R q u a l i t y a n d G d e Qu al i t y Excellent i m p a i rm e n t s c a l e s I m p a i rm e n t Vi s u a l i n s p e c ti o n c ri t e ri a I m perceptibl e Al m ost no effect Good Percepti ble, but not ann oyi ng Can be seen, but no effect on the custom er Fair Slightl y an noyin g Acceptable l evel Poor Annoyin g Can be seen, an d not an acceptable l evel Bad Very an noyin g Very bad I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 18 – I EC TR 62977-3-2: 201 © I EC 201 The results of the subj ective evaluation are shown in Table The bottom row in Table shows the average value of each stimulus to compare with the m ura evaluation value Table – Su bjective evaluation results Signal level 55-in ch 55-in ch 55-in ch 25-in ch TV no TV no TV no M aster monitor 20 50 00 20 50 00 20 50 00 20 50 00 A 3 2, 4 4, 5 5 B ,5 3 4 4 5 5 C 2 3 4 5 5 D 2 4 E 2, 2, 2, 2, 3, 4, 4, 4, 4, F 3 2, 2, 3 4 5 G 3, 3, 4, 5 4, 5 5 H ,5 3 4 4 5 Average ,5 2,8 2,7 2, 3, 3,7 3, 4,5 4,7 4,9 4,7 (%) NOTE The l etters A to H in dicate each participant 6.4 Evaluation by the method indicated inthis document using apparatus According to Clause 4, the m easurem ent with the apparatus was perform ed A 2D colorimeter was used to obtain an XYZ 2D distribution data of conditions which were sam e as the subj ective evaluation in the dark room The evaluation was performed according to Clause To calculate MEV, an anal ysis software that implem ented this evaluation method was prepared Figure shows the example of CSF filter im ages for each axis of the opponent colour space com puted based on Annex A A CSF filter set should be computed for each measurement image, based upon display size, viewing distance, and m easured XYZ image (a) CSF for w/k (b) CSF for r/g (c) CSF for b/y IEC Figure – CSF filter images in opponent colou r space The evaluation results are shown in Table The comparison with the subjective evaluation value is im possible for lightness mura and chroma m ura, but the evaluation values for these are listed for reference I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62977-3-2: 201 © I EC 201 – 19 – T a b l e – E va l u ati o n Signal l evel (% ) re s u l t s b y a p p a t u s 5 -i n c h 5 -i n c h TV n o TV n o 5 -i n c h TV n o -i n c h M a s te r m o n i to r 20 50 00 20 50 00 20 50 00 20 50 00 5, 6, 6, 0, 5, 3, 4, 2,8 ,5 ,6 ,3 ,1 Lightness mura evaluation value 13 4, 4, 9, 4, 3, 2, 1 ,6 0, 0, 0, 0, Chroma mura evaluation value 9, 4, 5, ,5 ,6 4, 2, ,8 ,8 ,5 ,5 MEV (mura evaluation value) C o rre l a t i o n b e twe e n s u b j e cti ve eval u ati o n an d m u e v a l u a t i o n val u e Mura evalu ation val ue The correlation between the subj ective evaluation value (in Table 4) and the m ura evaluation value (in Table 5) is shown in Figure The results show a high correlation ( R = 0, 90) These results lead to the conclusion that a visual inspection can be replaced with the m ura m easurement m ethod described in this document 18 16 R = 0, 90 14 12 10 0 I TU-R su bjecti ve evaluati on g rade IEC F i g u re – C o rre l a t i o n o f m u e v a l u a t i o n I T U -R s u b j e ct i ve e v a l u a ti o n I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n val u e an d val u e s – 20 – I EC TR 62977-3-2: 201 © I EC 201 An n e x A (informative) S -C I E L AB m o d e l A G e n e l A screen im age is perceived through human eyes Therefore, it is im portant to consider the characteristics of the hum an visual system for the evaluation The spatial contrast sensitivity function is one of the useful characteristics for the evaluation of screen image quality The CSF (contrast sensitivity function) is defined as the relationship between the spatial frequency and the contrast sensitivity of a hum an visual system I n this docum ent, the CSF of the human visual system is introduced for m easurement data processing to match the evaluation result to the hum an perception A S - C I E L AB m o d e l The S-CI ELAB model was proposed for the measurem ent of the colour reproduction error in digital im age by Zhang and Wandell in 997 [9] Figure A shows how to calculate the SCI ELAB representation The image data is transform ed into an opponent colour space Each opponent colour im age is convolved with a kernel whose shape is determined by the visual spatial sensitivity to that colour dimension The filtered representation is transform ed into a CI E XYZ representation, and this representation is transform ed using the CI ELAB form ulae Color im age Color separation Lum R/G B/Y Spatial filter XYZ S-CI ELAB F i g u re A A IEC – F l o w c h a rt o f S - C I E L AB c a l c u l a t i o n S p a t i a l s e n s i t i vi t y fu n c t i o n m o d e l ( tw o -d i m e n s i o n a l C S F m o d e l ) The dependence of directivity in the spatial frequency characteristics of the human eye was measured The result shows the anisotropic properties of contrast sensitivities in spatial frequency The contrast sensitivity of the vertical and horizontal directions is superior to that of the diagonal direction (see Figure A 2) Based on this result, a two-dim ensional CSF model I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62977-3-2: 201 © I EC 201 – 21 – of the hum an eye was proposed by Mi yake [1 0], [1 ], [1 2] I t is therefore this two-dim ensional CSF model of the human eye considered with anisotropic properties which is intended to reflect more accurate characteristics of the hum an visual system for the evaluation NOTE I n references [9] to [1 2], the authors have used the word “MTF (m odul ation transfer function) of the eye” instead of “CSF” To avoid an y confusion, “CSF” is used to represent the spatial freq uency characteristics of the hum an eye L*c*h* W/K Origi nal I m age distortion m ap ΔE94 R/G L*c*h* Com pared B/Y IEC NOTE ∆E94 is a colour difference d efined in CI E 1 -1 994 [1 4] Figure A.2 – Two-dimensional CSF model The dependence of directivity in the two-dimensional CSF model of the human eye is calculated with the following formula specified in [1 0] and given in more detail in [1 2] Meye ( u , v ) = M0 ( ω )[1 – {1 – γ ( ω )} |sin (2 φ )| ] (A.1 ) where ω = ( u + v ) /2 φ = tan -1 ( u /v) ( u , v) is the spatial frequency coordinate in (cycle per degree) M0 ( ω ) is the spatial frequency characteristics of the horizontal direction M0 ( ω ) = β( O ) ⋅ exp{-2 π ⋅ σp ⋅ ( ω – m p ) } ε ⋅ [ β( O) ⋅ exp{-2 π ⋅ σp ⋅ ( m c – m p ) } – b ias ] ⋅ exp{-2 π ⋅ σc ⋅ ( ω – m c ) } (A.2) (A.3) NOTE M0 ( ω ) is expressed for each opponent col ou r space using different param eters (see Tabl e A ) Table A.1 – Parameters for each axis of the opponent colour space Opponent colou r space w/k r/ g b /y β( O ) βw( wk ) βr ( rg ) βb ( b y ) γ(ω ) γ w( ω ) γr( ω ) γb ( ω ) mp σp ε mc σc b i as 5, /40 1 /1 55 ,5 /70 NA NA NA ,5 /45 /4 7, /20 NOTE For th e colour space of r/ g, “ m c ”, “ σc ” an d “ b i as ” are not defined since ε =0 I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 22 – I EC TR 62977-3-2: 201 © I EC 201 β( O ) is the maximum sensitivity coefficient defined in each opponent colour space The values of w k , rg and b y are the average of each value of the opponent colour space in the whole display screen βw( wk ) = 0,003 626 wk – 0,428 34 w k + 7, 342 w k – 50, 764 βr( rg ) = -0,075 70 rg + 8, 731 rg – , 839 βb ( b y) = 0, 000 777 26 b y – 0, 099 832 b y2 + 5,090 b y + ,3 (A.4) γ ( ω ) is the correction factor of the spatial frequency characteristics of the 45° direction γ ( ω ) is expressed by a different form ula for each opponent colour space: γ w( ω ) γ r( ω ) γb ( ω ) = 0,003 00 ω – 0, 06 80 ω + , 396; = 0,001 531 ω – 0, 061 49 ω + , 40; = 0, 001 91 ω – 0, 064 27 ω + , 090 (A.5) Therefore, Meye ( u , v ) is calculated for each opponent colour space as shown in Figure Each of the opponent colour data was convolved with the visual spatial sensitivity function calculated using formulae (A ) to (A 5) I t is necessary to match a unit of the visual spatial sensitivity function filter to that of the Fourier transform ed data Because the m easured im age data does not have a unit such as length and angle on real space, the unit of the Fourier transform ed data is “cycle per CCD pixel” To make the Fourier transform ed data have the sam e unit as the CSF filter, “ GF ” is a useful factor to transform the unit (see 3.2 2) GF = HR × × VD × tan (0, 5) / WL [CCD pixel/degree] (A.6) where GF HR VD WL is the geom etric factor relating the m easured screen im age with the real-space inform ation is the horizontal pixel num ber of the measured screen im age (CCD pixel) is the viewing distance (in m m) is wide length of Display screen (in mm) The two-dim ensional CSF m odel of the human eye is one of the useful characteristics for converting a m easured image with an apparatus to a recognized im age by the hum an visual system Figure A.3 shows two examples These examples show that some visual illusion is computable by adapting the two-dimensional CSF filters I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62977-3-2: 201 © I EC 201 “Mach effect” – 23 – “Harman grid effect” Horizontal profile Origi nal im age Origi nal im age CSF filtered im age Horizontal profile CSF filtered im age Horizontal profile IEC Figure A.3 – Examples of the convolution of a two-dimensional CSF filter for illu sion I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 24 – I EC TR 62977-3-2: 201 © I EC 201 Annex B (informative) Type of mura B.1 General Mura could be classified depending on its form and/or causes I t is useful to classify m ura for defect anal ysis Various types of m ura classification , including a specific cause for LCDs, were shown by Mr Kai Chieh Chang in the m eeting of I EC TC 1 in 2009 The classification of m ura is shown in Clause B.2 B.2 Classification of mura The classification of m ura by form s and/or causes, including a cause peculiar to LCDs, is shown in Figure B Classification Appearance Classification Bright spot White spot Spacer cluster Bl ack spot Dark spot V-line Backlight white spot H-li ne Backlight dust black spot Rubbin g m ura Polari zer white spot Backlight scratch I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n Appearance I EC TR 62977-3-2: 201 © I EC 201 Classification Appearance – 25 – Classification Polari zer black / white spot Polari zer scratch Cell dust white spot Backl ight leakage H-ban d Fil l port m ura V-band CF m ura File wavi ng Gap m ura Shot m ura Bubbl e m ura Fram e m ura Gravity m ura Cell light leakag e V-line cl uster Arou nd m ura Clou d m ura Classification Appearance Classification Appearance Appearance Butterfl y m ura IEC Figure B.1 – Classification of mura by forms and/or causes I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 26 – I EC TR 62977-3-2: 201 © I EC 201 An n e x C (informative) U s e c a s e o f a m u e va l u a ti o n va l u e C G e n e l The I TU-R five-grade im pairm ent scale is well known as a method for subjective assessm ent of image quality The I TU-R five-grade visual inspection class is often used for m ura evaluation Therefore, knowing the relation between the m ura evaluation value and the I TU-R five-grade visual inspection class is useful for the assessm ent of a m ura quality level C E xa m p l e o f a u s e c a s e o f a m u e va l u a t i o n va l u e An example of a use case of a mura evaluation value is shown in Table C , and an example of subj ects to evaluate is shown in Table C Tabl e C – E xa m p l e o f a u s e c a s e o f a m u e v a l u a t i o n val u e I T U - R fi v e - c l a s s v i s u a l Cas e Cas e Case to to to to1 to to to to to to 20 to to 20 to 25 to to i n s p e c ti o n T a b l e C – E xa m p l e o f s u b j e c t s t o e v a l u a t e S u b j e c t ( d e vi c e ) S i g n al i n p u t l e ve l 20 % TV 50 % 00 % 20 % Monitor 50 % 00 % 20 % Monitor for m edical 50 % 00 % I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I EC TR 62977-3-2: 201 © I EC 201 – 27 – An n e x D (informative) Va ri o u s m u m e a s u re m e n t m e th o d s D G e n e l Various m easurement methods for luminance m ura and colour m ura have been used in various countries H owever, there are hardl y an y m ethods that can be suggested for standardization I n this docum ent, a m ura m easurement m ethod using a 2D colorim eter is introduced, with the exception of the legacy m ethod such as nine-point measurement D C o m p a ri s o n o f m u e va l u a t i o n s t a n d a rd s The comparison chart of a mura measurement m ethod using a 2D colorimeter is shown in Table D I n I DM S the contrast sensitivity function (CSF) is applied to the human visual system However, there are few descriptions of colour m ura such as the following, “Color nonuniformities can optionally be measured by appl yi ng an appropriate CSF to chrom aticity data and calculating the same defects.” [3] As in I DMS, SEMI D31 -021 does not support m ura, including luminance and colour m ura sim ultaneousl y The scope of SEMI D31 -021 is onl y about the luminance m ura [4] The threshold value is necessary to extract mura obj ects appl ying D31 -021 3, however, there is no description in the standard document of how to extract the m ura area Therefore the extract value cannot becom e common, because it is up to the user to define the threshold value The second column in Table D.1 is the method used in this docum ent I t is suitable to the human visual system and has a high accuracy and availability Tabl e D C o m p a ri s o n – C o m p a ri s o n i te m s Project/d ocum ent num ber c h a rt o f v a ri o u s m u m e a s u re m e n t s t a n d a rd s I E C TC 1 I CDM versi on 03 Sec 2: I EC TR 62977-3-2, Editi on I DMS AREA UNI FORMI TY SEM I SEMI D31 -021 Lightness m ura availabl e available available Chrom a m ura availabl e available not avail abl e Mu (lig htness and chrom a m ura exist sim ultaneously) availabl e not avail abl e not avail abl e supported supported not supported Helmholtz–Koh lrausch effect supported not supported not supported Display size factor supported lim ited not supported Viewin g distance factor supported lim ited supported Concept, comm on availabl e available available Accuracy with actual sam pl e availabl e not avail abl e not avail abl e Avail ability availabl e lim ited lim ited Human vision factor: Contrast spatial frequency Human vision factor: I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n – 28 – I EC TR 62977-3-2: 201 © I EC 201 Bibliography [1 ] I EC 62341 -6-1 :2009, Organic light emitting diode (OLED) displays – Part 6-1: Measuring methods of optical and electro-optical parameters [2] CI E Publication (2004), Colorimetry [3] I CDM I nformation Display Measurement Standard (I DM S) version 03: Sec and A4 [4] SEMI D31 -021 3, Definition of Measurement Index (Semu) for Luminance Mura in FPD [5] K N agamine, S.Tom ioka, T.Tamura, and Y Shimpuku, A Quantitative Evaluation Method for Color Uniformity of a Display Screen Based on Human Perceptions Proc 31 st I DRC EuroDisplay 201 : session [6] K N agamine, S.Tom ioka, T.Tam ura, and Y Shim puku, A Quantitative Evaluation Method for Luminance and Color Uniformity of a Display Screen Based on Human Perceptions I EI CE TRANS ELECTRON , Vol E95-C, No 1 N ov 201 2: p1 699-1 706 [7] K N agamine and S.Tom ioka, A Quantitative Mua Evaluation Method that Depends on Viewing Distance Proc th I nternational Display Workshops, Kyoto, 201 2: p1 9751 976 [8] S H asegawa, S.Tomioka and K Nagm ine, General FPD Mura Index under the IEC Measurement Standard Proc 21 th I nternational Display Workshops, N iigata, 201 4: p949-952 [9] X Zhang and B A.Wandell, A Spatila Extension of CIELAB for Digital Color Image Reproduction Journal of Society I nformation Display, 997 5(1 ): p61 -63 [1 0] Y Mi yake, T I shihara, K Ohishi, and N Tsumura, Measurement and Modeling for the Two Dimensional MTF of Human Eye and Its Application for Digital Color Reproduction Image Quality Inspection Proc I S&T and SI D N inth Color I m aging Conference, 2001 : p1 53-1 57 [1 ] Y M iyake and K Mi yata, Evaluation of multispectral imaging, COLOUR I MAGE SCI EN CE Exploiting Digital Media, 2002: p77-98 [1 2] T I shihara, K Ohishi, N Tsumura and Y Mi yake, Dependence of Directivity in Spatial Frequency Response of Human Eye J ournal of The Society of Photographic Science and Technolog y of J apan, Vol 65, N o 2, 2002: p1 21 -1 33 [1 3] Recommendation 500-1 3, “ Methodology for the Subjective Assessment of the Quality of Television Pictures”, I TU-R Recomm endations, 201 [1 4] CI E 1 4-1 994, CIE Collection in Photometry and Radiometry _ I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n INTERNATIONAL ELECTROTECHNICAL COMMISSI ON 3, rue de Varembé PO Box 31 CH-1 21 Geneva 20 Switzerland Tel: + 41 22 91 02 1 Fax: + 41 22 91 03 00 info@iec.ch www.iec.ch I n tern ati o n al E l ectro tech n i cal C o m m i s s i o n