EclairColor Rev11

EncodinganddisplayingHDRcontentforcinemaCÉDR I C L E J EUNE , V P O F T E CHNO LOGY & I NNOVAT ION -

Whitepaper,revision1,Feb2017

EclairColor Rev12

IntroductionTheEclairColorprojectinitsfirstphaseisaboutbringingHDRimagestoavastnumberoftheatersintheworld;webelievethataHDRtechnologymustfitallcinemas:allmovies,allscreens,atreasonablecostsoitcanbebroadlydeployed.

Fromacontentcreationperspective,itisnecessarytohaveawaytoeasilydelivermultipleformats-fortheaters,TV,OTTandmobile-ashighandstandarddynamicencodings.

SinceEclairprovidestheatricaldeliveryservices,itwouldbeunrealistictocreateDCPsthatarelargerthantheoneswedelivertotheatersviasatellite,broadbandorharddrives.Theamountoftimerequiredfordeliveryisshortereveryday,thereforeweneedtoworkontheencoding/decodingoftheimagestokeepthe size of the DCPs reasonable, while keeping the quality pristine. We also need to use the currenttransportinfrastructuresfordistribution.

To achieve these goals,weutilizeproven technologies that are currently available and thatprovideanaffordable, reliable and secure solution to the market: ACES color management and SMPTE DCP as acontainer.

HDRinthecinemaOriginally, Digital Cinema offered a much better performance of image characteristics than TV: thesequentialcontrastratioofaDLPprojectorcouldreach2000:1whileLCDTVswouldusuallystayunder800:1.

Today,TVmonitorsusetechnologiessuchasdynamicbacklightingofLCDdisplays,veryhighcontrastOLEDorQuantumDotsdisplaythatcanachieveveryhighcontrast,upto1.000.000:1,whiledisplayingDCI-P3primariesorevenRec2020.

Thenextgenerationofcinemas,asapremiumexperience,shouldmeetorexceedHDRTVperformances.Currently available projectors allows for contrast of more than 6000:1, with Dolby Cinema claiming1.000.000:1.Lasertechnologiesalsoallowsforuseofawidergamutofcolors.Theseparametershavetobeconsideredforafuture-prooftransportsystem.

StateoftheartAsforsignalencodinganddecoding,severaloptionsareavailableonthemarket:

DCIspecificationsFor image transport, digital cinema is using the specifications designed by theDigital Cinema Initiativeworkgroup. TheDCIworkgrouphas issued these specifications in2005before the SMPTE createdanddeveloped theassociated standards.Thesewere the resultsof compromises largelybasedon technicalperformancesandpracticesatthattime.

Theachievablecolorspacechosenislargerthantheoneusedbytelevisionatthattime,knownasRec709color gamut. This new color gamut is called P3 and is using Red Green and Blue primaries thanwereachievablethroughfilteringoftheXenonbasedlightingusedforcinemaprojection.

ThecodingprincipleisbasedonthetransmissionofcolorsintheuniversalXYZcolorspacedefinedbyCIEandbyapplyingatransferfunctioninordertotakeadvantageofthenon-linearcharacteristicofthehumanvisualperception.

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Thesignalisencodedwithaninversegammaof2.6,itisdecodedwithatransferfunctionthatisagammacurveof2.6.

Itisaprovensystemwithgreatresultsforstandarddigitalcinema,thoughitpresentssignificantlimitationsintoday’scontext:

• differenttechnologiescanhavesignificantlydifferentrenderingsofthesamesignal• InthecontextofHDR,sincemostoftheinformationsitsintheregulartonalrange,weneedmore

codesinthedarkluminancevalues• UsingX’Y’Z’encoding,whichisusefultodifferentiatecontentfromotherRGBencodedcontent,

butwastesalotofcodevalues.

ITUBT1886ITUBT1886wasdesignedtoprovidebetterconsistencyacrossTVmonitorrenderingwhileshowingSDRITURec709encodedcontent.Itprovidesawaytoconsidertheblacklevelperformanceofthemonitorandadaptitsrenderingtoit.

HybridLogGammaHLGhasbeendesignedbytheBBCandtheNHKwiththemainpurposeofcarryingHDRinformationinSDRinfrastructures.

SL-HDR1A proposition by ST Microelectronics, Philips, CableLabs and Technicolor, SL-HDR1 relies on dynamicmetadatatorebuildanHDRsignaloutofaSDRstream.

HDR10The HDR10 Media Profile uses the SMPTE 2084 Perceptual Quantizer curve developed by DolbyLaboratorieswhileusingRec2020colorspacewithaquantizationover10bits.

DolbyVisionDolbyVisionisusingasetofmetadataontopofHDR10toprovidemoredetailsandaddressanevenwiderdynamicrange.UsingICtCpcolorencodingit’scapableofgettingbetterencodingefficiencyoncompatiblesystems.

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EclairColorMasteringEclairColorcontentiscolorgradedwithanHDRapproach,whichmeansthatwekeepdiffusewhiteatalevelcomparabletotheregularcinemastandard(48nits)andleaveheadroomforextraimpactonspecularlights, finerdetails likehairand textures,andalsoallow formorevivid colorsas theycan reachhigherbrightness.Thepeakwhitepointissetto103nits(30footlamberts),thisvaluewaschosenaftertesting,forthebestcompromisebetweenpeakbrightnessandthequalityofblackinatypical“optimized”theaterenvironment. In purposely design theaters, better performance can be achieved for black level andreflectivity.

BlacklevelinSDRvsHDR

Contrastratiointheatricalenvironment

ItisalsoimportanttokeeptheoveralllookconsistentwiththeSDRversion.Cinematographersdon’twanttomake anothermovie, theywant to enhance details and get better emotional impact onwhat theyconsiderthemostimportantcomponentsintheimage,byusingmorerangefordetailsinthehighlights,thedarkareas,andbrightercolors. It isalso importanttoconsiderthathigheroverallbrightnessofthepicture can be problematic at 24 fps in a dark environment, showing stuttering effect.Using theACESworkflow,EclairColorisimplementedthroughanOutputDeviceTransform.

EclairColor Rev15

ThemostconvenientwayforthecreativeprocessistostartwiththeEclairColorversionandthenderivetheSDRversion.However,thisisnotalwayspossiblesowedevelopedaremasteringworkflowusedforcatalogmoviesandmoviescolorgradedinotherfacilities.Thisprocessisvalidatedbytheclienttomakesurewefullyrespectthecreativeintent.

SignalencodingInthecontextofEclairColor,wedecidedtocomplywithseveralconstraints:

• KeepingtheDCIinfrastructurefordeliveryandplaybackofcontent• Differentprojectortechnologies,withdifferentsequentialandintra-framecontrastratio• Potentialfordifferentmasteringcolorgamuts(Rec709toRec2020)• Apeakwhitevaluesetat103nitstoallowforheadroomwhilekeepingareasonableblackvalue• Higherbrightnessmeaningmoreinteractionwiththeroom(reflectivity)• TheatersoptimizedforHDR,butnotnecessarilybuiltonpurpose

WedecidedtousetheSMPTEDCPandJPEG2000encoding,arobustplatformforsecurityandquality,aswellasformetadatasupport.

Wechosegammaencoding,whichhasprovenanefficientwaytoencodetheimageintheuseddynamicrange.Thevalueof2.8givessufficientcodesinthedarkareaswhilekeepingthediffusewhiteaboutthesamevalueaswhiteinDCI(48nits),whichisacreativechoice.

Measurementcontraststepsinthetheatricaldynamicrange

Highervaluesandalternativecurvestendtogenerateroundingerrorsinthedarkareas,creatingartifactsinJPEGencoding.

EclairColor use ACES AP1 primaries, which contains Rec2020 triangle but also other potentialmonochromatic primaries based color spaces while having a better usage of code values than X’Y’Z’,resultinginsmallerroundingerrors.Thisresultsinbetterefficiencyofthecompression.WeusethesamevirtualwhitepointlogicasDCItoallowfordifferentcreativewhitepoints.

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DCIP3encodedinACESAP1container(left)vsX’Y’Z’(right)

SignaldecodingFortheelectroopticaltransferfunction,wetookthelogicofITUBT1886thatprovidesawaytocompensateforblackperformance,consideringthevariationinenvironment.Weuseagammaof2.8intheequationandareferencepeakwhiteof103nits.

TherenderingofthecontentwouldbeusingtheEOTFasfollow:

Lproj= Lpw1/gamma-Lb1/gamma gamma

max V+b ,0 gamma

where:

bisgivenbyb= Lb1/gamma

Lpw1/gamma-Lb1/gamma,

gammaisthepowercoefficient:2.8

Lpwisthepeakwhiteoftheprojector:103nits

Lbistheblackleveloftheroom

Lpwistheluminanceofpeakwhite

Lprojistheluminanceindicatedbytheoutputsignal

Visthenormalizedbytheinputsignal

Thisdecodingallowsforcompensatingtheblackleveloftheroom.Thismakestherenderingoftheimagemuch closer to the original artistic intent and adaptable to the theater performance. It doesn’t fullycompensateforprojectortechnologydiscrepancies,butthenon-linearityofthisparameteriscomparabletothenon-linearityoftheroomreflectivity,includingattendance.

EclairColor Rev17

ConclusionEclairColorisnotonlyaboutHDR,itismeanttoprovidethemoviegoeranexperienceascloseaspossibletowhatthecreativeteamvalidatedinthemasteringroom.TokeeptheEclairColorquality,theatersarecertifiedbythevalidationofasetofspecificationsregardingroomreflectivity.Constantmonitoringandregularprojectormaintenancearealsokeyinmaintainingthequalityofthebigscreenexperience.

ContactsFortechnicalquestionsaboutEclairColor:cedric.lejeune@eclair.digital

Forothertopics:contact@eclaircolor.com

ÉclairandEclairColoraretrademarksregisteredbyYmagisGroup

EclairColorisprotectedbyseveralpatentsregisteredbytheYmagisGroup.

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Bibliography

DigitalCinemaSystemSpecificationshttp://dcimovies.com/specification/DCI_DCSS_v12_with_errata_2012-1010.pdf

SMPTECinemaStandardshttps://www.smpte.org/lifewithoutsmpte/SMPTECinemaStandards

ITUR-BT1886https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1886-0-201103-I!!PDF-E.pdf

BBCHybridLogGammahttp://www.bbc.co.uk/rd/sites/50335ff370b5c262af000004/assets/57d11dee06d63ee7c8046a86/BBC_HDRTV_List_OfStandardsAndPublications.pdf

DolbyVisionwhitepaperhttps://www.dolby.com/us/en/technologies/dolby-vision/dolby-vision-white-paper.pdf

DolbyICtCpWhitePaperhttps://www.dolby.com/us/en/technologies/dolby-vision/ICtCp-white-paper.pdf

DCIrequirementimages–dynamics,MattCowen,EntertainmentTechnologyConsultantshttp://www.etconsult.com/

HDRTechnologies,TomShulte,JoelBarsottihttp://files.spectracal.com/Documents/White%20Papers/HDR_Demystified.pdf

ACESworkflowhttp://www.oscars.org/science-technology/sci-tech-projects/aces

Qualityassessmentframeworkforcolorconversionandperception,F.Helt,HTS,SMPTE2014http://ieeexplore.ieee.org/document/7269353/

Contrastratiointhetheatricalenvironment,TomBert,Barcohttp://www.barco.com/en/News/Post/2015/10/29/The-contrast-question-1-hyperinflation-in-contrast-land

HDRPerceptionchallengesandmeasureinthetheatricalenvironment,F.Helt,HTShttp://ieeexplore.ieee.org/document/7819602/

DeployingWideColourGamutandHighDynamicRangeinHDandUHD,SMPTEMotionImagingJournal,April2015,CharlesPoynton,JeroenStessen,RutgerNijland http://ieeexplore.ieee.org/xpl/tocresult.jsp?isnumber=7306340&filter%3DAND(p_IS_Number%3A7306340)&pageNumber=2

WikipediaHDRArticlehttps://en.wikipedia.org/wiki/High-dynamic-range_video#SL-HDR1

EclairColorprojecthttp://www.eclaircolor.com

EclairColorPatents FR1770021&EP17305208.5http://www.epo.org

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