calibrationoperation-panasonicplasmamonitors-2009-07

8/2/2019 calibrationoperation-panasonicplasmamonitors-2009-07

1/12

CALIBRATIONANDOPERATIONOF

PANASONICPLASMAMONITORS

JULY2009

Overview

Plasmavideomonitorsprovidehighresolutionimageswithexcellentcontrastanddynamic

range,lowblacklevels,andsaturatedcolorsoververywideviewingangles.Theperformanceof

acalibratedplasmamonitorisveryclosetothatofacalibratedreferenceCRTmonitor.

However,plasmamonitorsperformbestaftercalibration,asopposedtosimplybeingusedwith

theirfactorysettings.Theusermenuprovidesseveraltoolstoeffectcalibration,eachofwhich

willbediscussedinthispaperaspartofastepbystepcalibrationprocess.

Plasmaimagingtechnology

Toobtain

the

best

results

from

aplasma

monitor,

its

useful

to

understand

the

underlying

processthatproduceselectronicimages.Plasmadisplaypanels(PDPs)containthousandsoftiny

pixels,eachofwhichcontainsared,green,orbluecolorphosphorcoating.

Electrodesonthefrontandbackofeachpixelareusedtodischargeelectricitythroughthepixel.

Amixtureofneonandxenongaswithinthepixelisstimulatedbythisdischarge,andemitsa

broadspectrumofelectromagneticenergy,includingaburstofultraviolet(UV)light.

Initially,ahighvoltagechargeprimesthepixelstobeaddressed,followedbylowervoltage

pulsesthataddresspixels,linebyline.Athird,higherdischargevoltagethensustainsallpixels

turnedonduringtheseconddischargecycle.

Figure1.Crosssectionofaplasmapixel.

Becausetheresponseofthepixelisbinary,i.e.onoroff,grayscaleimagesofvaryingintensity

canonlybecreatedbyusingrapidonoffcycling,withthegrayscalevaluederivedfromtheratio

ofontooffcycleswithinaspecifictimeinterval. Thehumaneyeintegratestheserapidpulses

intolighterordarkershadesofgrayandcolor.

1


2/12

Thistechniqueisknownaspulsewidthmodulation,andwhileitcanbeconsideredadigital

imagingprocess,theresponseofthecolorphosphorstoUVstimulationisverymuchanalogin

nature.

Asyoumightexpect,thecontinuouscharge/dischargecyclecreatesheatwithinthepixels.

Plasmatechnologyhascomealongwayinpowerefficiencysincethefirstcolorplasmamonitors

wereintroducedin1993,andtodaysplasmamonitorsaremuchmoreefficientandruncooler

thanevenmodelsfromtenyearsago.

Still,plasmatechnology(likeCRTs)employscurrentlimitingcircuitrytominimizeheatand

prematureagingofthecolorphosphors.Asaresult,peakbrightnessreadingsonplasma

monitorswillvaryconsiderablybetweenthosetakenwithasmallwhiteareatestpatternanda

fullwhitescreen.Fullscreenreadingswillalwaysbemuchlowerthansmallareareadings

becauseofthisfeature,whichisincorporatedintoeveryplasmamonitorbyallplasma

manufacturerstolimitpowerconsumption.

MonitorCalibration Readings

Tocalibrateaplasmamonitor,youwillneed(attheleast)acolorimeter,eithercontactornon

contacttypes.(Handheldmeterscanalsobeusedwithcontactsensors.)Moreadvancedcolor

sensingdevicessuchasspectraradiometersandphotometerscanbeused,althoughtheseare

commonlyusedforextremelyprecisemeasurementsofnarrowbandsinglecolorintensityand

huevaluesfromelectronicdisplays.

Therearenumerousbistimulusandtristimuluscolorimetersavailableforreasonableprices.

ThesesystemsusuallyconsistofasensorheadthatconnectstoanotebookordesktopPCvia

USBconnections,plusapplicationssoftwaretologandinterpretthereadings.

Figure2.AnotebookPCbasedcolorimeterwithcontactsensor.(PhotocourtesyDatacolor)

Thereadingsandcompileddatapointsshouldincludemonochromatic(white)luminancevalues

(eitherincandelaspersquaremeter(metric)orfootLamberts(English),colorluminanceand

huevalues,alsoexpressedasx,ycoordinatesonthe1931and1976CIEcharts,andcolor

temperaturevalues,expressedinKelvins.

2


3/12

Itisalsoextremelyhelpfultohavethecolorimeterssoftwareplothistogramsforluminance

responsevs.drivingvoltage(gamma),colortemperaturetrackingatdifferentluminancevalues,

andtrackingofred,green,andbluelevelsatdifferentluminancevalues.Theseplotsare

essentialtodeterminetheplasmamonitorsgammaresponsebeforeandaftercalibration.

Thecalibrationsoftwareshouldalsogenerateacolorgamutchartforthedisplay.Thischartwill

showtheoperatingcolorgamutoftheplasmamonitor,comparedtoastandardgamutsuchas

theITUBT.709standardcolorspacefordigitalTV.Suchachartisessentialforfinetuninghue

andluminancevaluesforprimarycolorstoconformtodifferentstandardcolorspaces(where

suchfinetuningcontrolsareavailable).

MonitorCalibrationTestPatterns

Yourcalibrationwillalsorequireaprecisiontestpatterngeneratorwiththeappropriateanalog

ordigitalsignalinterface,suchascomponentYPbPr,RGB,HDMI,DVI,orSDI/HDSDI.This

generatorshouldcontaintestpatternsfor:

(1)Grayscale

adjustments

(full

black

and

white,

50/50

black

white

fields,

small

area

windowsinstepsofatleast10IRE,andcheckerboardblack/whitetestpatterns)

(2) Coloradjustments(fullandsmallarea100%red,100%green,and100%blue,pluscyan,

yellow,andmagenta)

(3) Pixelclockandimagepositionadjustments(crosshatchandover/underscanpatterns,

finetextpatterns)

Youmayalsofindadditionaltestpatternstobeuseful,includingluminanceandchrominance

multiburstpatternstoshowfrequencyresponseoftheplasmamonitorandanyassociated

imageprocessing/switchingelectronics.

Figure3.Allowa1hourwarmupcycleforanynewplasmamonitorbeforecalibration.

3


4/12

CalibrationSteps

A250hourpreagingcycleisstronglyrecommendedforallnewPanasonicplasmamonitors.

ThispreagingcycleisbuiltintoSeries11andlatermodels,andisaccessiblefromthemenu.

Afterthepanelhasbeenaged,thefirststepistoturnonyourplasmamonitorandletitwarm

up.Thisbriefidlingperiodwillstabilizethemonitorandresultinamoreaccuratecalibration.A

fullscreen,50%whitetestpatternshouldbeusedduringthisidlingperiod.Donotusea100%

whitetestpattern.

Beforecalibration,youshouldselectStandardorCinemamodesfromthelistoffactoryimage

presets.TheDynamicpresetwillpresentthebrightestimages,butthegammaresponseofthe

displayisverynonlinearinthismode,typicallyresemblinganScurve.Thismeansthedisplay

comesslowlyoutofblack,thenrisestooquicklytowardswhitebeforeclippingthehighestlevels

ofwhite.Chooseagammasettingof2.2forinitialcalibration.

DisableanyimageenhancementssuchasdynamicgammaandAGCmodes.Thesewillhavea

negativeimpact

on

gamma

performance.

TheonlysignificantdifferencebetweenStandardandCinemamodeswillbethestartingpoint

forcolortemperatureadjustments.InStandardmode,thecolorofgrayissetbythefactoryto

7500K,whileinCinemamode,itismuchlower,rangingfrom5800Kto6000K.Thereisenough

rangeintheRed/Green/Bluehighandlowadjustmentstoraiseorlowerthemeasuredcolor

temperaturetothenormal6500Ktargetforvideoimaging.

OnesuggestionistocalibratebothpresetsanduseStandardasavideo(2.2gamma)viewing

mode,whileCinema(2.5)gammacanbeusedtopreviewcontentmasteredfordigitalcinema

projection.Athirdfactorypresetmode(Monitor)presentsimagesthataremuchdimmer,but

are

supposed

to

emulate

SMPTE

theater

brightness

levels

approximately

14

ft

L,

or

50

cd/m

2

.

Figure4.Asmallarea100%whitewindow,usedforpeakbrightnesscalibration.

4


5/12

AdjustingDynamicRangeWhiteLevel

Whileplasmamonitorsarecapableofveryhighluminancereadingsfromsmallarea100%white

windows(over180cd/m2

or52ftL),theirgammaperformanceisnotstableatsuchhigh

brightnesslevels.

Agoodtargetisapeaksmallareabrightnessreadingof100cd/m2,whichisequivalentto29.23

ftL.Thecolorimeterissettotakeasimpleluminancereading,andasmallarea100%whitetest

patternisusedtosetpeakbrightness.NotethatthemonitorsPicture(Contrast)adjustmentis

usedhere,nottheBrightness(blacklevel)adjustment.

Although100cd/m2isausefullevel,plasmamonitorsarecapableofhigherpeakbrightness

levelswhilemaintainingstablegammaperformance.Inpractice,amaximumbrightnessvalueof

120to130cd/m2canbeused(35to38ftL)beforegammaperformancebeginstosuffer.

However,thispeakbrightnesslevelismuchhigherthanthatrecommendedforprofessional

videomonitorsbystandardsorganizationssuchasSMPTE.

Figure5.PLUGEpattern,showinglogarithmicgrayscale(right)and5%whitebar(left).

AdjustingDynamicRangeBlackLevel

Thenextstepistosetthedisplaysblacklevel.ThisisdonewiththeBrightness(blacklevel)

adjustmentandasuitabletestpatternthatconformstotheblacksetuplevelofthecontent

beingdisplayed.Blackcanbeseteitherat0IRE(0ona0255RGBscale),or7.5IRE(16ona0

255RGBscale).

APLUGEtestpatternisgenerallyusedtosetblacklevel.Thispatternconsistsofafourstep

logarithmicgrayscaleontheright,andtwoblackbarsthatrepresentlevelsaboveblackthat

measure2.5and5%,respectively,whengeneratedfromanRGBvideocard.

Whenoriginatingfromatruevideopatterngenerator,the2.5%barisactuallybelowblack,as

thevalueofvideoblackis7.5IRE.Sotheblacksettingonyourplasmamonitorisdependenton

yourvideo/RGBsourceandthevalueofblacksetup.

5


6/12

Notethatthewhite(contrast)settingisnottouchedduringthispartofthecalibration.What

youaredoingissettingtheupperandlowerlimitsofthemonitorsdynamicrange,i.e.the

lowestlevelofblackandthehighestlevelofwhite.Makesurethatanyimageenhancements

areturnedOFFintheimageadjustmentmenu,suchasdynamiccontrastandpictureAGC.These

willcausethelevelsofblackandwhitetovarydynamicallywithcontent.

MeasuringDynamicRangeAndGamma

Atthispoint,itsagoodideatomeasurethedynamicrangeandgammaoftheplasmamonitor.

Thiscanbedonein10IREstepswithsoftwarethatplotstheresultinggammacurves

automatically.Theresultingplotwillshowthelowestluminancelevel(black),thehighestlevel

(white),andhowthedisplaycomesoutofblack.SoftwaresuchasColorFactswillhavewizard

applicationstoruntheemeasurementsautomatically.

ThegoalisemulatetheperformanceofCRTsandcomeascloselyaspossibletostandard

gammacurves,suchas2.2forvideoand2.6fordigitalcinema.Althoughindividualgamma

correctionforred,green,andbluechannelsisnotincludedinthestandardpicturemenu,

adjustingthe

black

level

setting

in

combination

with

one

of

the

gamma

presets

will

result

in

a

slightlysteeperorshallowerclimboutofblack.

Figure6.LuminancehistogramforaTH42PF11UK,aftercalibration.Gammacalculatesto2.22.

Theresultinggammacurvesshouldarccorrectlytowardswhitewithnoevidenceofclippingor

whitecrush.Ifeitherisseen,thecontractcontrolmustbeturnedbacktoreducepeak

brightness.Then,runagrayscalestepmeasurementseriesagaintoverifyconsistentgamma

performance.

Onceasatisfactorygammacurve(orcurves)hasbeenachieved,thenextstepistoadjustthe

colorofwhite.

6


7/12

CalibrationOfColorTemperature

OnCRTmonitors,thereareusuallytwosetsofcontrolsforadjustingcolortemperature.Oneset

controlsindividualgain(contrast)forthered,green,andbluechannels,whiletheotherset

controlsbias(cut)forred,green,andblue.Gain(orHigh)isusedtomakeadjustmentsinthe

upperendofthegrayscale(40100IRE),whilebias(orLow)isusedbelow40IRE.

Becauseplasmausesapulsewidthswitchingmodetocreateimages,therereallyarentany

gainandbiascontrolsperse.Instead,thereareHighandLowsettingsforeachprimarycolor.

Pictureinformationisreproducedonaplasmadisplaybytheuseofsubfieldaddressing,even

thoughthevoltagesintheprimingcharge,addressing,sustain,andclearingcyclesremain

constant.

Asaresult,theLowadjustmenthasmuchlessofaneffectthantheHighadjustmentforeach

primarycolor.Evenso,itsstillpossibletogetconsistenttrackingofaspecificcolortemperature

justaboveblacktofullwhite,withavariationof250Kelvinfrom20IREto100IREnotunusual.

ThisperformanceisconsistentwithevaluationgradeCRTmonitors.

Figure7.Smallareawindowsat20IRE(left)and80IRE(right).

SettingHighColorTemperatureValues

Tostart,selectanearwhitesmallareawindow,suchasa70or80IREpattern.Attachthe

sensortothescreensoitiscenteredinthewindow.Next,launchthecolorimetersoftwarethat

readsoutx,ycoordinatesforthecolorofwhite,using6500Kasthetargetvalue.Setthecolor

temperatureontheplasmamonitortoNormalasastartingpointthiswillrunalittleonthe

coldside,above7000Kelvin.

Watchingasthecolortemperaturereadingupdatescontinuously,adjusttheHighcontrolsfor

red,green,

and

blue

individually

to

come

as

close

as

possible

to

the

desired

locus

of

.313x

and

.329y.Therewillbesomeinteractionbetweenthesedriveadjustments.

ItsalsoveryhelpfultorunanRGBlevelhistogramsimultaneouslywhilemakingthese

adjustments.Thehistogramwillshowthelevelsofred,green,andbluechangeasyoumake

adjustmentstothewhitepoint.Thismakestheprocessmoreintuitive.

7


8/12

Figure8.ColortemperaturehistogramforaTH42PF11UK,showingRGBlevelsacrossthegrayscale.

SettingLowColorTemperatureValues

OnceyouhavecalibratedtheHighsettings,switchtoa20or30IREsmallareawindowand

repeattheprocess,thistimeusingtheLowadjustcontrolsforred,green,andblue.Notethat

youwilllikelyseemuchwiderswingsincolortemperaturewithincrementaladjustmentsto

eachcolorchannel.Thisisnormal.YoumaynotbeabletogetasclosetoD6500inLowmodes

asyoucanwithHighsettings.

Onceagain,anRGBlevelshistogramwillmovethisprocessalongmuchmorequickly.Itwillalso

preventyoufrommakingerroneous,grosscorrectionstooneormorecolorchannelsasyou

worktowardsaneutralgrayvalue.Also,thetwosetsofcontrolswillinteractwitheachother,

andyouwillprobablyseethatyourHighsettingswillneedtobeadjustedagainafteryouhave

calibratedtheRGBLowsettings.

MeasuringColorTemperature(Grayscale)Tracking

Afteryouhavecompletedyouradjustments,runagrayscaletrackingwizardtoseejusthow

closelyyourplasmamonitortracksto6500K.Youcanalsodothisstepbystep,startingatblack

(typically7.5IREonmostgenerators)andmovingto10IRE,thenupto100IREin10IREsteps.

Someprogramswillplotgamma,colortemperaturetracks,andRGBhistogramsforyou,allat

thesametime.

Ifyouaresatisfiedwiththeresults,youcanmovetoanotherimagepresetmodethatyoud

calibratedforadifferentgammacurve,andrepeattheHighLowRGBadjustmentprocess.Dont

besurprised

to

see

large

shifts

in

color

temperature

at

both

ends

of

the

grayscale,

as

you

select

differentgammasettings.

Saveyoursettingsaftercompletion.Theywillberetainedinmemoryevenafterthedisplayis

powereddown. Itsalsoagoodideatowritedownyoursettingsandkeepthemwiththe

ownersmanual.Ifyourcolorimeterchartscanbeprintedout,makeacolorcopyandkeep

thoseonhandforreferencewhendoingfuturecalibrations.

8


9/12

Figure9.Acolortemperaturehistogram(white)foraTH42PF11UK,overlaidonthedesired6500Ktargetline.

CalibrationForVideoInputs

Thiscalibration

involves

setting

color

saturation

and

hue

for

SD

and

HD

input

signals.

Nite

that

hueadjustmentsmaynotbepossiblewithdigitalinputs,suchasSDI,HDSDI,andDVI/HDMI.

Youwillneedacolorbartestpatterntomakethisadjustment.Connectthetestpattern

generatortotheinputyouwanttouse,inthesameanalogordigitalsignalformat.Also,match

theresolutionoftestpatterngeneratortothatoftheinputsignalsyouwillbeconnectingtothis

input.

Bringupthecolorbartestpattern.Lookingthroughabluefilter,adjusttheplasmamonitors

colorsaturationcontroluntilthelongandshortwhiteandbluebarsegmentsexhibituniform

intensityfromtoptobottom.Next,adjustthehuecontroluntiltheshortandlongmagentaand

cyanbarsegmentsareequalinintensity.

Atthispoint,thesaturationandhuelevelsaresetcorrectly.Notethatthesearedifferent

adjustmentsthanthosemadeforcolortemperatureandwhitebalance.

Figure10.Fullcolorbarpattern(left)andcolorsaturationandhueadjustmentbarshighlighted(right).

9


10/12

Figure11.Outlinedareasshowbarstoadjustforcolorsaturation(left)andhue(right).Whensetcorrectly,the

saturationandhuebarswillhavethesameintensityfromtoptobottom.

AdditionalMeasurementsAndCalibrations

Contrast:Usingacheckerboardpattern,youcantakeanANSI(average)contrastreadingand

calculatearealistic

intra

scene

contrast

ratio.

Log

the

eight

white

square

readings;

add

them,

andthentaketheaverage.Repeatthisprocessfortheeightblacksquares.Notethattheblack

readingswilltakelonger,duetothelowersensitivityofthemeasuringinstrument.

Now,dividetheaverageblackreadingintotheaveragewhitereadingtodeterminetheANSI

contrastratio.Youcanalsocalculateapeakintrascenecontrastratiobydividingthelowest

blackreadingintothehighestwhitereading.

Ifa50/50white/blacktestpatternisavailable,youcancalculatepeakcontrastthatway.Takea

measurementnearthecenteronthewhiteside,andthenrepeatontheblackside.Dividethe

blackintothewhitefortheresults.Sequentialcontrastreadingsinvolvemeasuringaquiescent

screen(poweredon,butnosignalpresent)andthena100%white,smallareawindow.Divide

theblackreadingintothewhitereadingtogetasequentialcontrastcalculation.

Figure10.A16blockcheckerboardcontrasttestpattern,showingmeasuringpoints.

10


11/12

Tip:Whenmeasuringlevelsofblackandalsowhenrunningagrayscalewizardseriesto

determinegammaperformance,RGBhistogram,andgrayscaletracking,makesurethatambient

lightiskeptawayfromthesensorasmuchaspossible.Onewaytodothisistodrapethefront

ofscreenwithlightabsorbent,largelyopaquematerial,suchasthickvelvetstipplefabric.Cover

theentirescreenandthecolorimetersensor,thentakeyourreadings.

FrequencyResponse:Youcanusealuminancemultiburstpatterntocheckfrequencyresponse

upto1920x1080pixels.Thiswillusuallyinvolveapatternwithafrequencyabove30MHz.It

mayalsobeoneofanytestpatternsthatstartatlowerfrequenciesandmoveupwards.Thefine

delineationsbetweentheblackandwhitetransitionsshouldbevisibleatthisfrequency,

particularlywhenusingadigitalvideosignalinterface(SDI,DVI,HDMI).

Tip:Makesuretheplasmamonitorisinpixelbypixel(1:1)modebeforecheckingfrequency

responsewitha1920x1080testsignal.Otherwise,themultibursttestpatternwillnotappear

correctly.

Figure11.Luminancemultiburstpatterns,showingfullfrequencyresponse(top)andhighfrequencyrolloff(bottom).

BrightnessAndColorTemperatureUniformity:Youcanmeasuretheconsistencyofboth

brightnessandcolortemperatureacrossyourscreenwithacolorimeter.Takemeasurements

withafullwhitetestpattern,allowingaboutfiveminutesforanyAGCcircuitrytosettle. Divide

thescreenintonineimaginarysectionsandtakeacombinedluminanceandcolortemperature

readingineach.

Addthereadingsanddeterminetheaverageofall.Dividethatbythebrightestreading,whichis

usuallythecenterreading.Theresultwillbeafraction(lessthan1),typicallyinthehigh90%

range.

Nowsubtractthelowestcolortemperaturereadingfromthehighesttomeasurethetotalshift

acrossafullwhitescreen.Thisshiftshouldmeasurelessthan250Kelvin.Eachtimeyou

recalibratethe

monitor,

run

another

series

of

nine

combined

brightness

and

color

temperature

uniformityreadingstocheckforexcessivedifferentialagingofthephosphors.Whenoperatedat

normalbrightnesslevels,thephosphorsshouldageataconsistentrateacrossthescreen.

Tip:Itisnormalformanyimageadjustmentstointeractwitheachother.Thiseffectismost

pronouncedwhenadjustingred,green,andblueHighandLowsettings,butyoumayalsosee

interactionbetweencontrastandbrightnessadjustments,particularlywhensettingblacklevels

andmeasuringgammacurves.

11


12/12

12

calibrationoperation-panasonicplasmamonitors-2009-07

Documents