Dinh Nghia Va Cach Su Dung-1

8/9/2019 Dinh Nghia Va Cach Su Dung-1

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VRay nh ngha v cch s dng: Phn1

M u

Trong cc chng trnh render cho 3dsMax, Vray l mt chng trnh c s dngph bin nht. Hon ton khng phng i khi ni Vray ph bin n mc bng tng ccrenderer khc nh mental ray, finalRender brasil r/s cng li. iu cng th hin rvi thut ton v nhn ca chng trnh c nghin cu v hon thin bi mt nhmngi.

Tnh ph bin ca chng trnh c nhng nguyn nhn xc ng. Th nht, VRaydng trong cc php tnh ca n phng php chuyn i tnh ton n c xy dng

hon ton trn c s ca phng php Monter-Carlo. Trong phng din ny c th VRayc dng nh l 1 v d trnh din chng trnh theo phng php Monter-Carlo.Nhng ngoi ra, VRay c 1 lot i mi th v cc cng ngh x l, cung cp thm choVRay nhng u th trong cht lng v tc tnh ton. Bi vit ny s trnh by v cc cch tnh ton c bn bn trong VRay v cung cp cho ngi c mt s phng php sdng hiu qu chng trnh ny.

Cc nguyn ly c bn


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Nhim v c bn ca bt k chng trnh renderer no l tnh ton s chiu sng vmu sc ca mt im bt k ca khung cnh 3 chiu. Nhim v rt l phc tp. Ccphng php tnh ton ca ha my tnh vt qua mt chng ng pht trin khdi, trc khi ngi ta t ti trnh nh ngy nay v hin thc ha cc bc nh bng strnh din ca my tnh.

Th nht, chng ta bit rng cc vt th c ngun sng chiu sng trc tip, khim vt th v ngun sng c th ni vi nhau bi mt ng thng. M hnh s chiu sngFong v m hnh bng Fong, nhng th cho php lm mm mu ca cc poligon bmt v tnh ra nhng ch sng ni bt highlight, tr thnh nh cao ca m hnh tnhton ny. M hnh chiu sng cng nh cc php bin i ca n (Lambert, Blin,Torrent, Ward v nhng ci khc) by gi vn l nn tng tnh ton s chiu sng trctip, ch thm 1 cht b sung. Mt trong cc b sung quan trng nht , s tnh ton cc kchthc khng gian ca ngun sng, cho php nhn c cc vt m ca bng vt th. Mtb sung khc l xc nh s gim dn cng nh sng theo khong cch. V chi tit, ccphp tnh vt l chnh xc s chiu sng s dng nh lut cng tia sng gim dn theo

bnh phng khong cch.Thnh phn th hai ca s chiu sng vt th c xc nh bng phn x (hay gn

vi n) t cc vt khc v khng gian xung quanh vt th. thc hin php tnh ngita ngh ra phng php d tia - ray tracing. Phng php ny d theo ng i ca cctia sng, bt u t Camera, ti b mt u tin v sau ph thuc vo tnh trong sut hayphn x ca b mt, xc nh hng i tip theo ca tia sng. Phng php d tia t cameraln u tin cho php tnh n mi trng xung quanh trong s chiu sng vt th v hiu qu hn s d tia t ngun sng, bi v ch tnh xem xt n cc tia sng ti ccamera. Mt trong nhng nhc im ca phng php d tia c in l tnh cng nhcca hnh nh nhn c, s r rng qu mc ca cc ng bao, bng v mu sc. V

th sau ngui ta lm ra php chnh sa s phn b d tia - distribution ray tracing(DRT). Bn cht ca DRT l ch trong mi ln giao ct gia cc tia d t b mt trnng i ca n, t mi im giao nhau c xy dng khng ch mt m nhiu tia sng.Qu trnh ny phn no gi nh n chui phn ng. Hng gii quyt cho php tnhra cc phn x v khc x yu dn (nh l cc phn x v khc x fuzzy, blurry hayglossy), nhng m km theo s gia tng ng k khi lng tnh ton. M hnh DRT cthc hin trong cc tnh cht ca vt liu VRay phn x v khc x vi s gip cathng s Glossy. Do ci gi qu t ca cc php tnh DRT, s chm chp trong tnh tonglossy-material VRay tr thnh iu m ai cng ni n.

Thnh phn th ba ca qu trnh chiu sng vt th c tnh ton qua s khuch tnnhiu ln mu sc ca cc i tng xung quanh. Phng php u tin dng tnh schiu sng khuych tn th cp l radiosity, mc d vn c s dng cho ti gi, vi stn ti mt lot yu km, n nhng ch cho 2 phng php tnh khc tin b hn Phng php Monte-Carlo v phng php Photon map. Phng php bn photon tora cho mi mt phng ca i tng trong khung cnh m t c s d liu, trong lu trthng tin v s va chm ca photon vi b mt - ta va chm, hng v nng lng caphoton. Photon c hiu l phn nng lng ca s chiu sng, truyn theo mt hngnht nh t ngun sng. Mt photon ca bn c dng trong cc tnh ton tip theo


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nh gi s chiu sng ca im trong kt qu ca s phn tn khuych tn nh sngtrn cc b mt xung quanh. Tt c cc renderer, s dng phng php bn photon, thchin s tnh ton chiu sng qua 2 bc. Bc th nht thc hin d photon t ngun sngn b mt v to ra bn photon cho chng. Bc th hai thc hin qu trnh d tiangc li t camera, cn bn photon c s dng tnh ton s chiu sng khuch

tn ca cc im giao nhau gia tia d ngc vi mt phng.Th t, s chiu sng c xc nh bng cc trng hp c bit tnh cc hiu

ng nh sng xut hin trong kt qu t vo tiu im do s khuch tn v phn x ca tiasng trn mt s vng ca b mt. Cc hiu ng ny c gi l cc hiu ng quang t(caustic) ca s chiu sng, m minh ha tuyt vi t thc t c th l thu knh hi t nhsng mt tri ln b mt vt th.. S tnh ton cc hiu ng quang t ca nh sng cthc hin bng phng php bn photon, nhng vi yu cu bn photon cc b cmt rt cao. V th cc bn photon c to ring bit vi s xut hin cc nhu cu.

kt thc cc ni trn, c th khng nh rng: vi trnh pht trin hin nay ca

cc phng php tnh ton ha my tnh cho php tnh ton s chiu sng mt im btk trong khung cnh 3D nh tng ca 4 thnh phn: chiu sng trc tip, phn x v khcx, pht tn khuch tn th v cc hiu ng quang t nh sng.

tnh ton chnh xc tt c nh sng, i qua 1 im no y trn mt phng, cnphi tnh tng tia sng, i ti im t mi hng. iu dn n s cn thit tch phnnh sng theo na bn cu, bao quanh im, nu im nm trn 1 b mt khng trong suthoc theo hnh cu bao xung quanh nu im nm trn mt b mt trong sut. tnh tonb nh sng trong ha my tnh s dng cc hm, miu t 4 thnh phn nh sng hmngun sng, hm ca cc tnh cht phn x (l tng), khc x ca cc b mt v hmkhuch tn cc phn x ca cc b mt. Hai hm cui thng c hp nht v c gi l

BRDF - Bidirectional Reflectance/Refractance Distribution Function (hm r nhnh phnb phn x/khc x). Mt khc php tnh gii tch chnh xc ca cc tch phn nh vytrong hu ht trng hp l khng th, v th tm ra kt qu cc php tnh khc nhau c s dng

Mt trong cc phng php c bn l phng php Monte-Carlo. Trong tng cbn, phng php Monter Carlo cho php tnh ra gi tr tch phn nh tng ca mt slng khng ln gi tr ca cc hm di tch phn, c chn ngu nhin. Thc t,phng tin ton hc ca phng php Monter Carlo cho php xc nh s la chn nhnggi tr , bi v ph thuc vo n l s chnh xc v tc tm ra kt qu tch phn. cla chn tnh gi tr ca cc hm di tch phn thng c gi l samples. Hin ti,phng php Monter Carlo l tiu chun bt thnh vn cho cc render ha my tnh 3chiu v c s dng ht sc rng ri hu nh trong phn ln cc chng trnh hngu. Mt khc phng php c mt nhc im nghim trng chm chp trong tmkt qu. C th iu c ngha l, tng cht lng tnh ton nh sng, v d ln 2 lnth khi lng tnh ton s tng gp 4 ln (s sample). Yu km trong render l nhng vtbn mu, cc ht v s gi to trn


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Phng php Photon map c thit k nh s xen k ca php tnh s chiu sngkhuch tn th cp bng phng php Monter Carlo v thay th php tnh tch phn tngng. Gii php c mt lot u im v c nhc im. u im chnh ca Photon mapl tc v s hon chnh ca php tnh. Cc nhc im ca n lin quan n nhng yucu b nh ln v s kh khn trong vic lin kt cc vt ni, cc gc v ng bin ca b

mt.Chng trnh ct li ca Vray c xy dng trn phng php Monter Carlo . Vray

cng s dng phng php Photon map, nhng khng nh s xen k vi phng phpMonter Carlo (ging nh trong Mental ray), m nh mt s b sung. Ni c th hn l, tnh khuch tn s cp (tia sng t ngun i n b mt, phn chiu v va vo im cn tnhsng) trong Vray s dng phng php Monter Carlo. Dnh cho tt c cc khuch tn tiphn x, bt u t ln th 2 ( tia sng ln th 2 hay nhiu hn phn chiu t cc b mtkhc trc khi n im cn tnh), c th s dng phng php Monter Carlo cng nhphng php Photon map. Trong thut ng ca Vray, khuch tn ln th nht c gi lFirst diffuse bounces s bt ln th nht, tt c nhng s ti phn x khc - secondary

bounces, hay l s bt ln th cp. Cch tip cn kh hp l bi v nh ta r, phnchnh nh sng khuch tn ca im c to thnh t chnh s phn x th cp. ng gpca cc qu trnh phn x cn li khng ln, do kt qu ca s gim rt nhanh ca cng phn x khuch tn cng vi qu trnh gia tng s lng ca chng. Bng cch , skt hp phng php Monter Carlo v Photon map trong Vray m bo tnh chnh xcv tc cao hn trong tnh ton, so vi cc chng trnh render i th khc

S dng Photon map cho tnh ton phn x qua li c a thch hn nhiu ln bi vn cho php nhn c kt qu nhanh hn v cht lng hn. Mt khc, v Photon mapkhng th lm vic vi cc ngun sng nh Skylight, HDRI v hn ch truy cp vo bnh, trong tnh ton khung cnh m v trong mt vi trng hp khc Photon map thng

c thay th bng phng php Monter

Cc thng s iu khin ca VRay

VRay: QMC Sampler

Nhm cc bin iu khin trong Vray bng cc tnh cht chung ca phng phpMonte-Calro, t trong bng di y:


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Gi tr cc thng s ny xc nh cc Sampler s c s dng trong tnh ton migi tr theo phng php Monter-Carlo. Ghi nh l thc t tt c cc gi tr, c tnh biVray, tt c cc dng chiu sng, khc x v phn x, translucency, caustic v cc loikhc, u s dng phng php . Kt qu l ph thuc vo nhng xc lp ny tc tnhton cng nh chnh xc v do ko theo mi quan h thi gian/cht lng render

hnhLock to pixels c dng loi i nhng im nhp nhy trong hot cnh. Nu du

tick c nh trong trng bn cnh thng s ny mt lin kt cht ch ca gi tr ccim cn tnh s c s dng i vi cc im ca hnh sao cho cc gi tr ging nhautng ng vi cc im trong cc hnh (frame) lin k. Phng php Monter Carlo c tnhngu nhin v th vi s gip ca n cng mt gi tr c th nhn nhng kt qu hikhc nhau trong cc iu kin tng t. Nu ta tnh nh tnh th gi tr ny c th mnh dn ch tt. Lock to pixels v tng samples cho tnh ton cc gi tr l 2 phng phpc bn chng li s nhp nhy (flickering) trong cc hot cnh c tnh bi VRay

Adaptation by effect on final result (importance sampling) k thut c dng chn cc samples. Trong tnh ton tch phn s chiu sng bng phng php MonterCarlo cc gi tr ca cc hm di tch phn (samples) c chn theo mt qui lut ngunhin no trong gii hn ca hm (bn cu cho tnh sng ca im trn mt khng trongsut v hnh cu cho im trn mt trong sut) s c s dng. Th v l samples c thc tnh hnh hc nh hng, dc theo n cc gi tr ca hm s c tnh - ni mt cchkhc n ging nh t im s sinh ra tia ly samples. K thut importance sampling chn nhng im bng phng php ch trng hay gi tr ca nhng im c th casamples cho mt kt qu c th. Nu tia ly samples dc theo mt hng no em lit gi tr chiu sng hoc thm ch bng 0, cc samples c ly tip theo theo hng hoc gn vi n s khng c ly. Mt v d khc tnh mt khc x ti s khng cn

nhiu samples. Trong mi trng hp, bt thng importance sampling s p buc chuynng ca Vray tm kim v la chn cho tnh ton nhng gi tr ln (v v th quan trnghn cho hnh nh) samples v b i nhng samples c gi tr thp. Gi tr Amount iukhin s cao trong s dng k thut importance sampling khi tnh. Gi tr 0 s tt honton s s dng importance sampling, cn vi Amount = 1 tt c cc samples sphi qua tuyn chn. Trong phn ln trng hp s dng k thut importance sampling htsc hu ch i vi cc renderer a n s gia tng trng thy v tc trong khi vnm bo cht lng tnh ton cao. Mt khc k thut importance sampling vi tnh chtngu nhin ca mnh c th em li nhng kt qu d ngoi mong mun khng phi lmt nghich l, i lc tt thng s c th c li v s lm gim nhiu trong tnh ton.Nh vy gim Amount s dn ti tng cht lng render v tng c thi gian tnh ton.Chin lc vi thng s ny c th l nh sau tng Amount, nu n khng dn n nhngthuyn gim nghim trng v cht lng hnh nh v gim n nu render khng c mt linhiu no c. Theo mc nh Amount = 1

Adaptation by sample values (early termination) cho php Vray phn tch ccgi tr samples v b qu trnh ly samples nu nh nhng g tr gn ging nhau. Nimt cch khc nu nh cc gi tr ca samples t khc nhau th thay v tnh tip cc gi trca samples mi cc gi tr ca samples tnh s c s. Nu nh cc samples khc


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nhau r rt th s lng chng c chn s ln hn. Thng s Amount xc nh mc p dng k thut ny. Vi Amount = 0 k thut ny hon ton khng c s dng, viAmount =1 early termination s dng s lng nh nht c th c cc tia samples. Nunh cn cht lng tnh ton cao th dng Amount = 0, nhng tr gi cho iu l s giatng thi gian rander. Chin lc cho thng s ny ging nh vi thng s importance

sampling , gi tr Amount mc nh = 0.Min. samples Thit lp s lng nh nht c cho php samples. Tc l s

samples dng cho tnh ton 1 gi tr nht nh khng th nh hn gi tr

Noise threshold trng ti, ngi phn s, quyt nh, khi no gi tr nhn c tt cho hnh nh. Cc gi tr kt qu s c t so snh vi nhau theo tng bc. Nu skhc nhau ln hn gi tr Noise threshold th cc samples b sung s c tnh, nu s khcnhau nh hn th qu trnh tnh kt thc. R rng l thng s ny c nh hng trc tipnht ti cht lng ( nhiu ) v tc render. Tng n ln c th lm s tnh ton trnn rt nhanh v nhiu v ngc li

Nhng thng s trnh by trn cho php Vray linh ng nhn cc quyt nh v ssamples tnh ton gi tr ny hoc gi tr kia mt cch trc tip trong qu trnh tnh. NuAmount ca importance sampling v early termination c gi tr l 0 chng ta s nhn crender c kh nng cao nht ca Vray v cht lng. Thi gian tnh cng s l ln nht cns samples s gn vi s subdivs, c nh cho GI trong thit lp ngun. Nu gi trAmount ca importance sampling v early termination bng 1, render s l ti thiu (nhnghon ton khng c ngha l ti) cht lng, thi gian tnh cng s l ngn nht c th ccn s samples s gn vi gi tr nh trong Min. Samples. iu ging nh 2 mt inghch, trong gii hn xc nh mi gi tr thit lp trung gian, tiu tn cho thi gian vcht lng render


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Hnh.02-08. Xc lp c 2 gi tr Amount = 0, Noise threshold=0.005.


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Hnh.02-09. Xc lp c 2 gi tr Amount =1, Noise threshold=0.005.Nhn thy l hnh nh thu c ging ln trc nhng thi gian randergim i 2.5 ln


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Hnh.02-10. Xc lp c 2 gi tr Amount =1, Noise threshold=0.1. Gim Noisethreshold cng tng tc tnh nhng lm ti i r rt cht lng hnh nh (nhiu gcv trn cc vt ni ca tng v sn, xut hin cc ht trong bng )

Cc gi tr t sn trong Vray theo mc nh ca Amount v Noise threshold kh anng v t nhin trong hu ht cc trng hp, hoc chng c th l nhng gi tr khi ucho cc th nghim c nhn. Thay i chng ch nn khi c s hiu bit thc s v su sc.Khuyn co khng nn gi tr 0 cho Noise threshold iu c th dn Vray tinhng vng tnh ton lp v hn, hoc nhanh hn, ti s kt thc thm bi cng vic cachng trnh

QMC Monter Carlo, phng php c s dng bi Vray khc bit vi MonterCarlo c in ch nh vic s dng early termination v importance sampling. Chngcho php chn cc samples , iu lm cho nhng sample ny khng hon ton ngu nhinnh trong phng php Monter Carlo chun


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Tnh GI (Chiu sng ton cnh - Global Illumination)

tnh thnh phn u tin chiu sng trc tip, Vray c ring thut ton c khnng lm vic c lp. chc chn v iu rt n gin, ch cn render 1 khung cnh 3D khng c GI ( b du tick trong hp chn On trong bng VRay: Indirect Illumination).

Trong kho cng c ca modul tnh chiu sng trc tip c kh nng lm vic vi cc ngunsng khng gian nn tnh cc mp bng mm khng to thnh vn g. Cc xc lp chiusng trc tip c trong cc thng s ca ngun sng v bng (s gim dn, loi ngun sng,thng s ca bng v.v..)

Hnh.02-02. Ch tnh chiu sng trc tip. Tt c cc vng khngnm trong gii hn nhn thy ca ngun sng u nm trong bng ti.Bng mm l kt qu ca thao tc vi ngun sng khng gian

Tt chiu sng trc tip hon ton c th lm c, lm iu ta s dng ntExclude trong bng xc lp ca ngun sng. ng dng ny c ch cho phn tch map dng nguyn th v nh hng i vi chng cc xc lp ca cc thng s. V d, tch vt


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th ra khi s chiu sng khng nh hng ti Photon map bi v n, nu trong tnh chtca ngun sng c t Generate diffuse, s tnh ton Photon. Php tnh Photon mp cngch c th tt . Cng c th la chn bt hoc tt cc vt th khi Photon map nu trongtnh cht ca cc vt th xc nh b i du tick trong mc Receive GI Generate GI(trong bng Vray: System>Object settings )

Cng c sn trong Vray thut ton ring tnh d tia ngc, n cng l mt b phnc lp ca h thng tnh. Mt phn thit lp ca ray tracing nm trong bng VRay: GlobalSwitches VRay: Image Sampler (Antialiasing), phn khc trong thng s vt liuVRayMtl.

Tnh ton thnh phn chiu sng th ba khuch tn phn x ca s chiu sng lmt trong nhng thut ton quan trng nht ca Vray v cng tng i c lp vi nhngthnh phn chiu sng khc. Cc xc lp c bn ca vic tnh GI nm trong bng VRay:Indirect Illumination, cc xc lp b sung khc ri rc trong hu ht cc bng cn li caVray. Chng ta s xem xt n ln lt. Vic tnh GI c th bt hoc tt ty trong hp

chn On trong bng VRay: Indirect Illumination.Cc xc lp ca thnh phn chiu sng th t caustic hiu ng quang t nm trong

bng VRay: Caustic VRay: System (Object settings Light settings).

Nh vy, Vray c cu trc modul r rng, cho php bt hoc tt ca thnh phn nyhay thnh phn kia ca s chiu sng khng ph thuc vo cc phn cn li, iu ny tinli cho vic xc lp cc thng s. Tip theo ta s ch xem st chi tit chiu sng khuch tnkhng trc tip (GI)

Cc xc lp c bn ca GI.

tnh ch Indirect Illumination VRay cung cp 3 phng php c bn:


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Tnh trc tip - Direct computation; Irradiance map; Photon map (Global photon map).

C th thy c im ca cc cch tnh l chia cc dng khuch tn phn x ra lm 2

- Khuch tn bt ra ln th nht (nh sng u tin i n mt b mt no , khuch tnmt cch phn x t ch 1 ln ri sau i vo im cn tnh sng) v cc loi khuchtn cn li (nh sng, cho ti khi n im cn tnh sng phn x bi cc b mt cakhung cnh 2 ln hoc nhiu hn th). tng ca vic chia trn n lin quan n sch trng ng gp ca chnh ln khuch tn u tin ca phn x ( ln bt ln khuch tnu tin ca photon), s ng gp ca cc ln cn li s nhanh chng tt theo chiu tngca s ln phn x. tnh 2 loi ny bt c th dng 4 b kt hp khc nhau ca 3phng php tnh trn

Tnh trc tip - Direct computation cho ln bt ln khuch tn u tin v tnh trctip - direct computation (direct+direct) hay photon map (direct +photon) cho cc ln bt

ln sau; Irradiance map cho ln u tin bt ln v tnh trc tip (irr_map+direct) hay

photon map cho cc ln bt ln sau (irr_map+photon).


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.02-04. Ch c chiu sng trc tip v mt ln khuch tn phn x (ln khuch tnbt ln u tin - first diffuse bounces)


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Hnh.02-05. Chiu sng trc tip v tt c cc ln khuch tn phnx, c tnh bng phng php irradiance map cho ln bt ln khuchtn u tin v phng php photon map cho cc ln bt ln khuch tntip theo.


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Hnh.02-05a. Ch c s bt ln khuch tn u tin ( S phn x quali u tin ), c tnh bng phng php irradiance map. thy hnhnh ny c th tnh s chiu sng trc tip v GI vi first diffuse bounces- on, secondary bounces - off v lu irradiance map tnh vo file. Sau tt tt c cc vt th ca khung cnh ra khi s chiu sng trc tip vrender vi irradiance map c load t file.


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Hnh.02-05b. Cn bn thn Photon map c thy nh th ny. thy n ta tt cc vt th ra khi s chiu sng trc tip v tnh firstdiffuse bounces>Global photon map, secondary bounces - off.


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Hnh.02-05c. Photon map v nh sng trc tip, khng c s bt ln phn x th nht

Chiu sng trc tip - Direct computation (DC) dng tnh s chiu sng khuchtn bng phng php Monter Carlo. Tn khc ca phng php ny l Th lc. Khitnh direct+direct cho mi im mt na bn cu c kch thc n v s c xy dng vvic ly samples ca hm di tch phn s c tin hnh ( S lng samples c biudin trong xc lp Subdivs ca nhm First diffuse bounces>Direct computation), m phnct li ca n l phn khuch tn BRDF. Vic ly samples BRDF l s la chn ngunhin mt trong cc gi tr c th ca n, iu tng ng vi vic chn mt hng cth (gc) chiu xung ca nh sng. Theo hng tia d s d ti giao im mi vi b

mt gn nht. Ti im mi s chiu sng trc tip ca n s c tnh ( s l s bt lnphn x u tin) v qu trnh tnh cc ln phn x tip theo cn phi lp li - xy dngbn cu ( hoc c hnh cu cho b mt trong sut), ly samples theo s lng subdivs canhm Secondary bounces>direct computation, tia d mi s d nh th tip cho n khi tc Depth su ca tia d. Bi v s phn x qua li s nhanh chng tt i cng vi sgia tng s ln phn x, thm mt yu t hn ch s lng samples v su tia d, ngoiDepth, l QMC Sampler vi importance sampling v early termination.


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Tnh bng th lc thu c kt qu v s phn b na bng (phn chuyn bng) rtchnh xc hon ton khng b gin on. Nhng thc s rt lu. V d, nu chn Subdivsbng 50 cho c 2 loi bt ln phn x, th s tia samples cho mi im s l 2500, tc l sc 2500 im mi, m ti mi im s li tin hnh d 2500 tia ca chng, v snhn c 2500 im na, c th qu trnh tip din trong khi xc lp QMC vn cho php.

Qu trnh rt nhanh chng c tnh cht nh mt dng thc l, v tt c s lng khng ltia DC s phi c tnh nghim tc v hon thin. S lng samples ca s ny bt thcp ca Vray theo mc nh l 1 tia, n c v hon ton cho kt qu tt cho phn lntrng hp v gim nh r rt khi lng tnh. Ngoi chnh xc tnh na bng cao vtc chm, nhc im ca DC cn l s nhiu, iu lin quan n vic tnh ton cthc hin ring r cho tng im. trnh nhiu ch c 1 phng php nng s lng tiasamples (Subdivs), iu khng r l khng tt cho thi gian tnh ton. V th, direct+directcomputation kh t c s dng trong thc t v ch yu l cho cc hnh reference, gipnhn bit cn phn b nh sng th cp trong khung cnh nh th no ( trong trng hp s nhiu lon khng cn quan tm).

Trong trng hp dng direct +photon, tia d t im cn tnh ch d ti b mt gnnht, ni s tnh s chiu sng trc tip cn s chiu sng t cc ln phn x sau s cnh gi bng mt ca photon map ti im giao trong gii hn ca bn knh cho trc (thng s Search distance ca photon map). Phng php ny nhanh hn phng php trcv c th cn chnh xc hn khi photon map c mt cao.

Cn c thm mt phng php s dng photon map la chn (d on) nhnghng ca DC, cung cp ng gp ng k vo tnh ton. Thc ra, chng nn t chysamples vo khng gian xung quanh nu bit theo hng no cc photon chuyn ng!?Tic rng Vray khng s dng mo ny.

Irradiance map

S khc bit ca phng php irradiance map so vi direct computation l ch,tnh ton c thc hin khng phi cho tt c cc im ca hnh m ch mt t trong s .S chiu sng ca cc im cn li c ni suy theo s chiu sng c tnh ca ccim gn nht (phng php ny c gi l ng dc gradient sng) trong gii hnc cho bi thng s Interp. Samples ca nhm First bounces>Irradiance map. iu cho php tnh sng ca nhng ch thc s cn thit trong khung cnh 3 chiu trong vngc nhng thay i ng k v chiu sng hay b mt hnh hc, v

, - , v t bng gn ng cho nhng b mt phng v c chiusng u.

S tuyn chn cc im tnh v lu trong irradiance map din ra theo tng bc,bt u t phn gii thp nht ca hnh ti phn gii cao nht. phn gii thp nhtc xc nh bi thng s Min. Rate; cao nht - Max. rate ca nhm thng s First


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diffuse bounces>Irradiance Map, gi ca cc thng s ny l s m ca c s 2. Nh thgi tr -2 ng vi cn 0 ng vi 1. Vic tnh irradiance map c thc hin nhiu ln,mi ln chnh xc hn, cung cp cht lng cao hn. V d, nu Min. Rate = -3, cn Max.Rate = 0, php tnh irradiance map s thc hin 4 ln (-3, -2, -1, 0). phn gii gc l phn gii ca hnh cn tnh, c lm nh i tng ng vi cc ln tnh. Vi -3 trong ln

tnh u tin ch thc hin tnh cho 8 im 1 ln. Trong bc tip theo, cc im xungquanh s c so snh vi nhau v s chiu sng. Nu s khc nhau v chiu sng ca ccim, php tuyn ca chng hay vng khng gian gn vt th ln hn 1 gi tr ngng nhtnh, t mi nhm s chn ra v tnh thm cc im b sung

Gi tr ngng cho s chiu sng ( mu sc) c biu th trong thng s Clr. thresh,cho php tuyn - trong Nrm. thresh, cho v tr khng gian gn k - trong Dist. thresh. Saukhi tt c cc bc c thc hin, kt qu tnh ton c th c lu vo file. chnh lbn chiu sng - irradiance map. Do lu tr kt qu tnh vo file, phng phpirradiance map cn c gi l phng php lu tr. Sau mt lot bc render cui sc thc hin cho phn gii gc, trong s chiu sng cc im tnh s c ly

t irradiance map, cn ca nhng im khc s c ni suy bng ng dc theo cc gitr tnh. bc render cui nhng im b sung c th s c tnh qu trnh dovic thit lp supersampling kch hot. Supersampling c nhng gi tr ngng o sngca mnh, c th khng trng vi Clr. thresh, v nu chng nh hn nhng php tnh thms c thc hin cho mt vi im

T im lu cui cng c th rt ra kt lun rng vic thit lp supersampling cth c lm n gin qu trnh thit lp cho irradiance map tng tc tnh ton vthit lp vi yu cu cht lng cao hn sau khi tnh v lu irradiance map, ngay trc khitin hnh render cui. l im khc vi direct computation, cc thit lp chosupersampling chng cn c thc hin trc c khi bt u tnh ton. Nh vy irradiance

map+photon map c s mm do cao nht trong quan h vi supersampling n c thc thay i m khng cn phi tnh li irradiance map cng nh photon map, iu chophp cc php th vi t s tn km sng mu hn vi thit lp supersampling

Kt lun thc tin th 2 cp n s ph thuc ca cc gi tr Min. rate Max. ratevo c nh cn tnh khi tng c nh cc gi tr ny c th c gim i v ngc li. Vd, nu cp gi tr Min. rate = -3 Max. rate = 0 lm vic tt cho nh 800x600 pixel th chonh c kch thc 1200x1024 hon ton c th dng Min. rate = -4 Max. rate = -1, v cnh cao hn cc gi tr ny cn c th h xung na. Trong quan h vi vic khi tng cnh s im cn tnh cng tng suy ra cng mt vng ca khung cnh 3 chiu s c biudin bng mt s lng ln pixel

Bn thn vic tnh sng ca cc im c thc hin tng t nh direct computation ly samples ca na bn cu, tm giao im, tnh s chiu sng trc tip, nu cho nhngs ny bt th cp dng direct computation nhng bn cu mi s c xy dng, nudng photon map s nh gi s chiu sng theo mt photon. Ni chung nh bnhthng. Nhng c mt c im quan trng ca qu trnh tnh irradiance map v firstdiffuse bounce trong tng th; giai on tnh s bt ln khc x u tin din ra qu trnhkt ni ( c - ha trn, kt hp) s chiu sng trc tip cng nh s chiu sng secondary


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bounces. l c im ca Vray. N khng lu tr cc thnh phn chiu sng ring bit,tnh s bt ln u tin da trn kt qu tnh ton chiu sng trc tip v cc s phn x quali khc v kt qu c lu vo file. V d cho s chiu sng trc tip khng c lu trbi bn thn irradiance map, c th bt hoc tt th s phn x qua li nhiu ln sau tnhton c c gi tr ca n. Tc l nu irradiance map tnh c k n photon map v

lu vo file cho cc tnh ton sau , th vic load photon map t file cng nh tnhsecondary bounces c th b qua m khng lm nh hng g n kt qu tnh cui cng.Mt v d khc. Tnh irradiance map khng c secondary bounces v lu vo file. Sau tnh photon map v cng lu vo file. By gi nu nh render vi irradiance map load tfile cho first diffuse bounce, cn secondary bounces vi photon map ghi v tnh sng thvic cng gp nh sng s khng xy ra. Chng ta s ch nhn thy irradiance map v schiu sng trc tip. c im ny ca vic tnh GI trong VRay c nhng mt tch cc can kch thc ca irradiance map nh hn nhiu ln so vi photon map . V c imnu trn cn cho php chng ta s dng ch irradiance map cho cc tnh ton sau nu n c tnh trc c k n photon map v qun i bn photon nhiu MB

Phng php tnh irradiance map thc hin nhanh hn nhiu so vi directcomputation v khng c tn tht no v cht lng hnh nh. V th n l c bn tnhs bt ln khuch tn u tin. Tnh tip hp (adaptive) theo cc im chn trc l mtkhm ph rt th v ca Vray v l u vit thc s ca n. Bi v tnh GI bng irradiancemap + photon map trong VRay tng t vi tnh GI trong mental ray bng s kt hp caphoton map v final gathering. Nhng mt khc, final gathering, khc vi irradiance map,chn cc im tnh tri u theo gi tr bn knh cho sn khng tnh n nhng thay iv mu sc v hnh hc. V th nhn c kt qu cht lng tng ng viirradiance map , final gathering cn dng mt s im ln hn, m iu cngha l thc hin php tnh chm hn

V thi gian render, direct+direct s l chm nht, direct+photon map v irradiancemap + direct s cnh tranh nhau v thi gian, irradiance map + photon map phng phptnh nhanh nht m bo cht lng hnh nh trong nguyn l mang tnh vt l hon thinca photon map. Vi th chnh s kt hp ny c s dng nhiu nht trong thc t. Nhngkhng loi tr ngoi l. V d in hnh tnh sng m bng photon map. V photon rt tdo s tp trung ca cc ngun sng (m m), c th cn n rt nhiu thi gian nhtnhnh chng. V d khc khng c thnh phn khuch tn ca vt liu. Trong trng hp tnh photon map c th tr thnh mt qu trnh v tn khng kt qu bi v photon mapch c xy dng cho b mt c nh sng khuch tn bng 0. Thm mt vd in hnhna tnh khng gian m vi Skylight. Trong v d cui cng c th sa cha bngcch t ng li cc ngun sng.

By gi ta s xem st cc thng s ca maps - irradiance v photon.

Bn Photon (Photon map)

tng photon map (PM) n gin t ngun sng nh sng theo tt c cc hngchia nng lng nh sng photon. Mi mt hng phng (d ) ti khi va chm vo vtth gn nht ca khung cnh v xy ra tng tc ca photon vi b mt. Kt qu ca


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ca tng tc c lu vo mt b c s d liu c bit, chnh l photon map. Tng tcc hiu l photon c th b hp th bi b mt, phn x ton phn hay khuch tn t nhay i qua b mt trong sut ng theo nh lut phn x v khc x nh sng. Hin tngno s xy ra, ph thuc trc ht vo tnh cht ca b mt (tnh cht v h s khuch tn,phn x hay trong sut ca cc vt liu), th 2 l ph thuc vo kt qu ca "bn quay

Rulet kiu Nga"!!!.Bn quay Rulet kiu Nga my m ngu nhin, s dng tng cc h s phn x

khuch tn, phn x ton phn v h s trong sut. V xc sut lun lun hng ti 1 nntng 3 h s cng khng c vt qua 1. Chnh iu m bo thng s Energypreservation mode ca vt liu VRay (trong cho RGB cho rng 0-255 tng ng vikhong 0-1) v c l chnh v th photon map ca Vray ch c th to cho vt liu loiVRayMtl. Bn cht ca "bn quay Rulet kiu Nga" h s ny hay h s kia cng ln thxc sut hin tng tng ng vi n sy ra cng cao - hp th phn x hay khc x.

Sau tng tc, photon d theo hng mi ti b mt tip theo, ni qu trnh s lp li.

su tia d trong Vray c cho bi thng s Bounces trong bng VRay: Global Photonmap. Khi t ti su cho trc ( s ln photon tng tc vi cc b mt), s d caphoton s dng li. Trong cc bn photon ca tt c cc mt m photon tng tc,lu tr cc thng tin v ta va chm, nng lng photon v hng ti ca n. Photonmap cho b mt c to khi v ch khi n c tnh khuch tn khc 0

s dng thnh cng photon map cn c bit hiu cn k mt iu mt photonring l khng th xc nh chnh xc s chiu sng ca im. xc nh chiu sng caim cn mt b s lng nht nh photon, gn vi cc ta im v tng nng lngca chng vi nhng h s khi lng xc nh. Bn knh ca b c cho bi thamSearch distance trong bng VRay: Global Photon map.


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Cc tham s xc lp cho Photon map

Cng nhiu photon c dng cng nh gi chnh xc s chiu sng ca im.Nhng l con dao 2 li nu mt photon thp, b chn nhiu photon s dn tinh sng b m nht Theo mc nh Vray s dng Auto Search dist t tm bn knh ti u

cho b photon, trong Search dist khng c php chnh sa. S dng Auto Search distkhng c khuyn co - nn tt n v dng gi tr ca mnh cho Search dist.

Thm mt phng tin trong b vi s m nht ca nh sng thng s Max.photons, xc nh s photon c thu thp ch khng phi bn knh thu thp. S khc nhaugia Search dist. v Max. photons l ch khi c gi tr Search dist s lng tht ccphoton c thu thp ph thuc vo mt photon ca bn . Khi thit lp gi tr Max.photons s photon thu thp s khng i, m bn knh thu thp s thay i. Khi dng kthp cc thng s s t cnh tranh vi nhau theo nguyn tc ai nhanh hn. Nu ti imca b mt s photon c cho trong Max. Photons c thu thp nhanh hn th gi tr cabn knh s b b qua. Nu trong gii bn knh cho trc khng thu thp s photon

nh vic thu thp s ngng li v gi tr Max. Photons b b qua cn s photon s c xcnh bi mt trong bn knh cho trc bi Search dist.

Trn thc t thng ch s dng 1 trong cc thng s - Search distance (Max.Photons c cho gi tr 0 c ngha l Vray s b qua n). Mt khc nguyn tc cnh tranhc th c s dng thit lp c 2 ch lm vic trong s ph thuc vo mt photonmap. Nu cho gi tr Max. photons bng s photon thu thp c trong gii hn Searchdist. vng c mt photon thp nht ca bn th cho vng c mt cao hn giihn Max. Photons s lm vic, cn cho vng c mt thp gii hn Search distance sc hiu lc. iu dn ti vic bn knh thu thp photon s thay i trong gii hn cakhung cnh ph thuc vo mt photon ca bn , iu s lm gim s dn tri ca cc

mp bng c bit l trong vng c sc trung bnh

Mc d photon map cho ta kt qu vt l chnh xc v s phn b nh sng trongkhung cnh, t c chnh xc cao cn c mt photon dy, tc l cn c s phtra mt s lng photon ln. Tic rng h iu hnh 32 bit hin ti ca cc my tnh c nhnhn ch 2GB cho b nh v cho cc php tnh ghi vo n, iu lm gim nghim trng khnng s dng photon map. Khi no tt c chng ta u lm vic trn h iu hnh 64 bt vi8Terabyte cho tnh ton, c th tt c GI s tnh bng Photon. Con hin ti 8 n 10 triuphp ghi ca photon, ph thuc vo phc tp ca khung cnh, l gii hn tuyt i dunglng ca photon map. Mt ln na trong Vray c s dng mt gii php rt th v, chophp khc phc hn ch v b nh.

Thng s Max. density trong bng VRay: Global Photon map cho php nn d liuca photon map. Vic c thc hin nh sau. Thay v ghi ton b thng tin (nnglng, hng, ta - dung lng cho thng tin ca mt im l 30byte) v mt imtrong bn trc ht s tin hnh phn tch cc im c ghi. Nu nh gn ta photon bay qua c ghi d liu v photon qua trc, nng lng ca photon mich n gin uc cng thm vo nng lng ca photon c lu tr. Nh th, nnglng ca photon c ghi min ph vo photon map. Mc gn c xc nh bi


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thng s Max. Density. N c gi tr c ng ln th bn knh m photon map xem st cngln v xc sut tm thy photon c bay qua cng ln. Nu Max. Density = 0, tt c ccphoton u c lu tr vo bn : s cng gi tr ca photon s khng c, tt c cc ta, hng v nng lng ca mi photon u c ghi li. Nu trong khung cnh s dngn v l mm th gi tr Max. Density = 5 n 10 l hon ton tnh 50 n 100 triu

photon. Vn tn ti mt cu hi photon bay qua c hiu l th no? Ch c ni sgn v ta hay cn tnh n gn v hng v nng lng ca photon?

Mc nn ca photon map khng phi l gii php tt nht cho cht lng cahnh nh. l do mi quan h qua li gia Max. Density v Search dist. tng Max.Density khng trnh khi vic tng bn knh thu th p photon, tc l tng m nht canh sng. Ngoi ra, s cng photon trong gii hn Max. Density cng dn n s m nhtcc chi tit trong chiu sng. V th trn thc t ngi ta c gng gim gi tr ca Max.Density sao cho vn nhn c mt cn thit cho photon map.

Mt kh nng tuyt vi na ca Vray l thut ton s l mp ca cc vt th cho

photon map. V ch mi mt lng photon khng th nhn c ng mp ca cc vt thhay cc vt ni b mt r rng v lin tc, VRay a ra 2 phng php nhn c mpsc nt. Th nht - Convex hull area estimate, tnh gn ng s chiu sng b mt ca ccmp theo photon gn nht. Bn thn tc gi khng mn m lm vi phng php ny, songtrn thc t Convex hull c tha nhn l lm vic kh tt. Convex hull s lm vic tthn nu thng s Max. photons c gi tr khc khng.


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Hnh.02-05d. Photon map vi thng s Convex hull area estimate ang bt. Hy sosnh vi hnh 02-05b thiu nhn mp, gc v cc vt ni

Th hai s dng direct computation tnh sng. iu ny t c bng cch chothng s Retrace threshold khong cch t mp, ni s bt u tnh c Retrace Bounces s lng ln bt ln c tnh cn phi bng gi tr ca thng s Bounces ca photon map.Phng php ny i hi thi gian kh ln v khng phi khi no cng cho kt qu tt.Ngoi ra i khi kt qu tnh mp vn c th hi khc v mu sc so vi cc phn khc cab mt, iu ny i hi phi tinh chnh thng s Retrace Bounces (nh hn ti hn, lnhn sng hn) v cc php tnh b sung. C hai phng php trn u c s dng khrng ri.

Store direct light Cho php lu tr trong photon map thng tin v s chiu sng trctip. Trong cc thut ng v photon map, s va chm u tin ca mi photon vi b mtchnh l s chiu sng trc tip v bn cht (ng nhm vi s va chm khuch tn utin, ci chnh l s va chm th hai ca photon vi b mt). Thng th s ny bt ln u


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tin ca photon trong cc bn khng c lu li trnh s lp li ca php tnh chiusng trc tip.

Hnh.02-05e. Bn photon vi thng s Store direct light c bt.Hy so snh vi hnh 02-05b, c tnh khng c Store direct light vhnh 02-05c, c tnh vi s chiu sng trc tip v photon map

Convert to irradiance map c to ra cho vic tnh sng trung gian theo photonmap. Cho php tng tc tnh irradiance map. S dng s chuyn i tng ng vi"s gip " cc photon ca bn trong vai tr Interp. samples cc vt sng, cn thngs Interp. samples xc nh lng photon gn im cn tnh dng cho vic .


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Hnh.02-05f. Photon map c bt thng s Convert to irradiance map.Hy so snh vi hnh 02-05b, c tnh khng c3 Convert to irradiancemap.


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Hnh 02-05h. Photon map vi Convex hull area estimate - on, Storedirect light - on, Convert to irradiance map - on. Hy so snh vitingh rng cc bn bit l cn so snh vi ci g)

s dng hiu qu photon map (PM)cn phi ch n nhng tnh cht c bn sau can

PM khng ph thuc vo v tr ca camera, vo kch thc ca nh v vo cc xc lpchng rng ca. iu cho php tnh photon map vi mt cn thit ch mt ln, lu vo file

v s dng nhiu ln khng cn tnh li. V d, c th s dng cho thit lp photon map hnh nhc kch thc (c nh) nh vi chng rng ca c xc lp thp. Khng cn tnh li photon mapkhi thay i v tr ca camera v khi thay i c nh. V cn phi tnh li trong tt c cc thay ikhc ca khung cnh: tnh cht ca vt liu v ngun sng, thay i v hnh hc v v tr ca ccvt th - tt c nhng g thay i s chiu sng ca khung cnh.

Thng s Search dist. v Max. photons c th thay i khng cn tnh li photon map. iu cho php tnh photon map vi mt cn thit ch mt ln, lu li vo file, sau thay i cc


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thng s trn v tin hnh render vi photon map c load t file. Rt tin li cho thit lpphoton map. Lm sao iu c th c d hiu, Search dist. V Max. photons ch xc nhlng photon tnh sng v khng thay i photon map.

1. S lng tia photon c cho trong cc tnh cht ca ngun sng trong bng VRaySystems>Lights settings vi du tick ca Generate diffuse v ch ra Diffuse subdivs. S lng tia tia photon s c xc nh bi bnh phng s subdivs, cn thc s - bi cc thng sngng ca QMC. tnh photon map trong cc tnh cht ca cc vt th Object settings cngcn nh du cho Generate GI v Receive GI.

2. Photon map ch c tnh cho cc vt liu Vray. Cho cc dng vt liu khc PMkhng lm vic.

3. Photon map khng lm vic vi ngun sng SkyLight v HDRI. Tnh sng viSkyLight v HDRI ch c th c thc bi irradiance map hoc direct computation.

4. Photon map trong VRay c to ra ch tnh s chiu sng bi s phn x nhiuln ca nh sng, bt u t ln th 2 tr ln. N khng c thit k tnh s bt ln phn x

u tin, tc l s chiu sng t s phn x khuch tn u tin. Cng tc bt photon map chotnh sng ca ln bt ln u tin c trong bng VRay: Indirect Illumination ch dnh cho mcch xc lp bn thn photon map.

ng ngc nhin nhng l thc t l gi tr Bounces ca photon map khng nh hngnhiu n s ln tng tc ca photon vi cc b mt ( v n dung lng ca photon map). Sph thuc ng ra l cng mnh hn qung ng photon i c cng di, cng c nhiuhin tng chng ta phi xem xt. Rt c th l do nh hng ca QMC Sampler. Thay vo, nh thc t cho thy, thng s Multiplier cho Secondary bounces trong bng VRay: Indirectillumination (GI) nh hng su sc ti lng hin tng c nh trong photon map. Hai tnhcht cn c tnh n trong hoch nh v mt ca photon map.

Bt tt Convex hull area estimate, Store direct light v Convert to irradiance map yu cutnh li photon map.

Irradiance Map


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Cc thng s thit lp cho irradiance map

Interpolation type kh nng ni suy s chiu sng ca cc im khng c tnh theocc gi tr chiu sng tnh. Trong trng hp n gin nht s chiu sng ca im c nisuy theo s chiu sng tnh ca cc im gn nht trong s lng c cho bi Calc. Passinterpolation samples. S chiu sng c tng hp li vi h cc s cn bng, ph thuc vokhong cch v hng php tuyn. C tt c 4 dng ni suy (4 phng php khc nhau tnh h s

cn bng), trong s c 3 loi c lin quan n s m nht - Weighted average, Least squaresfit, Least squares with Voronoi weights v mt loi khng c s m nht - Delone triangulation.Theo mc nh VRay dng Least squares fit, nu nh cn loi ni suy khng m nht loiDelone triangulation s c dng, n cung cp hnh nh chnh xc v r rng hn. Mt khc ccloi ni suy trn yu cu tng subdivs irradiance map, bi v khi khng c s m nh t th nhiuca hnh s khng t c lm mm i

Sample lookup phng php chn nhng im tnh sng cho ni suy ca im chotrc. Chng c 3 loi, n gin nht l -Nearest, chn ln lt tt c nhng im nm gn imcho trc. Th hai -Nearest quad-balanced, chia vng gn im ra 4 phn v c gng chn trongmi phn mt lng samples nh nhau, iu thng dn n vic s dng nhng samples khng

phi l tt nht cho ni suy (qu xa). Phng php th ba i hi bc b sung chun b,nhng lm vic khng nhanh hn cc loi khc l my - Precalculated overlapping. N cn bcchun b gi l bn knh nh hng cho mi im tnh. Nhng bn knh nh hng s lnhn ch mt irradiance map nh v ngc li. Sau khi render, s chiu sng ca im sch c ni suy phng php ny cho kt qu cao nht

Randomize samples thng s b sung, nh hng n vic chn cc im trong bctnh nh sng direct computation. Nu du tick c nh, s chn nhng im nm bt qui tc


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vi nhau sao cho p ng nhng tnh ngu nhin nht nh lin h gia v tr ca chng. N cnh hng hu ch ti vic trit tiu mt s loi rng ca, c th l moire.

Check sample visibility Khi bt thng s ny, s ni suy s c thc hin c tnh n

kh nng nhn thy ca cc im. N cho php trnh vic thm nh sng qua nhng mp ngnmng.

Trong sch hng dn ca Vray c mt lot v d trc quan v trnh by ton b nh hngca mi thng s trn n irradiance map v c th l hnh nh. Ti khuyn l nn xem.

Mode Cc ch s dng irradiance map khc nhau. Bucket c li trong render mng,bi v cho mi bucket irradiance map ring s c to ra. i hi cc bc tnh b sung (thigian) cho cc mp buket, mt trong cc phng php tng tc tnh ton tng kch thcbuket. Single frame ban c tnh nhanh hn ng k v ngay l p tc cho c khung hnhnhng ch trn mt my tnh. Cc ch khc dng s dng li irradiance map c tnh

khi thay i v tr ca camera (Incremental add to current map) hay thm ch l dnh cho hotcnh (Multiframe incremental) bn s c tnh khng ton b m ch nhng im khngt ti c.

Khng xt n vic irradiance map km mm hn photon map v thc t l mi thay icc xc l p hay thng s ca khung cnh u i hi tnh li ir. Map, cc chi ph c th gimthiu bng cc ch khc nhau Mode. Irradiance map khng cn tnh li khi thay i cc xcl p antialiasing v trong thit l p Color mapping.

V cc thit l p lin quan n cc gi tr ngng cho cc thng s chn im - Clr. thresh,Nrm. Thresh v Dist. thresh, th bi v VRay s dng mt vi gi tr tru tng (Generic units)

cc gi tr ca chng kh kh lin h vi cc gi tr o thc t ca nh sng, gc php tuyn haykhong cch. Cu cnh ch l nhng Irradiance map preset cho render vi cc mc cht lngkhc nhau. Chn trong danh sch b xc l p ph hp, c th s dng chng nh xut pht im thit l p cc gi tr ngng ca bn thn.

Tnh n tt c nhng c im ni trn c th a ra phng php tnh sng chokhung cnh 3D bng Vray nh sau.

1. Xy dng s chiu sng trc tip. Chn cc dng v s lng ngun sng sao chochng ti a tha mn iu kin t ra, c th l tha mn cc yu cu lm trung thc nh sng.Sau thit l p ch nh sng trc tip bng vic iu chnh cc thng s ca ngun sng.

multiplier, color v nhng ci khc. bc ny cc dng chiu sng khc u tt. Xy dngng nh sng trc tip l m bo cho render p, bi v chnh nh sng trc tip mi l c bnv xc nh.

2. Xc l p v tnh photon map ri lu vo file.3. Xc l p v tnh irradiance map cho first diffuse bounce cng viphoton map c

load t file cho secondary bounces. Sau lu irradiance map tnh vo file.4. Render cui vi xc l p tinh t ca cn bng nh sng bng Vray: Color mapping v


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chn mc kh rng ca cn thit. Trong bc ny dng irradiance map tnh t file.

Trong bi tip theo v d thit l p cho tnh sng mt khung cnh c th theo s nus c xem st

Hn g p li!

Igor_Sivacov([email protected])

Phat hanh 21 thang 7 nm 2004

Dich t ting Nga Raytrace ([email protected]) thang 3 nm 2005
mailto:[email protected]:[email protected]:[email protected]:[email protected]

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