Thong So Vray

5/21/2018 Thong So Vray

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VRay nh ngha v cch sdngPhn 2: Cch sdng cth

V dvxc lp nh sng cho khung cnh trong VrayTrong phn 1 chng ta tm hiu nhng nguyn l lm vic cbn v chc nng ca mtsthng sxc lp trong Vray. Cn by gihy cng xem xt nhng iu ng dng trnthc tnhthno.

Khung cnhCho cc thit lp ti chn mt khung cnh m cc bn c thtm thy trn Internet ti a chhttp://hdri.cgtechniques.com/~sponza/files. Chn chnh khung cnh do 3 nguyn nhnsau. Thnht khung cnh c to ra c bit th (test) cc khnng ca cc chngtrnh render khac nhau v c trnh by tt ccc dng 3D cbn. Cng trn trang web ctrnh by mt gallery ln cc hnh nh render ca khung cnh ny cho nn c thso snh

kt quca mnh vi nhng ngi khc. Th2, khung cnh c mt tnh cht trung gian khng hn l mt cnh ni tht cng nhkhng phi l mt cnh ngoi tht hon ton. lmt ci sn trong nh, c bao bc kn b!i 4 bc tng. nh sng chiu vo trong t"phatrn qua mt ci ging kh su c to nn t"cc bc tng ca ngi nh. Trong khungcnh c tng 2, vng di ban cng, v nh sng chiu thng vo . Th3 l khung cnhkh ln, khong 40m chiu di. Khung cnh gc c to trong LightWave. Trn trang webcng c version cng vi vt liu tng thch vi 3ds ca n, v chng ta s#lm vic vin. Trong scan-line renderer 3ds max n trng nhthny.


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Hnh 1: Khung cnh c nhn thy thny trong scan-line renderer 3ds max . Thi gianrender vi AthonXP 3200 14 giy.

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Vt liu v hnh khi.

VRay, d sao, cng nhnhng renderer khc, c mt lot cc yu cu vhnh hc ca khungcnh. Hnh khi phi chnh xc, tc l cn phi tun theo nhng i hi bnh thng vdnghnh ng. Hnh khi khng c cha nhng poligon di, mnh (di), cn cc vt ni cn phikhng c bt k$ khe h! no. S t%n ti nhng khe h! l nguyn nhn chnh lt nh sngxuyn qua gc (xut hin hin tng tsng !gc) v vt ni cc bmt. Tt nht nu nhccvt thring bit l nhng m hnh ring bit. V d, khi xy dng phng dng hp nn lm b&ng1 vt thchkhng phi to thnh t"6 vt thhnh hp (box). Khi dng hnh cn sdng cchnh khi xy c, v dnhtng trong thgii thc lun lun c bdy th trong khungcnh "ng cg'ng dng n b&ng mt khng c dy. Bn thn ti lun trnh sdng thao tcboolean to cc l(ca v ca s)b!i v n thng to ra nhng li poligon khng ti u.Phng php tt nht dng hnh ti c th khuyn l lm vic vi Editable poly.

VRay khng i hi vhnh khi nng nhcc chng trnh sdng radiosity, tuy nhin, dnghnh tt l bo m cho vic tnh ton trn n nhanh v khng l(i. V thkim tra v tinh chnhhnh ca khung cnh khi cn l vic lm u tin chu*n bcho render.

Vic chn n vo cho khung cnh l kh quan trng mc d khng phi l b't buc. Khi lmvic vi VRay tin nht l lm vic vi millimetre. l yu cu ca phm vi o cc gi trcaVRay, m vic sdng mm s#tng chnh xc khi lm vic vi n. V d, gi trnhnht cathng sMax. density ca photon map l 0.001 trong ho lng chn. Nhng 0.001 ca 1mv 1mm l hon ton khc nhau. Tt nhin chnh xc cao nh vy ca Max. density chophoton map l +,-./0/11/234506khng xc ng, nhng VRay cn c mt lot nhng thngskhc c gii hn o cng da trn hn vo nhvy. Hn vc dng lun c ththay )i sang hkhc, v d, b&ng cng cRescale World Units 3 ds max. N chc thnhh!ng mnh !ch(khi lng ln cng vic tnh ton s#phi tnh li.

Cng tng tcn ginguyn t'c tng ng gia kch thc ca cc vt thtrong khung cnhv thgii thc. Scn thit ca yu cu bchnh b!i ssdng lut t't dn cng chiu sng theo khong cch trong mi chng trnh render c tnh Global Illumination hinthi.

V ti nh dng photon map nn cn xy dng vt liu. Nhta r, VRay chtnh photonmap cho vt liu VrayMtl. V thcn phi chuyn )i cc vt liu Standard 3ds max cdng trong khung cnh sang dng VrayMtl. Vic chuyn )i vt liu kh d7, ch cn thay )i

dng vt liu sang VrayMtl, m phng tnh diffuse ca vt liu s#c p vo mc tng ng.V mt svt liu gc c bump nn chng s#c thit lp tng ttrong vt liu mi cng vigi trnhvy.

Dung lng ca khung cnh l 66 454 poligon, nhthhon ton chp nhn c. Cc chsvslng hnh hc v vt liu cng quan trng chi ph cho chng l bnhs#khng cdng cho cc mc ch khc tip theo, v d- cho photon map. Cng nhiu bnhtn km chohnh hc v vt liu th cng t bnhcn li cho cc photon v Windows khng thqun lnhiu hn 2 GB bnh- l tt cnhng thtruy cp c cho hthng v chng trnh angchy. Nu khung cnh qu ln render c thl hon ton khng thc hin c. Hoch nh v


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ti u kch thc cho khung cnh cng l mt iu khng km phn quan trng khi chu*n btnhton.

hoch nh cn ly gi trgn vi 1.5 GB (nu bn khng bt %ng thi vi 3ds max thmPhotoshop, Corel Draw, WinAmp, Word v IE :). y l khung cnhvi vt liu c xydng xong.

nh sngV bn thn khung cnh ca chng ta cn c nh sng ban ngy, ti dnh dng 2 ngu%n sng(NS). Mt trong schng m phng mt tri ci cn li nh sng ri rc rng kh'p ca vmtri.

Mt NS bt k$tha mn 3 iu kin sau c thm phng nh sng mt tri

N khng gim cng nh sng theo khong cch

Cc tia sng ca n song song vi nhau;

N c mt trc chiu sng dng mt phn ca mt phng, hnh chnht hay hnh trn.Trong 3 ds max cc yu cu trn gn nh d8n n s la chn NS Target Direct. VrayLightkhng ph hp v khng cung cp cc tia sng song song (yu cu th 2). Thm ch khi t'tIgnore light normal trong thng sca n, mt trc chiu sng s#c dng cu. iu s#d8nti t)n tht cc tia photon, tc l ti vic tng thi gian tnh ton v ch.

Yu cu khng c s t't dn theo khong cch mu thu8n vi nguyn t'c chnh xc vt l vchng ta ang xy dng mt tri. Trong %ha my tnh chc 1 trong scc phng php t'tdn c th- kt quca vic thay )i mt dng nng lng nh sng khi thay )i din tchmt trc chiu sng khi phn bnh sng (tng bn knh hnh cu mt trc chiu sng theotheo thi gian hoc chn gin l theo khong cch t"ngu%n sng). iu d8n n vic t't

dn theo bnh phng khong cch, cn s thay )i cng ch ph thuc vo s thay )ikhong cch (bn knh). Ni vmt tri th khong cch m tia sng i t" ti tri t qu lnso vi sthay )i bn knh mt trc chiu sng trong phm vi tri t. V thsthay )i cngchiu sng trong phm vi cc khong cch trn tri t, ccho l hng trm Km hay vin bi10mm l rt nh. Ni mt cch khc, qucu sng ta ra t"mt tri ti tri t ln ti c9m bmt ca n c thco l phng (hn na vi cs!ln hn rt nhiu so vi vic coi bmt tri tl phng), sthay )i mt nh sng l khng ng kcn cc tia sng l song song. V chnh l schnh xc vt l i vi mt tri nhl mt ngu%n sng. Cc ngu%n sng bnh thngca tri t - hon ton khc. Sthay )i tng i bn knh qucu sng ca chng lc nocng ln, nhn thy c v cn phi tnh n theo qui lut t't dn theo bnh phng khongcch.

Xc lp vtr v cao ca Target Direct trong khung cnh c chn sao cho phn nhn thytrong camera c chiu sng :p nht. Mt trc chiu sng chn l hnh ch nht (LightCone>rectangle) gim nh:schiu tia vo phn :p ca khung cnh sao cho tht thot khichiu cc tia photon l ti thiu. +,-/;,


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nhcung vi n dng mt hnh nh bu tri ph hp vo HDRI. Mt khc nu tnh n vicphoton map khng lm vic vi Skylight v HDRI th thay vo ta dng loi NS VrayLight lthch hp. Tuy th, phng n dng Skylight+HDRI hon ton khng bloi b, chn gin lti y v by giti cha cp n.

Thit lp VrayLight sao cho n c dng chnht tng ng vi kch thc trng pha trn casn trong v t n thp hn mt cht so vi mi. Vtr nhvy hn chti a tht thot photon,

cn schiu sng ngoi mi ca ngi nh s#do VRay Environment m nhim. St't dn v8nbt y khng phi l mt tri.

Hnh. 02. Xc lp VRayLight

Cui cng, thhin mu s'c ca bu tri ta p mu tr'ng cho Environment 3ds max.


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Hnh 03. Khung cnh vi cc ngun sng v camera.

Kch thc render chng ta t l 640J480, Nhthl hon ton cho mc ch xc lp nhsng. Sau khi xc lp ngay trc khi tin hnh render ln cui n cn c thay )i sang kchthc cn thit. Cng cn thng schng rng ca (sau y s#vit t't l AA) ti thiu chfixed rate, subdivs=1, c thcn th hn.

By gi, sau khi btr nh sng, cn thit lp hsnhn (Multiplier) cho cng ca chng.

Thao tc ny cn thc hin qua nhiu bc. u tin chnh sng trc tip. By gita s#lmvic .

T't tnh GI ca VRay v b't u thvi cc gi trcng b&ng cch chrender nh sng trctip v iu chnh ca NS. Cho khung cnh ny ti d"ng li !cc gi trsau: cho Target Direct -3, cho VRayLight - 5 v mu tr'ng cho chai (255, 255, 255). Khi xc lp cng nh sngngay t"ban u ta cng dng cng ciu khin theo lut smtrong VRay: Color mapping,loi - HSV Exponential, Dark Multiplier =1.6, Bright multiplier =1, Affect background off.

Hnh. 04. Khung cnh vi nh sng trc tip strng nhthny.


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Cng ciu khin ny hay !ch(cho php loi i nhng nh sng th"a !nhng ch(qu sng.Trong khung cnh ny ti mun thhin cm gic rc r9ca nh sng ban ngy, do s#th"asng !vng mi khi t c sng cn !cc vng khc. Vn c gii quyt b&ng cngciu khin theo lut smschiu sng. Ni chung scn thit trong kim sot cc ch(th"ahoc thiu sng ny sinh do cc renderer hin giu tnh gi trcng theo schnh xcvt l, iu khng phi lc no cng g'ng gng thc hin c trong m hnh RGB chu*n.

Hnh. 05. Cc thng sca nhm Color mapping gip iu chnh cc cng chiu sng

Tt c c 3 loi iu khin: Linear multiply (ng), Exponential (theo lut s m), HSV

exponential (theo lut smc gili sbo ha mu s'c). Skhc nhau gia Exponential vHSV exponential l !ch(khi bo ha vtng (tone) sau khi tinh chnh c sdng Exponentialhnh nh s# nn hn, kh hn. Trong cc bc cui cng, sau khi tnh photon map virradiance map, c thxut hin yu cu tinh chnh b)sung cho nh sng. Vic hon ton cththc hin b&ng cch tng tv khng phi tnh li bn %.

Thit lp photon map

tnh sng phng php irradiance map + photon map c chn. Lm nh thv nhngnguyn nhn sau: photon map cung cp kt qu nhanh v chnh xc, bn % chiu sng(irradiance map) cng cho tc nhvy v vi thit lp cn thit l cht lng render. Ku vitca phng php ny c xem xt kh kLtrong phn 1.

Chng ta b't u thit lp photon map. Trc , trong bng VRay: Indirect Illumination nhpvo nhng thng snhsau. B6C04B,-


7/21

By gicho first bounce chn phng php Global photon map vi mc ch to ra photon map.Sau y, khi photon map c, ti s#sdng Irradiance map.

Nhp vo gi trSecondary bounces>Multiplier ln nht b&ng 1, v l do kch thc ca khungcnh ln v c nhng phn photon kh bay n. Cng v l do gi trsu tia d photon,Bounces, thit lp b&ng 20 thay cho 10 nhmc nh.

T't Refractive GI caustics v Reflective GI caustics, v ti khng c nh tnh hiu ng caustict"nh sng phn xkhuch tn.

Xc lp quan trng nht by gil slng tia photon t"cc ngu%n sng (subdivs). N cn philn cho hnh nh c cht lng cn thit v nhm bo iu kin tc cao nhtcho cc tnh ton sau. Trong t!ng, mt ca photon map cng cao th bn knh thu thpphoton (Search distance s#vit t't l SD) cng nhv photon map cng cht lng. Thc tcng cn tnh n yu tthi gian tnh ton v hn chca bnhhthng (1,5 GB tr"i phnbnhcho cho hnh hc v vt liu, ch'c bn cn nh?). V th, schn la SD hp l v chnhng mt photon cho n l chin lc ct yu !bc ny.

Phn tch bn thn khung cnh l tiu chu*n cho sla chn gi trSD ph hp. Nu, v dnh,

trong khung cnh c mt svt thquan trng nhn thy tt, ch(chuyn bng ca chng cn thhin th la chn SD l hng vo chng - SD cn phi c gi tr sao cho cung cp c chnh xc chuyn bng dc theo chng. Nu khng c vt thtrng tm, SD c thchn da vokch thc ca khung cnh v n vsdng (SD c o b&ng n vc dng trong khungcnh). V trong khung cnh ca chng ta khng c vt thtrng tm, ti xut SD trong giihn 50-150 mm.s#l ph hp v d"ng li !gi trSD = 100. Sla chn SD cho php ngay lptc xc nh cMax. density (kch thc ca photon map, hay nn ca n, tip theo s#vitt't l - MD), b!i v gia chng c mi lin h. R rng l SD khng thnhhn MD b!i v khi trong gii hn ca SD s#khng c mt photon no. Tc gibi ny khuyn nn gitMlgiaSD v MD trong gii hn 2 n 6, tc l SD=MDx2.6, , chng ta cng s#dng tMl bygi. Nu bn bqua MD tc l cho n gi tr0 (photon map ginguyn dng) th s#khng thnhcng b!i v chng ta cn chiu mt lng kh ln photon, m hn ch ca b nh h thngkhng cho php lm nhth. Chn MD =100/6=15, trong mi tng quan ny gi trca MDlun cn tin ti gi trnhnht c thc. By gichng ta tnh 4 photon map vi cc gi trkhc nhau ca subdivs cho ngu%n sng ln lt l : +,-3000, 5000, 7000 v 8000 subdivs . M(iphoton map tt nhin cn lu vo mt file ring bit.


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Hnh.07 Cc thng sca photon map

Cc thng sca photon map s#khng thay )i, c chng chl gi trca subdivs cho ngu%nsng. Trc khi tnh c tht't thm spht sinh caustic photons ca ngu%n sng v cc vt th(b!i v chng ta khng nh tnh caustic t"nh sng trc tip trong khung cnh ny) v kim tratnh cht ca cc vt thxem Generate GI/Receive GI cho chng c xc lp cha?

Hnh phot_map#3 Photon map s trng nhthny vi 3000 subdivs v nh sng trctip.

Thng k ca photon map:

subdivs 3000 3000 (ngu%n sng thnht v thhai - Target Direct ?VrayLight, mttri v bu tri ca chng ta) ;

chiu ti a: 18 000 000 photon;

Sphoton lu trtrong bn %: 5 635 989;


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Dung lng bnhcn 516.4 MB;

Kch thc file trn Na 315.6 MB.

Hnh. phot_map#5. Photon map vi 5000 subdivs trng nhthny.


subdivs 5000 5000;


Lu trtrong bn %7 788 992;

Dung lng bnhcn 714.1 MB;



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subdivs 7000 7000;



Dung lng bnhcn 827.7MB;

Kch thc file trn Na 505.2 HMB.



subdivs 8000 8000;



Dung lng bnhcn 869.8MB;


D7dng nhn thy l bn %tt nht nhn c vi 128 triu photon (hnh phot_#8). B!i v nc tnh vi thi gian chp nhn c v i hi khng qu nhiu ch(trn Na lu tr. (c l#ti chn n kc3 nm vtrc:), v by giti cng chn n tnh tip. Ni chung, nunhti mun thu h:p gc nhn ca camera th hon c thsdng photon map u tin vi 3000subdivs. Nhng ti mun tm hiu xem ci g s#xy ra !ban cng m ! mt photon maps#l thp nht trong khung cnh v 3000 subdivs c thl khng cho mt nh render chtlng. H/O


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By gi load photon map t" file m n c ghi v tip tc cuc chi vi vic xc lpphoton map. Cthchng ta s#ththay )i SD v vic khng i hi tnh li photon map.

Hnh. sd-10. SD=10. Bn thn bn knh rt tt v cho php chi tit ha hnh nh cao.Nhng tic rng dng bn knh vi mt hin thi ca photon snhn c photonmap rt nhiu, t thit thc sdng.

Hnh. sd-1000. SD=1 met. Nhiu hu nhkhng c, nhng b vo cc chi tit bng rtmnht do bn knh qu ln. Hnh nh trng phng v t th v. V ng l thi gian tnhtng gn ti 30 ln v trong tnh sng thao tc vi mt slng ln photon.


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Hnh. sd-90. Sau mt vi php thb!sung vi bn knh, ti quyt nh d"ng li vi gi trSD=90 . Photon nhn c c nhiu chp nhn c v bn knh thu thp c khnng din tchi tit chiu sng, cn cc vt ni v gc nhn c lin mch, khng nhnthy bdn on. Thi gian tnh photon map c#ng hon ton chp nhn c.

Cho thit lp photon map nhvy c thni l hon tt. Nhng ti mun xut tiu tnthm t thi gian b) sung v thc hin thm mt kL xo, cho php nng cp cht lng caphoton map.

n thi im ny slng photon thu thp Max. photons v8n c t l 0 khng c g nh

h!ng n vic thit lp bn knh thu thp. Chng ta hy cho gi trMax. photons sao cho ntng ng vi slng photon thu thp c trong gii hn SD ca chng ta ti vtr c mt photon thp nht khung cnh. t!ng l cho trong cc vng ca bn %c mt photoncao, schiu sng ca im s# c tnh vi Max. photons. Khi bn knh thu thp s#nhhnso vi gi tr thit lp trong cc xc lp ca SD v s#thay )i phthuc vo mt photonca bn %, t n gi tr thit lp ca gi trSD trong nhng vng c mt thp nht. Nhvy chng ta s#t c cng mt lc 2 mc ch: bn knh thu thp s# thay )i trong sutphoton map v cc vt nhi7u s#mt i su n ca n. Cn do vic gim bn knh thu thpthc t, khnng di7n tchi tit bng s#c nng ln, c bit !vng c s'c trung bnh.

Lm sao tm c gi trMax. photons? Chng ta b't u nng t"ng bc gi trca n t"0vi mt vi bc (v d10 photon) v m(i ln s#tin hnh render hnh. Lc hnh nh !cc vng

c mt photon nhnht (ti v kh chiu sng) khng thay )i na trong khi ta v8n tng )iMax. Photons th gi trlc ca Max. photons s#c ly. Chcn tic l khng c cng cthng trc theo di mt photon map ti mt im bt k$ca khung cnh.


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Hnh. mp-10. Photon map vi Max. photons = 10. Rt nhiu, tip tc tng sphoton thuthp.

Hnh. mp50. Tip tc tng t"ng bc gi tr ca Max. photons, ti d"ng li $ gi tr 50photon. Sau ng%ng 100 photon hnh nh shon ton khng thay !i n&a - ti mi vngca khung cnh t ti gii hn c nh b$i SD. Ch rng cc vt nhiu by gitr$nn t u 'n h(n v khng r nh$hnh sd-90. Sti $cc vt ni v gc c#ng gnnhbin mt hon ton - Convex hull area estimate lm vic.

Mt photon map c xc lp tt l cha kha cho thnh cng v render nhanh. By gi"o chngta chuyn sang phn xc lp irradiance map.

Xc lp Irradiance map

Chng ta li chuyn sang bng VRay: Indirect illumination v trong vai tr tnh khuch tn btln u tin chng ta chn irradiance map. xc lp irradiance map ti chn Irradiance mappreset>High, ngay sau chn - Custom. iu cho php chnh cc xc lp ca preset High


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Hnh 08. Cc xc lp tnh sbt ln u tin ca nh sng bng ph(ng php irradiancemapCc gi trng9ng cho mu s'c, php tuyn, khong cch v slng samples subdivs ta s#ginguyn nhca preset High. Slng subdivs l 50 samples c nghNa l tnh schiu sngkhuch tn ca m(i im s#sdng ti 2500 tia, iu hon ton cho hu ht cc trng hp.Ni chung, pham vi lm vic ca subdivs n&m trong khong 30-120 samples v c th tnghn na khi xut hin nhiu nhi7u trong hnh.Khi c nhi7u cn nghim tc phn tch cc nguyn nhn c thca n b!i v gim gi trng9ngtng ng c thd8n n gii php khng tng. Gi trMin. rate v Max. rate c thhi caov xc lp chng ta dng hnh c kch thc nh(640J480). theo di qu trnh qut ccim c thbt Show calc. phase.By gi ta chuyn sang cc xc lp ca chnh bn % trong bng VRay: Advanced irradiancemap parameters.

)*nh. 09. +,c -,c lp irradiance map


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Thc hin vic thit lp PQc thng s STQ UV n WXn. YTn Interpolation type: Least squares fit.ZW[Vi ra PT P\ thm mt phng Qn na - Delone triangulation, PQi ]# khng UVm m s chiu]Qng ni suy^V STQc vi PQc U[i kTQc, P\ th c _`ng cho Tanh bi Ti s cd eft cao. KhungPnh Pa PTgng ta T[Vn h[Vnianh thng ^a th PTgng ta ]# Least squares fit. Sample lookup(ST nng PTn PQc im j hknh cholTfp ni suy - Precalc'd overlapping, tt nht trong nhngty chn c, chng ta s#nguyn. Thit lp Randomize samples. Check sample visibility ngbt chkhi xut hin vn trong khung cnh lin quan n vic th*m thu nh sng qua b

mt. Trong khung cnh ny vn nhthkhng c, tc l ta s#khng bt.

Calc. pass interpolation samples xc nh slng cc gi trsng tnh cho php ni suy schiu sng ca cc im cha tnh. Gi tr cng cao ng dc cng b&ng v cng nhiu vtnhe. Phm vi gi trcho thng sny nn l 12-25, ta 15. nh du ghi photon map vo file,iu c thhu ch cho cc thao tc tinh chnh b&ng Color map (iu chnh chiu sng theolut sm) v xc lp chng r&ng ca. By gitt c smn sng v c thnhn nt Render !Ti tnh 2 hnh vi 2 xc lp ca photon map - cho Search distance=90, Max. photons=0 v choSearch distance=90, Max. photons=50 (chnh l nhng map ta tnh ! hnh sd90 v hnhmp50). Cn y l nhng g nhn c (kch thc v xc lp AA tm thi ch"a thay )i).

Hnh. irr-1. Hnh nh nhn c bng ph(ng php irradiance map+ photon map viSearch distance=90, Max. photons=0. 640.480, khng c//.

Hnh. irr-2. Hnh nh nhn c bng ph(ng php irradiance map+ photon map 0Search distance=90, Max. photons=50. 640.480, khng c//.


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C nhn ti thch hnh thhai hn v ti s#render ln cui vi chnh n. Ti chiu chnh mus'c mt cht, thay Dark Multiplier t"1.6 thnh 1.4, v t AA:

Hnh.10. Cc xc lp //cho render cui.

V s lm mm AA l mt bc b) sung c lp trong mi quan hvi bc tnh irradiancemap, nn cho xc lp AA, cng nhcho xc lp Color map, bn % lu trong file s#cdng. T"cc blc AA cht lng nht l Catmull-Rom v Mitchell-Netravali. n gin nht lArea. Cc blc xc nh nh h!ng l8n nhau ca cc pixels trong hnh v l kt quca ccnghin cu l thuyt chng rng ca. Cc blc khc ca nhm ny dng cho cc trng hp

c bit, miu tviu c ththy trong ti liu hng d8n ca VRay. Trc khi render, tithay )i c9nh ln 1024J768 v gim gi trMin. rate xung -4, cn Max. rate xung -1. V sim nh tng ln, cht lng irradiance map s#khng bt)n tht. V :

Hnh. cam-1. Render cui, nh t"camera 1.


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Trong khung cnh c mt camera na t trn tng 2. Ti render mt nh t"n v8n dng chnhphoton map t"file v irradiance map c tnh li cho nh mi cng vi cc xc lp tng t.

Hnh. cam-2. Render cui cho cnh t"camera 2. Khu vc ny c mt photon thp nhtkhung cnh. S photon $ y khng vt qu 30 trn din tch thu thp vi Searchdistance =90 mm. Mt php ththc scho photon map.

Hnh.11. Irradiance map, chc sbt ln khuch tn u tin.


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Hnh. 12. Irradiance map, chc sbt ln khuch tn u tin v chiu sng trc tip.

Hnh. 13. Photon map v nh sng trc tip.


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Hnh. cam-3. Thm mt cnh n&a t" camera 1, quay li 180 . V1n photon map vinh&ng xc lp , irradiance map c tnh li.

C xc lp ng cho photon map v irradiance map by gic thly render t"mi im cakhung cnh hay thm ch c thlm hot cnh. Trong trng hp hot cnh cho irradiance mapMode c thdng Multiframe incremental bn % s# c tnh li cho m(i nh mi khnghon ton m chtnh cho nhng im mi, xut hin trong nh.

Hnh. cam-4. Thm mt cnh t"hnh lang trn.

Sdng cng ciu khin theo lut smColor mapping khng phi l phng php duynht sl cc vng qu sng/ti trong hnh. C tha ra thm 1 s%tuy i hi thi gianthit lp cc thng slu nhng c khnng em li hnh nh th vhn.

u tin t cng cc ngu%n sng b&ng phng php thng vi s h( tr ca Colormapping. Nhng trc khi render ln cui ta cng t Color mapping>Type>Linear multiply, G-buffer output channels>Unclamped color v u ra ca hnh nh vo file dng HDRI. Hnh nhtnh b&ng cch ny s#cha ng gi trmu ca cc im nh trong format vi cc gi trcng


20/21

tht ( chkhng phi RGB). Sau file nhn c c thm!li trong HDRShop v dng cckhnng ca n ( hay khnng ca cc plugin, v d- tonemap) chnh sa phm vi ng cahnh thnh phm vi khng gian mu RGB ( ca mn hnh) vi file c lu tr!dng thng.Ku im ca gii php ny l !khnng sdng cc thut ton c bit khc nhau c to racho mc ch iu chnh phm vi ng ca hnh v nhn c hnh nh cui hp d8n hn. Vthm ch a mt hiu ng c bit hay mt im nhn vo hnh, v dnhnh kim trn ccchi tit crm.

Hnh.14. V dthao tac vi HDRI-render trong HDRShop. Vng c s2c trung gian dchchuyn theo hng vpha c s2c sng h(n vi sh3 trca TONEMAP, plugin choHDRShop.

.

Caustic

Hnh. 15.gif Cc thng sxc lp caustic


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Ti s#khng d"ng li chi tit !y vi thm cphn xc lp cc hiu ng caustic, b!i v nuc to thnh b&ng photon map v phng php lm vic vi n ging nhphng php chungthit lp photon map. Ti s#chni vs"khc nhau cn phi tnh ti gia chng. u tin, schiu photon hng vpha vt th, caustic li tnh t"vt th. iu cho php vi gi trkhngln caustic-subdivs cho cc ngu%n sng s#nhn c photon map c mt v cht lng rtcao. Caustic-photon map c tnh v lu trring r#. iu cho php thit lp chng c lpv nhp vo theo yu cu khi render cui. Khi to caustic cng cn ch r&ng trong qu trnh

tnh chtham gia 2 hay mt vi ( nhng cn xa mi c thl ton b) vt thca khung cnh-ngu%n pht caustic v vt nhn (phn x) caustic. Tng ng, vt th- ngu%n pht, trong tnhcht ca n cn bt Generate caustic v t't Receive caustic. Ca vt th phn xcaustic ngcli. Ngu%n pht cn c tnh phn xhoc khc xmnh v IOR ln hn 1, vt nhn ngc li,cn phi l vt chphn xkhuch tn.

Search dist cng nhth caustic cng cht lng v r rng, cng tng tvi Max. photons khimt ca photon mapcao. l tt c.

Kt lun.

VRay rt th vv l mt renderer giu khnng. Ti sc (hy vng l th) miu tnhngthquang trng nht vn 1 trong cc phng php tnh schiu sng ton cnh. Nhng v8ncn rt nhiu vn m vic xem xt chng khng thchvi k do n gin r&ng khng thhiu thu thkhng thhiu thu , nht l trong khun kh)mt bi vit. cn l thao tc vivt liu, v depth of field v motion blur, v lm vic vi cc ngu%n sng, c bit l ngu%n sngphotometric M(i mt chu ng quan tm v tho lun chi tit.

May thay, VRay l chng trnh c sdng rng ri trn thc t, c bit l !ch(chng ti.V thlun c thtm c nhng chuyn gia thc th, nhng ngi c thtrli cu hi cth.Trong mi lin h ny ti rt khuyn vo xem di7n n v VRay trnhttp://www.3dcenter.ru/forum. n tch ly c mt cs!rt ln kin thc theo nhng cuhi c thv sdng chng trnh v bn c th tm thy li gii cho hu ht cc cu hi v

VRay.

Ti mun nhn dp ny trn thnh cm n nhng ngi m kinh nghim v lng nhit huyt vtca h to nn gi trca nhng kin thc c thu thp li.

Thc tVRay c khnng n u c ththy qua cc tc ph*m ca cc master. V !y angni n vic sdng iu luyn, cn phi khng nh mt iu r&ng trnh cc sn ph*m dongi Nga lm trong VRay rt cao. Cc %ng nghip phng ty u nghim tc ni v vic t%nti mt trng phi Visual Rusia .

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