VRay nh ngha v cch s dng

VRay nh ngha v cch s dngPhn 2: Cch s dng c th V d v xc lp nh sng cho khung cnh trong Vray Trong phn 1 chng ta tm hiu nhng nguyn l lm vic c bn v chc nng ca mt s thng s xc lp trong Vray. Cn by gi hy cng xem xt nhng iu ng dng trn thc t nh th no.

Khung cnh

Cho cc thit lp ti chn mt khung cnh m cc bn c th tm thy trn Internet ti a ch http://hdri.cgtechniques.com/~sponza/files. Chn chnh khung cnh do 3 nguyn nhn sau. Th nht khung cnh c to ra c bit th (test) cc kh nng ca cc chng trnh render khac nhau v c trnh by tt c cc dng 3D c bn. Cng trn trang web c trnh by mt gallery ln cc hnh nh render ca khung cnh ny cho nn c th so snh kt qu ca mnh vi nhng ngi khc. Th 2, khung cnh c mt tnh cht trung gian khng hn l mt cnh ni tht cng nh khng phi l mt cnh ngoi tht hon ton. l mt ci sn trong nh, c bao bc kn bi 4 bc tng. nh sng chiu vo trong t pha trn qua mt ci ging kh su c to nn t cc bc tng ca ngi nh. Trong khung cnh c tng 2, vng di ban cng, v nh sng chiu thng vo . Th 3 l khung cnh kh ln, khong 40m chiu di. Khung cnh gc c to trong LightWave. Trn trang web cng c version cng vi vt liu tng thch vi 3ds ca n, v chng ta s lm vic vi n. Trong scan-line renderer 3ds max n trng nh th ny.

Hnh 1: Khung cnh c nhn thy th ny trong scan-line renderer 3ds max . Thi gian render vi AthonXP 3200 14 giy.----------------------------------------------------------------------------------------

Vt liu v hnh khi.

VRay, d sao, cng nh nhng renderer khc, c mt lot cc yu cu v hnh hc ca khung cnh. Hnh khi phi chnh xc, tc l cn phi tun theo nhng i hi bnh thng v dng hnh ng. Hnh khi khng c cha nhng poligon di, mnh (di), cn cc vt ni cn phi khng c bt k khe h no. S tn ti nhng khe h l nguyn nhn chnh lt nh sng xuyn qua gc (xut hin hin tng t sng gc) v vt ni cc b mt. Tt nht nu nh cc vt th ring bit l nhng m hnh ring bit. V d, khi xy dng phng dng hp nn lm bng 1 vt th ch khng phi to thnh t 6 vt th hnh hp (box). Khi dng hnh cn s dng cc hnh khi xy c, v d nh tng trong th gii thc lun lun c b dy th trong khung cnh ng c gng dng n bng mt khng c dy. Bn thn ti lun trnh s dng thao tc boolean to cc l ca v ca s bi 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 v hnh khi nng nh cc chng trnh s dng radiosity, tuy nhin, dng hnh tt l bo m cho vic tnh ton trn n nhanh v khng li. V th kim tra v tinh chnh hnh ca khung cnh khi cn l vic lm u tin chun b cho render.

Vic chn n v o cho khung cnh l kh quan trng mc d khng phi l bt buc. Khi lm vic vi VRay tin nht l lm vic vi millimetre. l yu cu ca phm vi o cc gi tr ca VRay, m vic s dng mm s tng chnh xc khi lm vic vi n. V d, gi tr nh nht ca thng s Max. density ca photon map l 0.001 trong h o lng chn. Nhng 0.001 ca 1m v 1mm l hon ton khc nhau. Tt nhin chnh xc cao nh vy ca Max. density cho photon map l khng xc ng, nhng VRay cn c mt lot nhng thng s khc c gii hn o cng da trn h n v o nh vy. H n v c dng lun c th thay i sang h khc, v d, bng cng c Rescale World Units 3 ds max. N ch c th nh hng mnh ch khi lng ln cng vic tnh ton s phi tnh li. Cng tng t cn gi nguyn tc tng ng gia kch thc ca cc vt th trong khung cnh v th gii thc. S cn thit ca yu cu b ch nh bi s s dng lut tt dn cng chiu sng theo khong cch trong mi chng trnh render c tnh Global Illumination hin thi.

V ti nh dng photon map nn cn xy dng vt liu. Nh ta r, VRay ch tnh photon map cho vt liu VrayMtl. V th cn phi chuyn i cc vt liu Standard 3ds max c dng trong khung cnh sang dng VrayMtl. Vic chuyn i vt liu kh d, 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 s vt liu gc c bump nn chng s c thit lp tng t trong vt liu mi cng vi gi tr nh vy.

Dung lng ca khung cnh l 66 454 poligon, nh th hon ton chp nhn c. Cc ch s v s lng hnh hc v vt liu cng quan trng chi ph cho chng l b nh s khng c dng cho cc mc ch khc tip theo, v d - cho photon map. Cng nhiu b nh tn km cho hnh hc v vt liu th cng t b nh cn li cho cc photon v Windows khng th qun l nhiu hn 2 GB b nh - l tt c nhng th truy cp c cho h thng v chng trnh ang chy. Nu khung cnh qu ln render c th l hon ton khng thc hin c. Hoch nh v ti u kch thc cho khung cnh cng l mt iu khng km phn quan trng khi chun b tnh ton.

hoch nh cn ly gi tr gn vi 1.5 GB (nu bn khng bt ng thi vi 3ds max thm Photoshop, Corel Draw, WinAmp, Word v IE :). y l khung cnh vi vt liu c xy dng xong.

nh sngV bn thn khung cnh ca chng ta cn c nh sng ban ngy, ti d nh dng 2 ngun sng (NS). Mt trong s chng m phng mt tri ci cn li nh sng ri rc rng khp ca vm tri.

Mt NS bt k tha mn 3 iu kin sau c th m 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 ch nht hay hnh trn.

Trong 3 ds max cc yu cu trn gn nh dn n s la chn NS Target Direct. VrayLight khng ph hp v khng cung cp cc tia sng song song (yu cu th 2). Thm ch khi tt Ignore light normal trong thng s ca n, mt trc chiu sng s c dng cu. iu s dn ti tn tht cc tia photon, tc l ti vic tng thi gian tnh ton v ch.

Yu cu khng c s tt dn theo khong cch mu thun vi nguyn tc chnh xc vt l v chng ta ang xy dng mt tri. Trong ha my tnh ch c 1 trong s cc phng php tt dn c th - kt qu ca vic thay i mt dng nng lng nh sng khi thay i din tch mt trc chiu sng khi phn b nh sng (tng bn knh hnh cu mt trc chiu sng theo theo thi gian hoc ch n gin l theo khong cch t ngun sng). iu dn n vic tt dn theo bnh phng khong cch, cn s thay i cng ch ph thuc vo s thay i khong cch (bn knh). Ni v mt tri th khong cch m tia sng i t ti tri t qu ln so vi s thay i bn knh mt trc chiu sng trong phm vi tri t. V th s thay i cng chiu sng trong phm vi cc khong cch trn tri t, c cho l hng trm Km hay vin bi 10mm l rt nh. Ni mt cch khc, qu cu sng ta ra t mt tri ti tri t ln ti c m b mt ca n c th co l phng (hn na vi c s ln hn rt nhiu so vi vic coi b mt tri t l phng), s thay i mt nh sng l khng ng k cn cc tia sng l song song. V chnh l s chnh xc vt l i vi mt tri nh l mt ngun sng. Cc ngun sng bnh thng ca tri t - hon ton khc. S thay i tng i bn knh qu cu sng ca chng lc no cng ln, nhn thy c v cn phi tnh n theo qui lut tt dn theo bnh phng khong cch.

Xc lp v tr v cao ca Target Direct trong khung cnh c chn sao cho phn nhn thy trong camera c chiu sng p nht. Mt trc chiu sng chn l hnh ch nht (Light Cone>rectangle) gim nh s chiu tia vo phn p ca khung cnh sao cho tht thot khi chiu cc tia photon l ti thiu. , . S tt dn tt nhin l chng ta s b (Decay>Type>None). Chn loi bng l VRayShadow vi cc gi tr theo mc nh.

Ngun sng th 2 cn phi m t nh sng ta xung t bu tri v v th nht nh phi l loi khng gian (dng Area). C th chn NS dng Skylight t b NS ca 3ds max, v khng ti nu nh cung vi n dng mt hnh nh bu tri ph hp vo HDRI. Mt khc nu tnh n vic photon map khng lm vic vi Skylight v HDRI th thay vo ta dng loi NS VrayLight l thch hp. Tuy th, phng n dng Skylight+HDRI hon ton khng b loi b, ch n gin l ti y v by gi ti cha cp n.

Thit lp VrayLight sao cho n c dng ch nht tng ng vi kch thc trng pha trn ca sn trong v t n thp hn mt cht so vi mi. V tr nh vy hn ch ti a tht thot photon, cn s chiu sng ngoi mi ca ngi nh s do VRay Environment m nhim. S tt dn vn bt y khng phi l mt tri.

Hnh. 02. Xc lp VRayLight

Cui cng, th hin mu sc ca bu tri ta p mu trng cho Environment 3ds max.

Hnh 03. Khung cnh vi cc ngun sng v camera. Kch thc render chng ta t l 640480, Nh th l hon ton cho mc ch xc lp nh sng. Sau khi xc lp ngay trc khi tin hnh render ln cui n cn c thay i sang kch thc cn thit. Cng cn thng s chng rng ca (sau y s vit tt l AA) ti thiu ch fixed rate, subdivs=1, c th cn th hn.

By gi, sau khi b tr nh sng, cn thit lp h s nhn (Multiplier) cho cng ca chng. Thao tc ny cn thc hin qua nhiu bc. u tin ch nh sng trc tip. By gi ta s lm vic .

Tt tnh GI ca VRay v bt u th vi cc gi tr cng bng cch ch render nh sng trc tip v iu chnh ca NS. Cho khung cnh ny ti dng li cc gi tr sau: cho Target Direct - 3, cho VRayLight - 5 v mu trng cho c hai (255, 255, 255). Khi xc lp cng nh sng ngay t ban u ta cng dng cng c iu khin theo lut s m trong 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 s trng nh th ny. Cng c iu khin ny hay ch cho php loi i nhng nh sng tha nhng ch qu sng. Trong khung cnh ny ti mun th hin cm gic rc r ca nh sng ban ngy, do s tha sng vng mi khi t c sng cn cc vng khc. Vn c gii quyt bng cng c iu khin theo lut s m s chiu sng. Ni chung s cn thit trong kim sot cc ch tha hoc thiu sng ny sinh do cc renderer hin gi u tnh gi tr cng theo s chnh xc vt l, iu khng phi lc no cng gng gng thc hin c trong m hnh RGB chun.

Hnh. 05. Cc thng s ca 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 s m c gi li s bo ha mu sc). S khc nhau gia Exponential v HSV exponential l ch khi bo ha v tng (tone) sau khi tinh chnh c s dng Exponential hnh nh s nn hn, kh hn. Trong cc bc cui cng, sau khi tnh photon map v irradiance map, c th xut hin yu cu tinh chnh b sung cho nh sng. Vic hon ton c th thc hin bng cch tng t v khng phi tnh li bn .

Thit lp photon map

tnh sng phng php irradiance map + photon map c chn. Lm nh th v nhng nguyn nhn sau: photon map cung cp kt qu nhanh v chnh xc, bn chiu sng (irradiance map) cng cho tc nh vy v vi thit lp cn thit l cht lng render. u vit ca phng php ny c xem xt kh k trong phn 1.

Chng ta bt u thit lp photon map. Trc , trong bng VRay: Indirect Illumination nhp vo nhng thng s nh sau. :

Hnh 06. Chn photon map By gi cho first bounce chn phng php Global photon map vi mc ch to ra photon map. Sau y, khi photon map c, ti s s dng Irradiance map.

Nhp vo gi tr Secondary bounces>Multiplier ln nht bng 1, v l do kch thc ca khung cnh ln v c nhng phn photon kh bay n. Cng v l do gi tr su tia d photon, Bounces, thit lp bng 20 thay cho 10 nh mc nh.

Tt Refractive GI caustics v Reflective GI caustics, v ti khng c nh tnh hiu ng caustic t nh sng phn x khuch tn.

Xc lp quan trng nht by gi l s lng tia photon t cc ngun sng (subdivs). N cn phi ln cho hnh nh c cht lng cn thit v nh m bo iu kin tc cao nht cho cc tnh ton sau. Trong tng, mt ca photon map cng cao th bn knh thu thp photon (Search distance s vit tt l SD) cng nh v photon map cng cht lng. Thc t cng cn tnh n yu t thi gian tnh ton v hn ch ca b nh h thng (1,5 GB tr i phn b nh cho cho hnh hc v vt liu, chc bn cn nh?). V th, s chn la SD hp l v chnh ng mt photon cho n l chin lc ct yu bc ny.

Phn tch bn thn khung cnh l tiu chun cho s la chn gi tr SD ph hp. Nu, v d nh, trong khung cnh c mt s vt th quan trng nhn thy tt, ch chuyn bng ca chng cn th hin 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 th trng tm, SD c th chn da vo kch thc ca khung cnh v n v s dng (SD c o bng n v c dng trong khung cnh). V trong khung cnh ca chng ta khng c vt th trng tm, ti xut SD trong gii hn 50-150 mm.s l ph hp v dng li gi tr SD = 100. S la chn SD cho php ngay lp tc xc nh c Max. density (kch thc ca photon map, hay nn ca n, tip theo s vit tt l - MD), bi v gia chng c mi lin h. R rng l SD khng th nh hn MD bi v khi trong gii hn ca SD s khng c mt photon no. Tc gi bi ny khuyn nn gi t l gia SD v MD trong gii hn 2 n 6, tc l SD=MDx2.6, , chng ta cng s dng t l by gi. Nu bn b qua MD tc l cho n gi tr 0 (photon map gi nguyn dng) th s khng thnh cng bi v chng ta cn chiu mt lng kh ln photon, m hn ch ca b nh h thng khng cho php lm nh th. Chn MD =100/6=15, trong mi tng quan ny gi tr ca MD lun cn tin ti gi tr nh nht c th c. By gi chng ta tnh 4 photon map vi cc gi tr khc nhau ca subdivs cho ngun sng ln lt l : 3000, 5000, 7000 v 8000 subdivs . Mi photon map tt nhin cn lu vo mt file ring bit.

Hnh.07 Cc thng s ca photon map Cc thng s ca photon map s khng thay i, c chng ch l gi tr ca subdivs cho ngun sng. Trc khi tnh c th tt thm s pht sinh caustic photons ca ngun sng v cc vt th (bi v chng ta khng nh tnh caustic t nh sng trc tip trong khung cnh ny) v kim tra tnh cht ca cc vt th xem Generate GI/Receive GI cho chng c xc lp cha?

Hnh phot_map#3 Photon map s trng nh th ny vi 3000 subdivs v nh sng trc tip. Thng k ca photon map:

subdivs 3000 3000 (ngun sng th nht v th hai - Target Direct VrayLight, mt tri v bu tri ca chng ta) ;

chiu ti a: 18 000 000 photon;

S photon lu tr trong bn : 5 635 989;

Dung lng b nh cn 516.4 MB;

Kch thc file trn a 315.6 MB.

Hnh. phot_map#5. Photon map vi 5000 subdivs trng nh th ny.

Thng k ca photon map:

subdivs 5000 5000;

chiu ti a: 50 000 000 photon;

Lu tr trong bn 7 788 992;

Dung lng b nh cn 714.1 MB;

Kch thc file trn a 436.1 MB.

Hnh. phot_map#7. Photon map vi 7000 subdivs trng nh th ny.

Thng k ca photon map:

subdivs 7000 7000;

chiu ti a: 98 000000 photon;

Lu tr trong bn 9 023 203;

Dung lng b nh cn 827.7MB;

Kch thc file trn a 505.2 MB.

Hnh. phot_map#8. Photon map vi 8000 subdivs trng nh th ny.

Thng k ca photon map:

subdivs 8000 8000;

chiu ti a: 128 000000 photon;

Lu tr trong bn 9 486 395;

Dung lng b nh cn 869.8MB;

Kch thc file trn a 531.2 MB.

D dng nhn thy l bn tt nht nhn c vi 128 triu photon (hnh phot_#8). Bi v n c tnh vi thi gian chp nhn c v i hi khng qu nhiu ch trn a lu tr. (c l ti chn n k c 3 nm v trc:), v by gi ti cng chn n tnh tip. Ni chung, nu nh ti mun thu hp gc nhn ca camera th hon c th s dng photon map u tin vi 3000 subdivs. Nhng ti mun tm hiu xem ci g s xy ra ban cng m mt photon map s l thp nht trong khung cnh v 3000 subdivs c th l khng cho mt nh render cht lng.

By gi load photon map t file m n c ghi v tip tc cuc chi vi vic xc lp photon map. C th chng ta s th thay 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 s nhn c photon map rt nhiu, t thit thc s dng.

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

Hnh. sd-90. Sau mt vi php th b sung vi bn knh, ti quyt nh dng li vi gi tr SD=90 . Photon nhn c c nhiu chp nhn c v bn knh thu thp c kh nng din t chi tit chiu sng, cn cc vt ni v gc nhn c lin mch, khng nhn thy b dn on. Thi gian tnh photon map cng hon ton chp nhn c. Cho thit lp photon map nh vy c th ni l hon tt. Nhng ti mun xut tiu tn thm t thi gian b sung v thc hin thm mt k xo, cho php nng cp cht lng ca photon map.

n thi im ny s lng photon thu thp Max. photons vn c t l 0 khng c g nh hng n vic thit lp bn knh thu thp. Chng ta hy cho gi tr Max. photons sao cho n tng ng vi s lng photon thu thp c trong gii hn SD ca chng ta ti v tr c mt photon thp nht khung cnh. tng l cho trong cc vng ca bn c mt photon cao, s chiu sng ca im s c tnh vi Max. photons. Khi bn knh thu thp s nh hn so vi gi tr thit lp trong cc xc lp ca SD v s thay i ph thuc vo mt photon ca bn , t n gi tr thit lp ca gi tr SD trong nhng vng c mt thp nht. Nh vy chng ta s t c cng mt lc 2 mc ch: bn knh thu thp s thay i trong sut photon map v cc vt nhiu s mt i s u n ca n. Cn do vic gim bn knh thu thp thc t, kh nng din t chi tit bng s c nng ln, c bit vng c sc trung bnh.

Lm sao tm c gi tr Max. photons? Chng ta bt u nng tng bc gi tr ca n t 0 vi mt vi bc (v d 10 photon) v mi ln s tin hnh render hnh. Lc hnh nh cc vng c mt photon nh nht (ti v kh chiu sng) khng thay i na trong khi ta vn tng i Max. Photons th gi tr lc ca Max. photons s c ly. Ch cn tic l khng c cng c thng trc theo di mt photon map ti mt im bt k ca khung cnh.

Hnh. mp-10. Photon map vi Max. photons = 10. Rt nhiu, tip tc tng s photon thu thp.

Hnh. mp50. Tip tc tng tng bc gi tr ca Max. photons, ti dng li gi tr 50 photon. Sau ngng 100 photon hnh nh s hon ton khng thay i na - ti mi vng ca khung cnh t ti gii hn c nh bi SD. Ch rng cc vt nhiu by gi tr nn t u n hn v khng r nh hnh sd-90. S ti cc vt ni v gc cng gn nh bin 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 gio chng ta 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 bt ln u tin chng ta chn irradiance map. xc lp irradiance map ti chn Irradiance map preset>High, ngay sau chn - Custom. iu cho php chnh cc xc lp ca preset HighHnh 08. Cc xc lp tnh s bt ln u tin ca nh sng bng phng php irradiance map

Cc gi tr ngng cho mu sc, php tuyn, khong cch v s lng samples subdivs ta s gi nguyn nh ca preset High. S lng subdivs l 50 samples c ngha l tnh s chiu sng khuch tn ca mi im s s dng ti 2500 tia, iu hon ton cho hu ht cc trng hp. Ni chung, pham vi lm vic ca subdivs nm trong khong 30-120 samples v c th tng hn na khi xut hin nhiu nhiu trong hnh.

Khi c nhiu cn nghim tc phn tch cc nguyn nhn c th ca n bi v gim gi tr ngng tng ng c th dn n gii php khng tng. Gi tr Min. rate v Max. rate c th hi cao v xc lp chng ta dng hnh c kch thc nh (640480). theo di qu trnh qut cc im c th bt Show calc. phase.

By gi ta chuyn sang cc xc lp ca chnh bn trong bng VRay: Advanced irradiance map parameters.

Hinh. 09. Cac xac lp irradiance map

Thc hin vic thit lp cac thng s kha la n gian. Chon Interpolation type: Least squares fit. Ngoai ra chi co thm mt phng an na - Delone triangulation, cai se khng lam m s chiu sang ni suy va khac vi cac loai khac, co th c dung cho hinh oi hoi s ro net cao. Khung canh cua chung ta hoan toan binh thng vi th chung ta se Least squares fit. Sample lookup (kha nng chon cac im a tinh cho phep ni suy) - Precalc'd overlapping, tt nht trong nhng ty chn c, chng ta s nguyn. Thit lp Randomize samples. Check sample visibility ng bt ch khi xut hin vn trong khung cnh lin quan n vic thm thu nh sng qua b mt. Trong khung cnh ny vn nh th khng c, tc l ta s khng bt.

Calc. pass interpolation samples xc nh s lng cc gi tr sng tnh cho php ni suy s chiu sng ca cc im cha tnh. Gi tr cng cao ng dc cng bng v cng nhiu vt nhe. Phm vi gi tr cho thng s ny nn l 12-25, ta 15. nh du ghi photon map vo file, iu c th hu ch cho cc thao tc tinh chnh bng Color map (iu chnh chiu sng theo lut s m) v xc lp chng rng ca. By gi tt c sn sng v c th nhn nt Render !

Ti tnh 2 hnh vi 2 xc lp ca photon map - cho Search distance=90, Max. photons=0 v cho Search distance=90, Max. photons=50 (chnh l nhng map ta tnh hnh sd90 v hnh mp50). Cn y l nhng g nhn c (kch thc v xc lp AA tm thi cha thay i).

Hnh. irr-1. Hnh nh nhn c bng phng php irradiance map+ photon map vi Search distance=90, Max. photons=0. 640480, khng c .

Hnh. irr-2. Hnh nh nhn c bng phng php irradiance map+ photon map Search distance=90, Max. photons=50. 640480, khng c .

C nhn ti thch hnh th hai hn v ti s render ln cui vi chnh n. Ti ch iu chnh mu sc 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 h vi bc tnh irradiance map, nn cho xc lp AA, cng nh cho xc lp Color map, bn lu trong file s c dng. T cc b lc AA cht lng nht l Catmull-Rom v Mitchell-Netravali. n gin nht l Area. Cc b lc xc nh nh hng ln nhau ca cc pixels trong hnh v l kt qu ca cc nghin cu l thuyt chng rng ca. Cc b lc khc ca nhm ny dng cho cc trng hp c bit, miu t v iu c th thy trong ti liu hng dn ca VRay. Trc khi render, ti thay i c nh ln 1024768 v gim gi tr Min. rate xung -4, cn Max. rate xung -1. V s im nh tng ln, cht lng irradiance map s khng b tn tht. V :

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

Trong khung cnh c mt camera na t trn tng 2. Ti render mt nh t n vn dng chnh photon 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 nht khung cnh. S photon y khng vt qu 30 trn din tch thu thp vi Search distance =90 mm. Mt php th thc s cho photon map.

Hnh.11. Irradiance map, ch c s bt ln khuch tn u tin.

Hnh. 12. Irradiance map, ch c s bt ln khuch tn u tin v chiu sng trc tip.

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

Hnh. cam-3. Thm mt cnh na t camera 1, quay li 180 . Vn photon map vi nhng xc lp , irradiance map c tnh li.

C xc lp ng cho photon map v irradiance map by gi c th ly render t mi im ca khung cnh hay thm ch c th lm hot cnh. Trong trng hp hot cnh cho irradiance map Mode c th dng Multiframe incremental bn s c tnh li cho mi nh mi khng hon ton m ch tnh cho nhng im mi, xut hin trong nh.

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

S dng cng c iu khin theo lut s m Color mapping khng phi l phng php duy nht s l cc vng qu sng/ti trong hnh. C th a ra thm 1 s tuy i hi thi gian thit lp cc thng s lu nhng c kh nng em li hnh nh th v hn.

u tin t cng cc ngun sng bng phng php thng vi s h tr ca Color mapping. 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 nh tnh bng cch ny s cha ng gi tr mu ca cc im nh trong format vi cc gi tr cng tht ( ch khng phi RGB). Sau file nhn c c th m li trong HDRShop v dng cc kh nng ca n ( hay kh nng ca cc plugin, v d - tonemap) chnh sa phm vi ng ca hnh thnh phm vi khng gian mu RGB ( ca mn hnh) vi file c lu tr dng thng. u im ca gii php ny l kh nng s dng cc thut ton c bit khc nhau c to ra cho mc ch iu chnh phm vi ng ca hnh v nhn c hnh nh cui hp dn hn. V thm ch a mt hiu ng c bit hay mt im nhn vo hnh, v d nh nh kim trn cc chi tit crm.

Hnh.14. V d thao tac vi HDRI-render trong HDRShop. Vng c sc trung gian dch chuyn theo hng v pha c sc sng hn vi s h tr ca TONEMAP, plugin cho HDRShop.

.

Caustic

Hnh. 15.gif Cc thng s xc lp caustic

Ti s khng dng li chi tit y vi thm c phn xc lp cc hiu ng caustic, bi v n uc to thnh bng photon map v phng php lm vic vi n ging nh phng php chung thit lp photon map. Ti s ch ni v s khc nhau cn phi tnh ti gia chng. u tin, s chiu photon hng v pha vt th, caustic li tnh t vt th. iu cho php vi gi tr khng ln caustic-subdivs cho cc ngun sng s nhn c photon map c mt v cht lng rt cao. Caustic-photon map c tnh v lu tr ring r. iu cho php thit lp chng c lp v nhp vo theo yu cu khi render cui. Khi to caustic cng cn ch rng trong qu trnh tnh ch tham gia 2 hay mt vi ( nhng cn xa mi c th l ton b) vt th ca khung cnh- ngun pht caustic v vt nhn (phn x) caustic. Tng ng, vt th - ngun pht, trong tnh cht ca n cn bt Generate caustic v tt Receive caustic. Ca vt th phn x caustic ngc li. Ngun pht cn c tnh phn x hoc khc x mnh v IOR ln hn 1, vt nhn ngc li, cn phi l vt ch phn x khuch tn.

Search dist cng nh th caustic cng cht lng v r rng, cng tng t vi Max. photons khi mt ca photon map cao. l tt c.

Kt lun.

VRay rt th v v l mt renderer giu kh nng. Ti sc (hy vng l th) miu t nhng th quang trng nht v n 1 trong cc phng php tnh s chiu sng ton cnh. Nhng vn cn rt nhiu vn m vic xem xt chng khng th ch vi k do n gin rng khng th hiu thu th khng th hiu thu , nht l trong khun kh mt bi vit. cn l thao tc vi vt liu, v depth of field v motion blur, v lm vic vi cc ngun sng, c bit l ngun sng photometric Mi mt ch u ng quan tm v tho lun chi tit.

May thay, VRay l chng trnh c s dng rng ri trn thc t, c bit l ch chng ti. V th lun c th tm c nhng chuyn gia thc th, nhng ngi c th tr li cu hi c th. Trong mi lin h ny ti rt khuyn vo xem din n v VRay trn http://www.3dcenter.ru/forum. tch ly c mt c s rt ln kin thc theo nhng cu hi c th v s dng 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 v t ca h to nn gi tr ca nhng kin thc c thu thp li.

Thc t VRay c kh nng n u c th thy qua cc tc phm ca cc master. V y ang ni n vic s dng iu luyn, cn phi khng nh mt iu rng trnh cc sn phm do ngi Nga lm trong VRay rt cao. Cc ng nghip phng ty u nghim tc ni v vic tn ti mt trng phi Visual Rusia .

Ti xin dng y. Hy cc tc phm ni tip, chng hay hn mi t ng.

: Karba, "" VRay www.3dcenter.ru. VRay + HDRShop.

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