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第七章 真实感图形显示 PowerPoint PPT Presentation


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第七章 真实感图形显示. 7.1 线 消 隐. 7.2 面 消 隐. 7.3 光 照 模 型. 7.4 光 线 跟 踪. 7.5 表面图案与纹理. 7.6 颜 色 空 间. 基本概念. 一 . 为什么要消隐 因为计算机图形处理的过程中,不会自动消去隐藏部分,相反会将所有的线和面都显示出来。 所以 :如果想有真实感地显示三维物体,必须在视点确定之后,将对象表面上不可见的点、线、面消去。执行这种功能的算法,称为消隐算法。 例如:. 7.1 线 消 隐. 7.1.1 消隐的分类 线消隐 (Hidden-line)

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第七章 真实感图形显示

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7.1

7.2

7.3

7.4

7.5

7.6


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.


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7.1

  • 7.1.1

  • (Hidden-line)

  • (Hidden-surface)


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7.1

  • k1

  • k h O((kh)2)


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7.1

for ()

{

}


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7.1

  • )

  • mn O(mnkh)


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7.1

for ()

{

}


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7.1

7.1.2

aix+biy+ciz+di=0 i=1, 2, , n (8.1)

(ai, bi, ci)

(8.1)i(li, mi, ni)

(ai, bi, ci)(li, mi, ni)>0


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7.1

  • 8.1.3

  • P1P2


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7.1

    • [0, 1]()


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7.1


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7.2

7.2.1 1


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7.2

2


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7.2

z()

()


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7.2

  • 8.2.2 (Z-buffer)

  • (CB)

  • z --(ZB)

  • z

  • z+Zmax (Z)Z


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7.2

( ZBuffer)

ZBuffer ----

y

z

x

F Buffer

ZBuffer


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7.2

Z-buffer

ZBCBZB(i, j)=ZmaxCB(i, j)=i=1, 2, , mj=1, 2, , n

(i, j)zi, j

zijZB(i, j)ZB(i, j)=zijCB(i, j)=

CB


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7.2

  • (1)ZBCB ZBuffer

    (2)


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7.2

  • 8.2.4

    • Z-bufferZZ


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for ( )

{I(x)

ZZ(x)

for (

{

for

if ( ZZ(x)

{ I(x)

ZZ(x)Z; }

}

}


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7.3

7.3.1

Shading

()

1 RGB

2

RGB

Total_Value=0.30*Value_R+0.59*Value_G+0.11*Value_B

3


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7.3


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7.3

(Diffuse Reflection)(Specular Reflection)

Tp0Tp1


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7.3

7.3.2

  • (Illumination Model)

  • 3


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7.3

  • 1.

  • IsI

  • PLambertBui-Tuong Phong(8.5)

  • EPs=RPcos iIPs+WP(i)cosnsIPs


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7.3

EPs=

RPcos iIPs+WP(i)cosnsIPs

Eps PIPs

RP P

I PNL

Ips

WP(i)P(i)


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7.3

  • WP(i)P(i)W(i)W

W(i)i


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  • nPn

n


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7.3

  • 2.

  • EPt = TPIPb

  • EptP

  • TPP(0~1)

  • IpbP


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7.3

3.

EPd = RPId

EPd-r=RP-rId-rEPd-g=RP-gId-gEPd-b=RP-bId-b


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  • 3PEP

  • EP=EPd+EPs+EPt

  • = RPId+(RPcos i+WPcosns)IPs+TPIpb

  • cos icos s7.3.2)


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7.3

7.3.3

()

GourandPhong


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7.3

Gourand

V


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7.3

Step1:

  • VP1P2PnN1(a1, b1, c1)N2(a2, b2, c2)Nn(an, bn, cn)VnV

nV = (a1+a2++an)i+(b1+b2++bn)j+(c1+c2++cn)k


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7.3

Step2: V

Step3:


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  • (abc)b2ABCD

abc


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Gourand

  • 1

  • 2

  • 3GouraudMach_band

  • Phong


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Gourand


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Phong

    • 1

    • 2

    • 3

    • 4


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7.3

Phong

  • NAN1N2


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1

  • PhongGouraud

  • 1PhongGouraud

  • 2PhongGouraud


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2

  • Phone

Gouraud Phone


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3


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7.3.4


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  • (

S5

S1

S4

S2

S3

I

II

III


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  • 2

  • ii


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3z

  • Williamsz

z

z


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3

  • 1980Whittedraytracing


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  • Wolfgang Heidrich


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Wolfgang Heidrich

1.AB

2.BPQ

3.(0,0,0)(1,1,1)(0.5,0.5,0.5)(1,1,1)AaA

4.Bb

5.c


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7.3.5


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  • Whitted


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Witted

  • Whitted

  • VIl

  • 1Ill

  • 2VRIsl

  • 3VTItl


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Witted

  • Witted

    • IsKs01

    • ItKt0 1

    • IcPhong

    • IsIt

    • IsItVrtrt


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Witted-

  • VRTN

  • Vr

  • t

N

V

1

2

i1=

sin(i2)=1/2sin()

t It


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7.4

  • 8.4.1

  • P0P0P0


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7.4

  • VP0P1P2(8.13)P0P1P2Pn

P0


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7.4

  • ,


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7.4

  • Pi , PiVII=IG+WPIr+TPIt

Pi


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7.4

  • 7.4.2

  • 75%

1


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7.4

(7.23


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7.4

P(x, y, z)V(V1, V2, , Vn)Vi(xi, yi, zi)1in

PVxOyPVViPVi

P=(x, y)Vi=(xi, yi)


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PVPP7.24


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7.4

8.4.3


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7.5

7.5.1

(x, y)(x, y, z)

(x, y, z)

(x, y, z)


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SPSP


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SS

SFESFE

SPSP

PFABP1P1f1/f2PEBCP2P2e1/e2

f1/f2=f1/f2P1e1/e2=e1/e2P2

P1 FP2EP PP


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  • 4SS


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7.5

7.5.2

Blinn1978

S(u, v)

S(u, v)=Q(u, v)+P(u, v)

(8.16)uv


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7.5

NSS(u, v)SuSv

NS = SuSv

=


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7.6

8.6.1

  • (Grassmann H.)3(hue)(saturation)(brightness)(dominant wavelength)(purity)(luminance)

7.28


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7.6

7.6.2 CIE

  • 3

  • (CIE)3XYZ

  • c=xX+yY+zZ

  • :

x y z

x+y+z x+y+z x+y+z

x= y= z=


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7.6

  • x+y+z=1xOyCIE

CIE


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7.6

  • CIE(color gamut)(color range)

CIE


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7.6

8.6.3

  • RGB CMY HSV


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  • (RGB)

RGB


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7.6

  • RGB

RGB


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7.6

  • CMY

  • (Cyan)(Magenta)(Yellow)

CMY


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7.6

  • HSV(Hue, Saturation, Value)

HSV


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7.6

  • HSV


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End of the chapter


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