전체 글

(1)

Noise

Wanho Choi (wanochoi.com)

(2)

Signal

• What conveys information (or message)

about the behavior of some phenomenon from a source to an observer

(3)

Frequency

• The number of occurrences of a repeating event ‣ Per unit time: temporal freq.

Per unit length: spatial freq.

time (or length)

(4)

Frequency Domain

Fourier Transform

Spatial domain → Frequency domain

https://ranabasheer.files.wordpress.com/2014/03/ft.gif http://hometheaterhifi.com/wp-content/uploads/2015/05/up-sampling-fig3-sm.jpg

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Colored Noises

https://en.wikipedia.org/wiki/Colors_of_noise

white noise pink noise red noise

brown(ian) noise

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Random Number Generator

Pseudo (=not real) random number generator Unpredictable

DeterministicReproducible

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Random Number Generator

for( int i=0; i<1000; ++i ) {

cout << drand48() << endl; } 0.000985395 0.176643 0.0913306 0.487217 0.454433 0.831292 0.56806 0.0508319 0.0189148 0.298197 . . .

(9)

Good Noise

• 𝒇(𝒑) = 𝑣 (𝒑∈ℝn, 𝑣∈ℝ), (𝑣∈[-1.0,1.0], average=0.0)

Random to the human eye (Not every noise is equal.) Controllable frequency and amplitude

Reproducible (always same results)

Smooth (no sharp feature, C2-continuity) • Correlated (coherency: 𝒑1𝒑2𝒇1𝒇2)

Band-limited (concentrated region in freq. domain.) Invariant (indiscernible translation and rotation)

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Coherent Noises

Value noise Perlin noise Simplex noise • etc. http://libnoise.sourceforge.net/noisegen/index.html

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Lattice & Value Noise

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Lattice & Value Noise

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Lattice & Value Noise

(14)

Interpolation

(15)

Names of Polynomials

degree name formula

1 linear (or monic) ax+b

2 quadratic ax2+bx+c

3 cubic ax3+bx2+cx+d

4 quartic ax4+bx3+cx2+dx+e

5 quintic ax5+bx4+cx3+dx2+ex+f

6 sextic (or hexic) ax6+bx5+cx4+dx3+ex2+fx+g

7 septic ax7+bx6+cx5+dx4+ex3+fx2+gx+h

8 octic ax8+bx7+cx6+dx5+ex4+fx3+gx2+hx+i

9 nonic ax9+bx8+cx7+dx6+ex5+fx4+gx3+hx2+ix+j

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Interpolation

closest neighborhood linear interpolation smooth interpolation http://libnoise.sourceforge.net/noisegen/

(17)

Interpolation

• The flaw is especially apparent when this function

is used to generate a bump-map texture.

http://libnoise.sourceforge.net/noisegen/

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Lattice & Value Noise

A lattice noise acts as a low pass filter. • Noise looks like blurry.

(19)

Infinite Domain

Periodicity by (the first value) = (the last value)

(20)

Value Noise

Divide the n-dimensional space into a lattice. Assign a random value to each lattice point.

Real value range: -1.0 ~ +1.0

Get the noise value of a point by interpolating Two lattice values when n=1.

Four lattice values when n=2. Eight lattice values when n=3.

(21)

Perlin(’s Gradient) Noise

Divide the n-dimensional space into a lattice.

Assign a random gradient to each lattice point. Gradient: unit vector

Lattice value: (gradient vector) • (distance vector) Distance vector: (lattice point) - (query point)

Get the noise value of a point by interpolating Two lattice values when n=1.

Four lattice values when n=2. Eight lattice values when n=3.

(22)

Picking Gradients

• It needs to have enough variation to conceal the

fact that the function if not truly random.

• But, too much variation will cause unpredictable

behavior for the noise function.

• Predefined set of unit vectors (2D:8, 3D:12, 4D:32)

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Why Gradient Noise?

Non-aligned light and dark areas to a lattice

value noise gradient noise

http://libnoise.sourceforge.net/noisegen/ rotation invariant

(24)

Improved Perlin Noise

• Published at SIGGRAPH 2002 after almost 20 years

cubic interpolation quintic interpolation

(2t3+3t2) (6t5-15t4+10t3 )

http://http.developer.nvidia.com/GPUGems/elementLinks/fig05-07.jpg

Original Perlin Noise Improved Perlin Noise

discontinuous

of 2nd order derivative (zero curvature)

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Improved Perlin Noise

cubic interpolation quintic interpolation

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Improved Perlin Noise

cubic interpolation quintic interpolation

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Cons. of Perlin Noise

• Zero at any lattice point

⇒ Value-gradient noise (value+gradient)

• Slow for higher dimensions

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Simplex Noise

Lower computational complexity Linear dimensional scalibility

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Simplex

• A simplest polygon tessellating n-D space • A hyper-tetrahedron with n+1 corners

1D: line segment 2D: triangle

3D: tetrahedron

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Simplex

simplex vertex count hyper-cube vertex count

1D line 2 line 2 2D triangle 3 square 4 3D tetrahedron 4 hexahedron 8 4D pentachoron 5 tesseract 16

O(n)

O(2

n

)

Simplex noise lattice points Perlin noise lattice points

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Simplex Noise

• Step1) Find the simplex including the query point.

(32)

Simplex Noise

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Simplex vs Perlin

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Worley(=Cell) Noise

• Point based approach (But, It also use grid.) • Noise value = the distance to the closest point

(35)

Fractal

If you look at things in nature, they look like fractals.

Various level of details in a mountain

Large variations (mountains)

Medium variations (hills)

Small variations (boulders)

Tiny variations (stones)

. . .

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Fractal

Frequency: the number of cycles in unit length Amplitude: the maximum absolute value

Octave: successive coherent-noises Lacunarity: scale factor of frequency

Persistence(or gain): scale factor of amplitude

float value = 0.f;

for( int i=0;i<numOctaves;++i ) { value += noise( x*f, y*f, z*f ) * a; f *= lacunarity;

a *= persistence; }

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fBm

Fractal Brownian Motion

• The summation of successive octaves of noise,

each with higher frequency and lower amplitude.

http://libnoise.sourceforge.net/noisegen/

+ + +

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fBm

Fractal Brownian Motion

• The summation of successive octaves of noise,

each with higher frequency and lower amplitude.

+ + =

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Procedural Textures

http://lodev.org/cgtutor/randomnoise.html http://devmag.org.za/2009/04/25/perlin-noise/

Play with sin(), cos(), abs(), …

while combining octaves.

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