P1258846336cAfsw

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Krivljenje slike - warping
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Princip 2D krivljenja
Demo
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Krivljenje (Warping)

• Krivljenje (warp) je 2-D geometrijska
  transformacija in ob uporabi na neki sliki tvori
  popaceno sliko
• Dva nacina krivljenja slik- ? Preslikava
  naprej (Forward mapping). ? preslikava nazaj
  (Reverse mapping).

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Krivljenje (Warping)
warp
Destination image
Source image
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Preslikava (mapping)
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Primer preslikave
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Primer preslikave
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Primer preslikave
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Primer krivljenja
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Druge preslikave
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Implementacija krivljenja slike
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Preslikava naprej
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Preslikava naprej
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Preslikava naprej
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Problemi preslikave naprej
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Problemi preslikave naprej
V rezultirajoci sliki lahko pride do lukenj
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Problemi preslikave naprej
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Preslikava nazaj (backward mapping)
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Implementacija krivljenja slike (2)
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Preslikava nazaj
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Problemi preslikave nazaj
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Problemi preslikave nazaj
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Forward and Reverse Mapping

• Forward ? Some pixels in the destination might
  not get painted, and would have to be
  interpolated.
• Reverse ? Every pixel in the destination image
  gets set to something appropriate.

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Ponovno vzorcenje (Resampling)

• Evaluate source image at arbitrary (u, v)
• (u, v) does not usually have integer coordinates
• Some kinds of resampling
• Point resampling
• Triangle filter
• Gaussian filter

Source Image
Destination Image
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Vzorcenje tock (Point Sampling)

• Take value at closest pixel
• int iu trunc(u 0.5)
• int iv trunc(v 0.5)
• dst(x, y) src(iu, iv)
• Simple, but causes aliasing

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Trikotni filter

• Konvolucija s trikotnim filtrom

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Trikotni filter

• Bilinearna interpolacija 4 najbližjih pikslov
• a linear interpolation of src(u1, v2) and
  src(u2, v2)
• b linear interpolation of src(u1, v1) and
  src(u2, v1)
• dst(x, y) linear interpolation of a and b

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Konvolucija z Gaussovim filtrom
Width of Gaussian kernel affects bluriness
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Primerjava metod filtriranja

• Kompromisi
• Aliasing nasproti zamegljevanju
• Hitrost racunanja

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Implementacija krivljenja slike
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Implementacija krivljenja slike
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Primer skaliranje
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Primer vrtenje
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Primer vrtinec (swirl)
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Povzetek krivljenja slik
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Preslikava naprej in nazaj

• In either case, the problem is to determine the
  way in which the pixels in one image should be
  mapped to the pixels in the other image.
• So, we need to specify how each pixel moves
  between the two images.
• This could be done by specifying the mapping for
  a few important pixels.

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2D krivljenje objektov
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2D krivljenje objektov

• The shape modification can also be performed on a
  vertex-basis instead of on a space-basis.
• A displacement for a seed vertex can be specified
  by the user and this displacement can be
  propagated to nearby vertices.
• The displacement can be attenuated as a function
  of the distance that the vertex to be displaced
  is away from the seed vertex.

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2D krivljenje objektov

• The distance function can be chosen to trade-off
  quality of results and computational complexity.
• Minimum number of edges connecting the vertex to
  be displaced from the seed vertex.
• Minimum distance traveled over the surface of the
  object to get from the vertex to be displaced to
  the seed vertex.
• Power functions to control the amount of
  attenuation.
• The user could select the maximum distance at
  which the displacement would have an affect.

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Preslikava tekstur
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Preslikava tekstur