Image-Based Rendering Relief textures

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  (Image-Based Rendering)
• ?????????? ?????? IBR
• ????????? ???????? (relief textures)

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Traditional Rendering

• For photorealism
• Modeling is hard
• Rendering is slow

User input texture maps, survey data
Modeling
Geometry Textures Light sources
Rendering
Images
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Image-Based Rendering

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Image-Based Rendering

• For photorealism
• Fast modeling
• Complexity independent rendering

Images user input range scanners
Modeling
Images depth maps
Rendering
Images
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Traditional vs. Image-based

• Image based computer graphics has three main
  advantages
• Photorealism of produced images
• The speed
• Simple modeling

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Simplest IBR methods. Texture

• Texture - is the simplest of IBR methods.

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Simplest IBR methods. Sprites

• Texture simple planar geometry Sprite
• Sprites are taken from certain camera position
  (sprite camera)

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Simplest IBR methods. Sprites

• No geometry information and...
• Sprites are looking good from view-points close
  to the sprite camera, but awful from others

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3D model rendering distortions

• What are we missing?
• The effect of 3-dimensionality on the screen is a
  combination of two effects perspective
  distortion and parallax
• Sprites are capable of producing perspective
  distortions but they are unable to produce
  correct parallax effect

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Sprites with Depth

• Combine depth and color
• Color texel now is a 3D sample.

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Warping

• Using the samples z-values, image can be
  transformed (or warped), to enchance the image
  descriptive power (realism)

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Planar pinhole camera
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Orthographic camera
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3D point position from a pinhole camera

• One image is not enough to determine location of
  a point in 3D.

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From two cameras

• If we have two cameras, Camera1 and Camera2 with
  different parameters, capturing the same scene
  from different locations, a point can be
  expressed as

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Warping example
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Schematic view
Warping x warp(x)
Depth map
Final view
Parallax, perspective projection, translation
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Relief textures

• Most of modern 3D accelerators can ultimately
  fast render textured triangles
• gt We can use this capability to speed up and
  simplify Image-Based Rendering
• Such an algorithm is called Relief Textures

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Schematic view
Software Hardware
Pre-warping
Texture mapping
Relief textures
Final view
Warped textures
Parallax
Perspective projection, translation
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New warping function

• x warp(x) g(h(x), Poly),
• where
• g(y, Poly) is texture-mapping function and
  usually done in hardware
• h(x) is pre-warpring function

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New warping function (2)

• Prewarping function h(x) after some optimizations
  looks like following
• u2 (u1mud)nud
• v2 (v1mvd)nvd
• Extremely simple, isnt it?

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Two stage warping example
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Two stage warping example (2)
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Filling holes

• This sprite with depth was warped to the new
  viewpoint
• Look how many empty spaces on the women face and
  hair at the picture
• Lets call them holes

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Two classes of holes

• All the holes fall into two classes by its nature
• Resampling problem
• Missing information

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Resampling
Before warping
After warping
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Resampling methods

• Methods to fill the holes
• Inverse warping
• Meshing
• Splatting
• Interpolation

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Splatting

• Draw a little cloud (splat) instead of a pixel in
  desired image. This cloud has to be opaque in its
  center becoming more and more transparent to its
  sides
• Features
• Relatively small computation cost
• Not all the holes are filled

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Interpolation

• Use the fact that u and v are independent from
  each other after pre-warping (two-pass algorithm)
  and linearly interpolate depth and color in the
  intermediate and final images

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Interpolation (2)
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