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Image Correction for Immersive Visualization Systems. Alex Timchenko 02/03/2006. Project Background. Immersive Visualization System TAMU TITF Grant 2002 - 2005 NSF Grant - Ongoing Principle Investigators Dr. Frederic Parke Dr. Donald House. Project Purpose.

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project background
Project Background
  • Immersive Visualization System
    • TAMU TITF Grant 2002 - 2005
    • NSF Grant - Ongoing
  • Principle Investigators
    • Dr. Frederic Parke
    • Dr. Donald House
project purpose
Project Purpose
  • Development of a modular low-cost immersive environment
    • Visuals consists of a set of projectors back-projecting images on polygonal facets
    • Have to utilize readily available technology and materials
    • Powerful programming API to facilitate development of new applications for the system
need for coherency
Need for Coherency
  • Temporal coherency
    • Each display must project a part of the world in-sync with the other projectors
    • Achieved through network protocols
  • Spatial coherency
    • Two adjacent facets must display adjacent information with as little of a seam as possible
the problem
The Problem
  • Image alignment on individual projectors

We Want…

We Get…

problems with projectors
Problems with Projectors

The projector is off-axis; lower distance shorter than upper distance

Results in strong vertical perspective distortion

problems with projectors1
Problems with Projectors
  • Perspective distortion
    • Vertical distortion
      • Keystone
    • Horizontal distortion
      • Keystone correction not as common
      • More expensive
    • Keystoning reduces image quality
    • Difficult to manually align projector
problems with projectors2
Problems with Projectors
  • Barrel Distortion
    • Very difficult to manually correct
    • Makes perfect alignment virtually impossible
problems with projectors3
Problems with Projectors
  • Other Problems
    • Non-uniform Intensity
    • Non-uniform Color
    • Color difference between projectors
  • Manual/Mechanical Solution
    • Very difficult to precisely align
    • No way to correct barrel distortion
  • Software based solution
    • Apply a real-time warp to the projected image, allowing the user to control the corners and midpoints of the polygon
  • First approach: Quad-Grid
    • Each edge vertex is moveable
    • Moving the corners corrects perspective distortion
    • Moving the edge points corrects barrel distortion
First approach: Quad-Grid

Good visual results

Difficult to use

Limited to quads

Rendered with OpenGL evaluators

  • Next Approach: Web
    • Improved intuitive interface
    • Applicable to n-sided facets
    • Very simple structure
  • Next Approach: Web
    • Difficult to find centroid
    • Texture “swims” across seams
    • Localized texture effect

Creates slight shear and pinch

Unaffected area


No side-effects

  • Next Approach: N-Grid
    • Places a grid over an n-sided facet
    • Distributes texture difference over a larger area
    • Focuses distortion to corners
    • Structure is difficult to handle
    • OpenGL rendering issues
  • Other approaches?
    • Spring-based meshes
      • Treat interior points as particles
      • Treat edges as springs
      • Spring Stability
      • Return to initial state
gpu rendering
GPU Rendering
  • Instead of relying on OpenGL default texturing, control the warping through the GPU
  • Create a 2D displacement texture
  • Access the displacement texture to get an offset, then access the image with the UV coordinates and the offset
gpu rendering1
GPU Rendering
  • If we can find a displacement map for a mesh, we can use it
  • Requires fairly advanced GPU Hardware









Common Functionality

Parallel Texture Access

Advanced Functionality

Sequential Texture Access

gpu rendering2
GPU Rendering
  • Other advantages
    • Color correction
      • Easy to hue/color shift texel values
    • Brightness correction
      • Easy to adjust the brightness of texels
      • Intensity falloff correction by altering brightness based on some grayscale image
  • Image correction critical to immersive display systems
  • Commodity projectors introduce problems
  • Perspective and barrel distortion are difficult to correct manually
  • Software solutions based on grid structures and real-time image warping produces best results