Image fusion
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Image Fusion. In Real-time, on a PC. Goals. Interactive display of volume data in 3D Allow more than one data set Allow fusion of different modalities (e.g. CT+PET) Allow simultaneous display of all data sets. Considerations. Must run on consumer level hardware

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Image Fusion

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Image fusion

Image Fusion

In Real-time, on a PC


Goals

Goals

  • Interactive display of volume data in 3D

    • Allow more than one data set

    • Allow fusion of different modalities (e.g. CT+PET)

    • Allow simultaneous display of all data sets


Considerations

Considerations

  • Must run on consumer level hardware

    • APIs such as OpenGL™ Volumizer already available on High End machines ($$$$$)

    • Must run at interactive frame rates

    • Must allow flexibility in visualization of data


Requirements

Requirements

  • Allow for:

    • Arbitrary viewpoints

    • Arbitrary “slicing” to show internal detail

    • Flexible transfer functions

      • User adjustable for:

        • Colors

        • Transparency

    • Arbitrary mixing of multi modal data sets


Problems

Problems

  • More $$$$ = More flexibility, so:

  • Consumer cards have less than 128 MB of shared memory (texture, frame buffer etc)

  • PCs have more main memory but it is slow

  • Don’t have X units working together

    • Need processing power, (lots of it)


Workarounds

Workarounds

  • Limited memory on video card

    • Roam around a high resolution data set by selecting smaller areas that fit in available memory

      • Still slow, because when the viewpoint moves new data needs to be loaded (from main memory)

    • Down sample data to fit in memory

      • Loss of detail


Workarounds1

Workarounds

  • Compress textures

    • Implementations will allow for a 8:1 compression of textures

    • Will quality be affected? How much?

    • Will it compromise flexibility? How much?

  • Processing power needed

    • Use programmability of newer “GPU”s to leverage available high speed memory

    • Do transfer functions on the GPU? In parallel?


  • Details

    Details

    • Allow user to choose blending between the data sets

      • Assign colors, transparencies and mixing values

      • Each data set must have its own transfer function(s)

    • Registration

      • Not handled


    Rendering

    Rendering

    • How?

      • Volume data Volume textures (3D Textures)

      • “Project” onto 2D screen by overlaying slices

      • Slices are perpendicular to the screen

      • Slices are cut from the volume at fine enough intervals and blended together to produce a single viewpoint image

      • Repeat for different views (rotations/scale) etc


    Rendering1

    Rendering

    • More datasets

      • Could render image for each data set and overlay on top (multipass = slow)

      • Render once, applying both textures at once

        • Limited to 2 textures on most cards

      • Use “shaders” to program the GPU

        • + Very flexible, 2+ textures at once

        • - Flexibility?


    Rendering2

    Rendering

    • Lighting

      • Current rendering mode does not help with lighting

      • Must be done at a lower level

    • Surfaces

      • No real “surfaces” generated, so lighting is hard to do, must be done at the voxel level

      • Lighting at voxel level, will show appearance of “surfaces”


    Conclusions

    Conclusions

    • Limited Memory & Large data sets

    • Want lighting & lack of “surfaces”

    • But we have a programmable GPU to our advantage

      • Dataset manipulation in fast video memory = Faster rendering

    • Alternative rendering methods?

      • Most are CPU bound


    References

    References

    • http://www.opengl.org

    • http://www.sgi.com/software/volumizer/

    • http://www.cs.utah.edu/~jmk/simian/

    • http://www.nvidia.com

    • http://www.ati.com

    • http://www.cla.sc.edu/psyc/faculty/rorden/render.html


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