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Image Fusion

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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  1. Image Fusion In Real-time, on a PC

  2. 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

  3. 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

  4. 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

  5. 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)

  6. 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

  7. 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?

  8. 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

  9. 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

  10. 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?

  11. 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”

  12. 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

  13. 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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