1 / 17

Real-Time Volume Graphics [05] Transfer Functions

Real-Time Volume Graphics [05] Transfer Functions. Classification. During Classification the user defines the „Look“ of the data. Which parts are transparent? Which parts have which color?. Classification. During Classification the user defines the „Look“ of the data.

damia
Télécharger la présentation

Real-Time Volume Graphics [05] Transfer Functions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Real-Time Volume Graphics[05] Transfer Functions

  2. Classification • During Classification the user defines the „Look“ of the data. • Which parts are transparent? • Which parts have which color?

  3. Classification • During Classification the user defines the „Look“ of the data. • Which parts are transparent? • Which parts have which color? • The user defines a Transfer function. Emission RGB scalar S Transfer Function Absorption A

  4. Classification Real-Time update of the transfer function necessary!!!

  5. Classification

  6. data value data value Pre- vs Post-Interpolative Classification PRE-INTERPOLATIVE POST-INTERPOLATIVE interpolation optical properties optical properties interpolation

  7. GeometryProcessing FragmentOperations TransferFunction Rasterization Pre-Classification • Pre-Classification: Color table is applied before interpolation.(pre-interpolative Transfer function) • A color value is fetched from a tablefor each Voxel • A RGBA Value is determined for each Voxel

  8. Main Memory Graphics Memory skalar value S Scalar Texture AGP /PCIe Texture palette Transfer function Possible Implementations • The best approach: Paletted TexturesStore the scalar volume together with the color table directly in graphics memory. • Hardware-Support necessary! • Low memory consumption • Main Memory (scalar volume can be deleted!) • Graphics Memory (scalar volume + TF) • Low load on memory bus • Scalar volume must be transferred only once! • Only the color table must be re-uploaded on TF change

  9. Pre-Classification Summary • Summary Pre-Classification • Application of the Transfer function before Rasterization • One RGBA Lookup for each Voxel • Different Implementations: • Texture Transfer • Texture Color Tables (paletted textures) • Simple and Efficient • Good for coloring segmented data

  10. FragmentOperations Rasterization GeometryProcessing TransferFunction Post-Classification • Post-Classification: The color table is applied after Interpolation (post-interpolative Transfer function). • A color is fetched from the color table for each Fragment

  11. Post-Classification Texture 0= Scalar field R=G=B=A=Scalar field S RGBA Polygon = T(S) Texture 1 = Transferfunction [Emission RGB, Absorption A] R

  12. CG Implementation //fragment program for post-classification //using 3D textures float4 main (float3 texUV : TEXCOORD0, uniform sampler3D volume_texture, uniform sampler1D transfer_function) : COLOR { float index = tex3D(volume_texture, texUV); float4 result = tex1D(transfer_function, index); return result; }

  13. Quality: Pre- vs. Post-Classification • Comparison of image quality Pre-Classification Post-Classification Same TF, same Resolution, same Sampling Rate

  14. Quality Pre-Classification Post-Classification

  15. Continuous data Discrete data Pre-interpolative TF Pre- vs Post-Classification alpha value Scalar value Transfer Function Transfer Function Supersampling Supersampling Transfer Function Classified data Analytical Solution Post-interpolative TF

  16. Pre-Integrated Classification

  17. When to use which Classification • Pre-Interpolative Classification • If the graphics hardware does not support fragment shaders • For simple segmented volume data visualization • Post-Interpolative Classification • If the transfer function is “smooth” • For good quality and good performance (especially when slicing)

More Related