Documentation/Labs/OpenGLFilters

Overview

Here we summarize some efforts for enabling image processing (filtering/smoothing) in VTK/Slicer using OpenGL.

The reason behind this page is trying to coordinate the various projects regarding this subject.

Meetings

9th June 2016

Attended by: Davide Punzo, Jean-Christophe Fillion-Robin, Ken Martin, Utkarsh Ayachit and Robert Maynard

Based on an original idea of Steve Pieper

In order to implement efficient filtering, OpenGL solution seems the best that fits our needs:

• no requirement on external library (CUDA or OpenCL).
• performance boosting is fairly good to allow almost interactive filtering up to volume of ~10^8 voxels.

Source: Finding faint HI structure in and around galaxies: scraping the barrel (submitted)

Use Case

Based on the Steve Pieper implementation of the classes:

vtkOpenGLTextureImage
vtkOpenGLShaderComputation

here an Use case:

https://github.com/Punzo/SlicerAstro/tree/master/AstroSmoothing/Logic
https://www.overleaf.com/read/jbxxsqtctpgv

Full integration in VTK

For a full integration of the openGLfilters pipeline in VTK, it will be ideal to have a general purpose class:

VTKOpenGLImageAlgorithm

this class will have the duty to:

• handle the I/O communication between the vtkImageData and the GPU Texture using fully the VTK shader infrastructure, since the shader infrastructure is already available in VTK (safe binding, automatic versioning, etc... http://www.vtk.org/Wiki/Shader_In_VTK).
• child classes will handle different approach (e.g. multipass/iterative filtering).

Ken Martin provided this structure in VTK: [1]

Next steps

• Talk with Steve and getting his feedback.
• Ken will be very happy to contribute a base class vtkOpenGLImageAlgorithm
  • Timeline: in 2-3 weeks after his vacation
  • Most likely derived from vtkImageAlgorithm, the class will integrate feature from VTK/Rendering/OpenGL/vtkGaussianBlurPass.h to facilitate the use of custom shaders to implement GPU based filters.

Status

• Ken wrote the base class for operation filtering on GPU https://github.com/Kitware/VTK/blob/41fab4e9d7a7b55cd5c7368fee914a74b7bec751/Rendering/OpenGL2/vtkOpenGLImageAlgorithmHelper.h

 and he gave also an example how to use it: https://github.com/Kitware/VTK/blob/3530cb6e8a7992ba1c8dbf5652c2b9d0c21bf4cd/Imaging/OpenGL2/vtkOpenGLImageGradient.h

• An application of the class for filtering can also be found here: https://github.com/Punzo/SlicerAstro/tree/master/vtkOpenGLFilters

References

• Developer_Meetings/20150609
• Developer_Meetings/20150901
• https://github.com/pieper/CommonGL/tree/master/GLFilters
• http://www.vtk.org/Wiki/Shader_In_VTK