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CHAPTER 12. DISPLAYING IMAGES IN VTK

Draft December 13, 2006

Figure 12.2 is a flowchart illustrating the pipeline for displaying an image slice as a texture mapped onto a rectangular plane. The pipeline is divided into three rows:

  • Top Row (Geometry Pipeline): vtkPlaneSource (generates 2D Plane to map image to) connects to Mapper ( vtkPolyDataMapper ), which connects to vtkActor .
  • Middle Row (Texture Pipeline): Image Source connects to Extract Slice ( vtkExtractVOI ), which connects to Create Texture ( vtkTexture ).
  • Bottom Row (Color Mapping): Generate ( vtkLookupTable for Mapping colors) connects to Create Texture ( vtkTexture ).

The Create Texture filter receives input from both the extracted slice and the lookup table, and its output feeds into the geometry pipeline via vtkActor .

Figure 12.2: The pipeline for displaying an image slice as a texture mapped onto a rectangular plane. The top row is the geometry pipeline which simply displays a bounded plane. The middle row is the texture pipeline for generating the appearance of the rectangle. A colormap (bottom) is added to perform the mapping from image intensity to colors.

12.4 Displaying Texture Mapped Slices

The pipeline for displaying slices as textures mapped onto planes is shown in Figure 12.2. In general there are three parts: (i) We draw the ‘geometry’ by placing a rectangle at the appropriate position. (ii) We generate the source image by extracting the appropriate 2D slice from a potentially 3D image. (iii) We create the texture by combining this 2D image slice with a Colormap and apply it to the geometry.

The first part of the script (script12-2.tcl) is fairly standard: 

lappend auto_path [ file dirname [ info script ]]
package require newname; wm geometry . 200x200

Next we load the image using a StructuredPointsReader , which reads in images stored in the native vtk format. Following this we extract a single slice from the image using the vtkExtractVOI filter (VOI= Volume of Interest). Incidentally, if we wanted to extract a “coronal” slice we could specify $voi SetVOI 0 41 25 25 0 55 , to extract a slice that has constant y-axis. 

set tr [ vtkStructuredPointsReader [ newname::vnewobj ]]
$tr SetFileName brain.vt
$tr Update

set voi [ vtkExtractVOI [ newname::vnewobj ]]
$voi SetInput [ $tr GetOutput ]
$voi SetVOI 0 41 0 47 30 30

The next step is to generate a simple colormap that maps 0 to black and 1 to white. Then a texture ( vtkTexture ) is created which takes two inputs: (i) the image slice – from the output of vtkExtractVOI , and (ii) the colormap.

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