[vtkusers] greyscale/color rendering

[anast.jm at pg.com]

Chunyan,

The reason your volume renders in color is that you have assigned colors to your
color transfer function. If you make all the rgb values equal (that is r=g=b)
you will get a grayscale rendering

vtkColorTransferFunction::New();
    colorTransferFunction->AddRGBPoint(0.0, 0.0, 0.0, 0.0);
    colorTransferFunction->AddRGBPoint(64.0, 1.0, 0.0, 0.0);  red => 1.0, 1.0,
1.0 white
    colorTransferFunction->AddRGBPoint(128.0, 0.0, 0.0, 1.0); blue => 1.0, 1.0,
1.0 white
    colorTransferFunction->AddRGBPoint(192.0, 0.0, 1.0, 0.0); green => 1.0, 1.0,
1.0 white
    colorTransferFunction->AddRGBPoint(255.0, 0.0, 0.2, 0.0); pale green => 0.2,
0.2, 0.2 light gray

You might want to try a gray ramp if this doesn't look very good

(0.0, 0.0, 0.0, 0.0);
(64.0, 0.2, 0.2, 0.2);
(128.0, 0.4, 0.4, 0.4);
(192.0, 0.7, 1.7, 0.7);
(255.0, 1.0, 1.0, 1.0);

john


                                                                
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From: "Chunyan Jiang" <jiang at TI.FhG.DE>@public.kitware.com on 10/28/2002 11:37
AM CET
                                                                                           
    "Chunyan Jiang" <jiang at TI.FhG.DE>           To:   "VTK-User"                           
                  @public.kitware.com        <vtkusers at public.kitware.com>                 
                                                Cc:    (bcc: John Anast-JM/PGI)            
                                        Subject:      [vtkusers] greyscale/color           
                             Sent by:                                                      
    vtkusers-admin at public.kitware.com                                                      
                  10/28/2002 05:37 AM                                                      
                                                                                           
                                                                                           




Dear VTK friends,
I import the greyscale image data from memery to vtkImageImport, then
transform the vtkImageImport to vtkStructuredPoints by
vtkImageToStructuredPoints. After that I use vtkVolumeRayCastMapper to
render the volume. It works now, however, the greyscale image changes to
color image. How can I render grey image? I attach the code below. Is there
something wrong? Any help is appreciated.

Code:
     vtkImageImport *importer = vtkImageImport::New();
     importer->SetWholeExtent(1,dimensions[0],1,dimensions[1],1,dimensions[2]);
     importer->SetDataExtentToWholeExtent();

     importer->SetDataScalarTypeToUnsignedChar();

     importer->SetDataOrigin(0,0,0);
    importer->SetDataSpacing(1,1,1);
     importer->SetImportVoidPointer(data);//data is unsigned char* that storing
greyscale images data

     vtkStructuredPoints* structPts= vtkStructuredPoints::New();
     vtkImageToStructuredPoints* its=vtkImageToStructuredPoints::New();
     its->SetInput(importer->GetOutput());
     structPts=its->GetOutput();



// Create transfer mapping scalar value to opacity
     vtkPiecewiseFunction *opacityTransferFunction =
vtkPiecewiseFunction::New();
    opacityTransferFunction->AddPoint(20, 0.0);
    opacityTransferFunction->AddPoint(255, 0.2);

// Create transfer mapping scalar value to color
     vtkColorTransferFunction *colorTransferFunction =
vtkColorTransferFunction::New();
    colorTransferFunction->AddRGBPoint(0.0, 0.0, 0.0, 0.0);
    colorTransferFunction->AddRGBPoint(64.0, 1.0, 0.0, 0.0);
    colorTransferFunction->AddRGBPoint(128.0, 0.0, 0.0, 1.0);
    colorTransferFunction->AddRGBPoint(192.0, 0.0, 1.0, 0.0);
    colorTransferFunction->AddRGBPoint(255.0, 0.0, 0.2, 0.0);

// The property describes how the data will look
     vtkVolumeProperty *volumeProperty = vtkVolumeProperty::New();
    volumeProperty->SetColor(colorTransferFunction);
    volumeProperty->SetScalarOpacity(opacityTransferFunction);

// The mapper / ray cast function know how to render the data
     vtkVolumeRayCastCompositeFunction *compositeFunction=
vtkVolumeRayCastCompositeFunction::New();
     vtkVolumeRayCastMapper *volumeMapper=vtkVolumeRayCastMapper::New();
    volumeMapper->SetVolumeRayCastFunction(compositeFunction);

    volumeMapper->SetInput(structPts);//sp reader->GetOutput()

// The volume holds the mapper and the property and can be used to
position/orient the volume
     vtkVolume *volume = vtkVolume::New();
    volume->SetMapper(volumeMapper);
    volume->SetProperty(volumeProperty);


     renderer->AddActor(volume);

  // interact with data
  renWin->Render();

***********************************************************************
Chunyan Jiang, Dipl.-Inform.,
Institut for Telematic
Bahnhofstrasse 30-32, D-54292 Trier, Germany
Phone: (+49) (0)651-97551-34
Fax: (+49) (0)651-97551-12
***********************************************************************

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