[vtkusers] How to use vtkImageGradient?

[wang minyou]

Hello everyone,

I have some problem to use vtkImageGradient. According to the example in 
vtk-doc, I use vtkImageGradient to do image processing. But in runtime 
occurs some errors in vtkOutputWindow, which says:vtkImageGradient 
(019200A0): Execute: input has more than one components. The input to 
gradient should be a single component image. Think about it. If you insist 
on using a color image then run it though RGBToHSV then ExtractComponents 
to get the V components. That's probably what you want anyhow.

But I want to do the Gradient of the grey level of the image.How can I do 
that?
Thank you very much!

some codes are as follow:
vtkImageGaussianSmooth* pGaussianSmooth=vtkImageGaussianSmooth::New();
pGaussianSmooth->SetInput(bmpReader->GetOutput());
pGaussianSmooth->SetStandardDeviation(1.0);
pGaussianSmooth->SetDimensionality(2);
pGaussianSmooth->SetRadiusFactors(10,10,0);

vtkImageGradient* imgGradient=vtkImageGradient::New();
   imgGradient->SetInput(pGaussianSmooth->GetOutput());
   imgGradient->SetDimensionality(2);

vtkImageMagnitude* imgMagnitude=vtkImageMagnitude::New();
   imgMagnitude->SetInput(imgGradient->GetOutput());

// non maximum suppression
vtkImageNonMaximumSuppression* nonMax=vtkImageNonMaximumSuppression::New();
    nonMax->SetVectorInput(imgGradient->GetOutput());
    nonMax->SetMagnitudeInput(imgMagnitude->GetOutput());
    nonMax->SetDimensionality(2);

vtkImageConstantPad* pad=vtkImageConstantPad::New();
    pad->SetInput(imgGradient->GetOutput());
    pad->SetOutputNumberOfScalarComponents(3);
    pad->SetConstant(0);

vtkImageToStructuredPoints* i2sp1=vtkImageToStructuredPoints::New();
    i2sp1->SetInput(nonMax->GetOutput());
    i2sp1->SetVectorInput(pad->GetOutput());

// link edgles
vtkLinkEdgels* imgLink=vtkLinkEdgels::New();
    imgLink->SetInput((vtkImageData*)i2sp1->GetOutput());
    imgLink->SetGradientThreshold(2);

//threshold links
vtkThreshold* thresholdEdgels=vtkThreshold::New();
    thresholdEdgels->SetInput((vtkDataSet*)imgLink->GetOutput());
    thresholdEdgels->ThresholdByUpper(10);
    thresholdEdgels->AllScalarsOff();

vtkGeometryFilter* gf=vtkGeometryFilter::New();
    gf->SetInput((vtkDataSet*)thresholdEdgels->GetOutput());

vtkImageToStructuredPoints* i2sp=vtkImageToStructuredPoints::New();
    i2sp->SetInput(imgMagnitude->GetOutput());
    i2sp->SetVectorInput(pad->GetOutput());

//subpixel them
vtkSubPixelPositionEdgels* spe=vtkSubPixelPositionEdgels::New();
    spe->SetInput(gf->GetOutput());
    spe->SetGradMaps(i2sp->GetOutput());

vtkStripper* strip=vtkStripper::New();
    strip->SetInput(spe->GetOutput());

vtkPolyDataMapper* dsm=vtkPolyDataMapper::New();
    dsm->SetInput(strip->GetOutput());
    dsm->ScalarVisibilityOff();

pRenWin->AddRenderer(pRender2);
pRender2->SetViewport( 0.5 , 0.0 , 1.0 , 1.0 );
pRender2->SetBackground( 1.0 , 1.0 , 1.0 );	
    
vtkActor * myActor = vtkActor::New();
myActor->SetMapper(dsm);
pRender2->AddActor(myActor);

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