[vtkusers] [vtk-developers] Bug in vtkImageMapToColors

[Nicolas Rannou]

Thanks David, 

yes such a feature to get the scalar range over all the components would be nice.
Maybe we should also update the documentation (http://www.vtk.org/doc/nightly/html/classvtkDataSet.html#a9c8f06877f41b3e1944f2d10281083a6).

virtual void vtkDataSet::GetScalarRange	(	double 	range[2]	)	[virtual]
Convenience method to get the range of the scalar data (if there is any scalar data). Returns the (min/max) range of combined point and cell data. If there are no point or cell scalars the method will return (0,1). Note: Update needs to be called to create the scalars. THIS METHOD IS THREAD SAFE IF FIRST CALLED FROM A SINGLE THREAD AND THE DATASET IS NOT MODIFIED



To  highlight that it computes the scalar range on the first component?

Thanks!

Nicolas

On May 7, 2011, at 5:25 PM, David Gobbi wrote:

> The only way that I know of is to get the range directly from the scalars,
> 
> double range[2];
> data->GetPointData()->GetScalars()->GetRange(range, component);
> 
> Personally, I would not be opposed to changing vtkDataSet::ComputeRange()
> so that it computed the range over all components.
> 
>  David
> 
> 
> On Sat, May 7, 2011 at 1:37 PM, Nicolas Rannou
> <Nicolas_Rannou at hms.harvard.edu> wrote:
>> Hi David,
>> 
>> Thanks for the clarification.
>> Which is the best practice to get the scalar range of each component then?
>> 
>> 
>> On May 6, 2011, at 5:53 PM, David Gobbi wrote:
>> 
>>> Hi Nicolas,
>>> 
>>> The GetScalarRange() method computes the scalar range of the first component.
>>> 
>>> - David
>>> 
>>> 
>>> On Fri, May 6, 2011 at 3:00 PM, Nicolas Rannou
>>> <nicolas_rannou at hms.harvard.edu> wrote:
>>>> Hello,
>>>> 
>>>> I'm experiencing a strange behavior in VTK which might be a bug.
>>>> It took me a while to locate the issue:
>>>> 
>>>> if I create a LUT with a NULL red component:
>>>>   iRed = 0;
>>>>   iGreen = 255;
>>>>   iBlue = 255;
>>>>   iAlpha = 255;
>>>>   double iRange[2] = {0, 255};
>>>> 
>>>>   vtkSmartPointer<vtkLookupTable> lut =
>>>>       vtkSmartPointer<vtkLookupTable>::New();
>>>>   double* HSV = vtkMath::RGBToHSV(iRed,iGreen,iBlue);
>>>>   lut->SetAlpha(iAlpha);
>>>>   lut->SetHueRange(HSV[0], HSV[0]);
>>>>   lut->SetSaturationRange(1, 1);
>>>>   lut->SetValueRange(0, 1);
>>>>   lut->SetRange(iRange);
>>>>   lut->Build();
>>>> 
>>>> I color my image with this LUT:
>>>> 
>>>>   vtkSmartPointer<vtkImageMapToColors> coloredImage =
>>>>       vtkSmartPointer<vtkImageMapToColors>::New();
>>>>   coloredImage->SetLookupTable(iLUT);
>>>>   coloredImage->SetInput( iImage );
>>>>   coloredImage->PassAlphaToOutputOff();
>>>>   coloredImage->SetOutputFormatToRGB();
>>>>   coloredImage->Update();
>>>> 
>>>> then:
>>>>   double* range = coloredImage->GetOutput()->GetScalarRange();
>>>> returns [0,0].
>>>> then everything I do with this image is messed up...
>>>> 
>>>> If iRed != 0, the scalar range of the "coloredImage" will be correct then my
>>>> pipeline is working.
>>>> 
>>>> Am I doing something wrong?
>>>> 
>>>> Thanks,
>>>> 
>>>> Nicolas

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