[vtkusers] [vtk-developers] Bug in vtkImageMapToColors

[Nicolas Rannou]

On May 9, 2011, at 1:50 PM, David Gobbi wrote:

> Hi Nicolas,
> 
> If you provide the new text that you would like to see in the documentation, I can modify the file and commit the change.
> 
>  - David
>  
> 
> On Mon, May 9, 2011 at 11:29 AM, Nicolas Rannou <Nicolas_Rannou at hms.harvard.edu> wrote:
> 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).

What about:

> 
> 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 first component (if the dataset attributes have multiple components). 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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