[vtkusers] Convert grayscale image to rgb

[David Gobbi]

Hi Milan,

The vtkImageShiftScale operation is totally unnecessary here,
just set the range of the lookup table to the range of your data,
e.g.:

lookupTable->SetRange(0.0, VTK_UNSIGNED_SHORT_MAX);

I hope this helps.

  - David


On Thu, Jun 5, 2014 at 9:33 AM, Milan Vidakovic <milan.vidakovic at tp.rs> wrote:
> I managed to get decent results using the following formula. So, 16bit
> grayscale to RGBA:
>
> vtkSmartPointer<vtkLookupTable> lookupTable=
> vtkSmartPointer<vtkLookupTable>::New();
> lookupTable->SetNumberOfTableValues(VTK_UNSIGNED_CHAR_MAX + 1);
> lookupTable->SetRange(0.0, VTK_UNSIGNED_CHAR_MAX);
>
> // Iterate through every scalar value from 0-255
> // and fill RGB tables with scalar=R=G=B values
> for (int i = 0; i <= VTK_UNSIGNED_CHAR_MAX; i++)
> {
> double doubleIndex = static_cast<double>(i);
> lookupTable->SetTableValue(i,
> VTK_UNSIGNED_CHAR_MAX - doubleIndex,
> VTK_UNSIGNED_CHAR_MAX - doubleIndex,
> VTK_UNSIGNED_CHAR_MAX - doubleIndex,
> 1.0);
> }
>
> lookupTable->Build();
>
>                 vtkImageData* imageData <= 16bit grayscale
> imageData->AllocateScalars(VTK_UNSIGNED_SHORT, 1);
> // Cast 16bit grayscale image to 8bit and rescale
> vtkSmartPointer<vtkImageShiftScale> rescaler =
> vtkSmartPointer<vtkImageShiftScale>::New();
> rescaler->SetOutputScalarTypeToUnsignedChar();
> rescaler->SetScale(1.0 / (VTK_UNSIGNED_CHAR_MAX + 1));
> rescaler->SetShift(0);
> rescaler->SetInputData(imageData);
>
> // Map the input image using RGBA lookup-table
> vtkSmartPointer<vtkImageMapToColors> imageColorMapper=
> vtkSmartPointer<vtkImageMapToColors>::New();
> imageColorMapper->PassAlphaToOutputOn();
> imageColorMapper->SetLookupTable(lookupTable);
> imageColorMapper->SetInputConnection(rescaler->GetOutputPort());
>
>                 imageColorMapper->GetOutput() => 8bit RGBA
>
> There might have been a more elegant solution, but this is what worked for
> me.
>
> Thanks to all!
>
>
> On Wed, Jun 4, 2014 at 1:34 PM, David Cole <dlrdave at aol.com> wrote:
>>
>> > Hi David. Thank you very much for the example, it did push me a bit
>> > further. Another thing, I have a number of
>> > 16bit grayscale images that also need converting. In what way should
>> > I modify the lookup table to accommodate these files?
>>
>> See the updated example which I've put on the wiki now:
>>
>>     http://www.vtk.org/Wiki/VTK/Examples/Cxx/Images/ImageMapToColors
>>
>> You can use any of the classes that derive from vtkScalarsToColors as
>> the lookup table.
>>
>>     http://www.vtk.org/doc/nightly/html/classvtkScalarsToColors.html
>>
>> If you just use vtkLookupTable as in the example, you can just modify
>> the arguments to the SetRange call to cover whatever range of grayscale
>> values you want to map to color. Anything lower than the lower arg will
>> map to the lowest color, and anything higher than the higher arg will
>> map to the highest color... in between values get interpolated.
>>
>>     http://www.vtk.org/doc/nightly/html/classvtkLookupTable.html
>>
>> Please keep replies on the list so others may also benefit from the
>> discussion.
>>
>>
>> Thanks,
>> David C.