[vtkusers] RGB to RGBA

[francesco caruso]

Hello
I've got to "translate" an rgb unsigned char array into an RGBA image data.
I can translate it into an RGB image data in the way as follow:
void v4aDispImage(unsigned char* image)
{
	vtkImageImport* imageImporter = vtkImageImport::New();
  	imageImporter->SetDataScalarTypeToUnsignedChar();
  	imageImporter->SetNumberOfScalarComponents( bpp );
  	imageImporter->SetDataSpacing( 1,1,1 );
  	imageImporter->SetWholeExtent(0,xsize-1,0,ysize-1,0,0);
  	imageImporter->SetDataOrigin(-xsize/2,-ysize/2,0);
  	imageImporter->SetImportVoidPointer( image );
  	imageActor->SetInput( imageImporter->GetOutput() );
	[..]
}

How can I get an RGBA imagedata with A = 0 instead?

thanks in advance