[vtkusers] alpha value in vtkImageActor

[francesco caruso]

Hello

I'd like to set the alpha-value pixel by pixel in a vtkImageActor

I can render a vtkImageActor in which UnsignedCharArray is of type 
(RGBRGBRGB....)
but I can't render a vtkImageActor in which UnsignedCharArray is of type
(RGBARGBARGBA....)

why?

Here are the sources...

Thanks in advance to anyone try to help me!

def RawFileToUnsignedChar(filename,xsize,ysize,bpp):#function to get an 
unsigned char array
  	print"raw file parsing..."
  	f=open(filename,"r")
  	f.seek(0)
  	image = vtk.vtkUnsignedCharArray()
  	image.SetNumberOfComponents(bpp+1)
  	for i in range(xsize*ysize):
  		image.InsertNextTuple4(ord(f.read(1)),ord(f.read(1)),ord(f.read(1)),1)
  	print "done."
  	print image.GetTuple4(1)#check if it works
  	return image
	
def UnsignedCharArrayToImageActor( array,xsize,ysize,bpp ):
	imageImporter = vtk.vtkImageImport()
  	imageImporter.SetDataScalarTypeToUnsignedChar()
  	imageImporter.SetNumberOfScalarComponents(bpp+1)
  	imageImporter.SetDataSpacing(1,1,1)
  	imageImporter.SetWholeExtent(0,xsize-1,0,ysize-1,0,0)
  	imageImporter.SetImportVoidPointer( array.GetVoidPointer(0) )
  	imageImporter.SetDataOrigin(-(xsize-1)/2,-(ysize-1)/2,0)
  	imageActor = vtk.vtkImageActor()
  	imageActor.SetInput( imageImporter.GetOutput() )
  	return imageActor