If you search in the German helpfile for "weiße" you get the results attached in the image. The second "Weißen Hintergrund entfernen" should be "Weiße Bildanteile entfernen".
I am not happy with the translation anyway. First try was using "Weißen Hintergrund entfernen" applying on an image with a black signature on a white background (background = Hintergrund). Naturally nothing happened, so I tried next "Weiße Bildanteile entfernen". Maybe the translation could be made more clear, but I have no clue for a better translation.