Accordingly with KDE bugzilla entries #177827 and #218906, i have slightly modified the vignetting tool, now you can add vignetting to your pictures:
Vignetting can be used as a creative tool to focus attention to the center of the picture.
This feature will be included in digiKam 1.1.0. I hope you will like it. Please provide feedback !
This is a companion discussion topic for the original entry at https://www.digikam.org/news/2010-01-25_new_tool_to_add_vignetting/