a question about gdk-pixbuf

["li sha" <no1tom gmail com>]

hi, every one,

I had a question about gdk-pixbuf. I want to show some bmp files and finished the job by following steps:
1. create a pixbuf using gdk_pixbuf_new_from_file() 
2. draw that pixbuf using gdk_draw_pixbuf()
it works fine, but I noticed that those bmp files all have a background color (pink), and I want to hide it.

I think it has something to do with mask, but I don't which function should I use, could it be gdk_pixbuf_render_threshold_alpha(), or gdk_pixbuf_render_pixmap_and_mask()? and how to use it? 

Is there any one who can help me? many thanks!

Sha li