将WriteableBitmap像素格式转换为c＃wpf中的Bgra32

I have a WriteableBitmap which loads the bitmap image from file(mostly bmp). The bitmap files I am using have different pixel formats such as Indexed8, Bgra32, etc etc. The problem is that my code only works for bgra32 pixel format. So I need help in converting the bitmaps to Bgra32 pixel format in c# wpf.I have a WriteableBitmap which loads the bitmap