how to change color depht

[dcelso]

Hello to all. I have a 8bits bmp and i like convert it in 33 bits to increase colors to use in his pixels.
In Delphi i load the file with tbitmap and after i change the pixelformat property to pf32bit and it automatically convert in 32 bits. Doing the same in Lazarus daily 1.1 windows i obtain a black image.
So hocan i do it?
Thanks