Creating the mask of an image

I've made a function that creates the mask of an image using the API functions :

Declare Function GetPixel Lib "gdi32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long) As Long

and

Declare Function SetPixelV Lib "gdi32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long, ByVal crColor As Long) As Long

What I want to know is if the API already have one that makes that.

Someone had a program that would do this, I don't know who they are at the moment though.