Windows Form Print Black & White?

I been playing around with some code I found on internet and I am probably almost where I need to be. Using the printdocument I am able to get the active form in my project to print. That works fine. MY nextr issue was to get the form to print so that it is Black & white. No shading etc.. So I found a routine on internet that will take image and turn to B&W. Problem: IF a text box fields background color is too dark then the entire box shows up in black. If a text box field data is Selected it also is too dark and comes out white.her is code I found for turnign to B&W

Public Function PureBW(ByVal image As System.Drawing.Bitmap, Optional ByVal Mode As BWMode = BWMode.By_Lightness, Optional ByVal tolerance As Single = 0) As System.Drawing.Bitmap
Dim x As Integer

[code].....