DrawString function

Dear code gurus,

I am using a "DrawString" function to display text in bitmap. For whatever reason, the text displayed have some "shading" as on the picture below. In this picture I have used Arial 20pt regular font and "Black" brush. You may not see the problem due to the size of the picture, but if you "blow it up" you will see that different shades are used to draw the text.

What am I doing wrong? What should I fix to display the text only in black on my bitmap, no additional colors.