Change pixelvalues

Question

Hello, I've made a .NET program to manipulate pixels on a bitmap. The user can move his/her mouse on the bitmap and the program manipulates those pixels that the user passed with his/her mouse. I do this using the getpixel/setpixel functions. But I was wondering if there is a way of speeding up this proces, by changing a whole range of pixels that lie near the path the user follows with his mouse. Can I do this with a pen or brush? So I want something like the pencil(paintbrush) in Windows Paint. But how can I do this efficiently in C#?