Setting Web Cam formate form jmpg to yuy2

[A125740364]

Dear all
I can start the webcam with aforge.net.
But i foud the picture has some noisy.
So i open another software also build with Direct Show -->AmCap.
Finally i found the noisy is from the compression.

In Amcap ,I can set the formate betwin mjpb or yuy2.
Does anybody know how could i seeting the formate from mjpb to yuy2?

BILL