For a Trimap, how do to calculate the number of pixels in background, foreground and unknown region?

Hi all,

I have attached a trimap image on which i am working. I need to determine the number of pixels which are definitely background, definitely foreground and in the unknown region. Can anyone help?

Thanks

[Image Analyst]

I never heard of a trimap. You forgot to attach your image. Please define what parts of your image (once we can actually see it) are foreground, background, and unknown.