[R] question about image command

[Mikyoung Jun]

Hello,

I have a question about image command. When you draw a image plot, and 
let's say we use gray scale. then how can I generate a little bar next to 
the plot which shows the grey levels and the values which corresponds to 
the grey level? ( it doesn't matter whether I am using grey level or not. 
It could be just any colors...)

The only way that I can do right now is overlaying contour plot on the 
image plot...

Thank you!