[R] How to plot image of contour in percent?

[yk]

I have searched this forum with keywords contour and percent, it only
give one irrelevent result.
My problems is how to plot contour in percent.
In my figure, I have use kde2d to generate density of an array with
two dimension point.
Using image and contour could plot it.
But the line contour generated represent absolute value of population,
not how much pecent point within this cycle.
So, i there any function which could accomplish it?To generate a cycle
which could tell me how much percent of points lies in this cycle.
Thank you for your attention