How to get a raw capacity image on an Android device

I am stuck on how to get capacity image from android phone. Do you need to hack Android system to get capacitive image in android?

In the released Android API, this only allows me to get what point my finger touches the screen. But since the touchscreen uses capacitive sensors, I'm wondering how can I get the raw capacitive sensitivity data from the system? I guess I might need to hack the system for more information. Has anyone done this before? Or can you give me hints or directions where I should start?

Appreciate your help!