acessing to iphone camera data only with API

I would like to access in real time to the data of the camera to get the hue of several points in order to guide the user (inform him when is the best moment to take the picture). The application wi开发者_StackOverflowll be probably available on the appstore and then I want to just use allowed API. I've seen a lot of similar topics, some of them telling this is possible but none of them showing a solution.

Do you have any idea for this?

Thanks in advance :)

You need the undocumented UIGetScreenImage() function; an Apple representative recently stated their approval of the use thereof in the iPhone developer forums.