Pick up data from a JNA Pointer

I'm currently working with jna . It's been a struggle to learn. but I ended up finding jnaerator that generates the entire interface with the methods directly with header.h . But I caught in a part. In a given method, the returns are as follows:

public interface RSAdvPreviewCallback extends Callback {
    void apply(int deviceHandle, int errorCode, Pointer imageData, int imageWidth, int imageHeight, int  quality, int status);
};

The Pointer imageData returns an image. But how to extract this information from object Pointer ?