Continuous buffer for direct access - How To ???

I'm working with a Frame Grabber that need a buffer (like a C/C++ buffer:
byte* pBytes = new bytes[100]), this buffer must be continuous for the frame
grabber to access any part of it directly and not through wrapping methods
,but I do not know how, and if, I can do that in C#.
I also need to work with this buffer, which contain image, for image
processing.

How can get direct access to the buffer that should be continuous for the
Frame Grabber???

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Regards
Sharon G.