Change the raw file during the acquisition of an image

[Damiano]

Hi to all,
I am evolved in a project:I'm trying to change the raw buffer during the acquisition of an image using a self-made module.For the first step of my project I'm trying to overwrite the raw_info.buffer with this code to have a white image saved in the sd but nothing happen:

memset(raw_info.buffer, 0, raw_info.frame_size);

I can post the full code if needed.
Thanks for any help,
Damiano