accessing a bitmaps pixels rgb values

Hi, I am a newbie to builder and need to extract rgb colour information from
a bitmap file for every pixel in the image.

I can open a bitmap and display it but cant find how to get at it on a pixel
level to extract the colour information.

If anyone knows how to access individual pixels of a bitmap to find the
colour information I would be grateful for any help.

Thanks in advance, Stew