GIMP :: Generate Mask File For Scientific Image Processing?

I opened a 1024x1024 image in GIMP, and manually broke it up into fully black and fully white sections. I'd like to output a file which is just a simple binary array of 8 bit numbers, such that every black pixel in the image has the value 0, and every white pixel has the value 1. This way, I can open it in my C program and then load the array into memory using the fread function.

I haven't been able to work out how to do this. I need to avoid using any files with metadata in them...And unfortunately, even the ppm format has a handful of characters at the beginning. Is there a way to do this?