Yes, IIRC it's about an 18 byte binary header and then BGRABGRABGRA... or BGRBGRBGR... bytes for uncompressed (there's also an RLE mode, but I never use it). The only real gotchas are the channel ordering and that the image might be flipped top-to-bottom if you're not careful.

These days though, I use tend to use the even simpler PPM format. It uses normal RGB byte ordering from top to bottom, and it's simple enough that I can code a basic writer for it from memory:

    fprintf(stream, "P6 %d %d 255\n", width, height);
    fwrite(image, 1, height * width * 3, stream);

(Often, I won't even bother opening a file to write to. I'll just emit the image to stdout and then pipe it to Image Magick for display or to convert to a compressed image format for storage.)