What is a BW file?
Paul Haeberli is the developer of the BW file extension. It is an SGI (Silicon Graphics Image) format which is useful in saving monochrome images. It can also store RGB with or without alpha channels data, but it will use the .RGB or .RGBA extension in that case. It is a native format of SGI workstations and can be RLE (Run-Length Encoded) or uncompressed.
How to Open BW Files
How to Make BW Files
Exact steps for creating BW files will vary by program and operating system. Download one of the above listed programs and you should be able to follow typical procedure for opening files or creating files from the File menu. Typically you will select File > Open or File > New and continue through the prompts. Some programs may follow a different procedure for either creation or opening of files.