Faststone image viewer can be used to create images that use only one bit per pixel. That is, the image will contain only pure white and pure black. Unlike grayscale images, a 1-bit image will not have any shades of gray. This can be useful if you want to scan and print old documents. Even if you use the black and white option in your scanner software, with old documents, you will most likely end up with a gray background. It would take a huge amount of ink to print such an image. 1-bit images solve this problem.
Steps
Step 1: Select the image you want to convert.
Step 2: From the Colors Menu choose Reduce Colors ➾ 2 colors (1bit). You can also use the keyboard shortcut Ctrl+Shift+1.
Step 3: Choose Save As to save as a new image.