After all the adjustments have been made, the Grayscale scan is ready to be converted to Bitmap mode. Converting to Bitmap mode will greatly reduce the file size, in fact it will be one eighth the size of the flattened Grayscale.

To convert the Grayscale scan to Bitmap mode, make sure the image is flattened then go to Image/Bitmap..., the Bitmap dialog box appears. The Input resolution should match the Output resolution and for Method select 50% Threshold. Click OK.

The file is now in Bitmap mode and contains only two colors, black and white. You can use the Pencil tool and white to clean up any dirt in the white areas.