Once you have assembled a good reflectogram, you will want to print it, or to use it in other computer programs. The best way to do this is to save the final image in TIFF or JPEG format, and then load it into the new application -- see §4.3.
There are a couple of points to bear in mind: first, like any image, reflectograms look best on paper if you sharpen them up a little first. Click on Filter=>Custom_convolution, open up the row, right click on the matrix button, select Replace from file, navigate to the VIPS data directory (probably the last item in the directory pulldown), and load rachel.con.
Secondly, you will need to try several prints with different contrasts and brightnesses to get a good match between the paper and the screen, try Image=>Adjust_scale_offset. You may even want to fiddle with the gamma, try Image=>Adjust_gamma.
Finally, you may not need a full resolution image. For almost all printers there's no point going over about 300 dpi (dots per inch), or about 3000 by 2000 pixels for an A4 page. To reduce the size of an image, use Resize=>Resize_image.