Visibility against an unknown background

[Ben Finney]

Grant Edwards <grante at visi.com> writes:

> The traditional way to draw lines on something with varying colors
> is to use the "xor" operator when drawing the lines.

But first, negotiate a patent license for this highly innovative and
non-obvious technique that is "owned" as US Patent #4,197,590.

    <URL:http://www.fourmilab.ch/autofile/www/chapter2_105.html>

Aren't monopolies on ideas wonderful?

-- 
 \     "I'd like to see a nude opera, because when they hit those high |
  `\   notes, I bet you can really see it in those genitals."  -- Jack |
_o__)                                                           Handey |
Ben Finney