* @demohfe demonstrates the separation
* of an image into low frequency, 
* high frequ. edges and hf non-edges
* by P. W. Verbeek TU-DELFT
read trui
lmax A B 7  * maximum
lmin A C 7  * minimum
lmin B D 7  * lohull
add C B     * dynamic threshold, low freq
lmax C C 7  * uphull
add C D     * midian
cop B C
sub D C 127 * midian-dyth, hf edges
sub A D 127 * ori-midian, hf non-edges