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(gimpprint.info)Weaving collisions

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Weaving collisions
------------------

   This perfect weave is not possible in all cases.  Let's look at
another example:

S=6,  J=4:

     0 *-----*-----*-----*
     1     *-----*-----*-----*
     2         *-----*-----*-----*
     3             *-----*-----*-----*
     4             ^   *-^---*-----*-----*
     5             |   ^ | *-^---*-----*-----*
                   OUCH!   ^ |   ^
                           |     |

Here we have a collision.  Some lines printed in later passes overprint
lines printed by earlier passes.  We can see why by considering which
row number is printed by a given jet number j (numbered from 0) of a
given pass, p:

     row(p, j) = p*J + j*S

   Because J=4 and S=6 have a common factor of 2, jet 2 of pass 0
prints the same row as jet 0 of pass 3:

     row(0, 2) = 0*4 + 2*6 = 12
     row(3, 0) = 3*4 + 0*6 = 12

   In fact, with this particular weave pattern, jets 0 and 1 of pass
p+3 always overprint jets 2 and 3 of pass p.  We'll represent
overprinting rows by a `^' in our diagrams, and correct rows by `*':

S=6  J=4:

     0 *-----*-----*-----*
     1     *-----*-----*-----*
     2         *-----*-----*-----*
     3             ^-----^-----*-----*
     4                 ^-----^-----*-----*
     5                     ^-----^-----*-----*