Created attachment 14135 [details]
ramp.pdf

Using .genordered from PostScript (or gen_ordered standalone), the turn on
order of cells in the supercell needs better dispersion, particularly in the
very light shades.

Seen with:

gs -dUseFastColor -r600 -sDEVICE=pbmraw -o x.pbm -c "<< /Frequency 133 \
  /Angle 45 /SuperCellSize 36 /Levels 255 >> .genordered  \
  /Default exch /Halftone defineresource { } settransfer 0.003 setsmoothness" \
  -f ramp.pdf

Other SuperCellSize values such as 72 also show room for improvement.

It is expected that increasing the SuperCellSize (-s) would improve the
visual quality of the threshold array.