NoteHeads vs duration

[Pierre Perol-Schneider]

Hi,

Please consider the following:

\version "2.19.46"

\score {
  \new Staff \relative c'' { c1 2 4 8 16 32 64 128 256 }
  \layout {
    \context {
      \Staff
      \omit Stem
      \omit Flag
      \override NoteHead.stencil =
        #(lambda (grob)
          (let ((duration (ly:grob-property grob 'duration-log)))
                (case duration
                  ((0) (grob-interpret-markup grob (markup "0")))
                  ((1) (grob-interpret-markup grob (markup "1")))
                  ((2) (grob-interpret-markup grob (markup "2")))
                  ((3) (grob-interpret-markup grob (markup "3")))
                  ((4) (grob-interpret-markup grob (markup "4")))
                  ((5) (grob-interpret-markup grob (markup "5")))
                  ((6) (grob-interpret-markup grob (markup "6")))
                  ((7) (grob-interpret-markup grob (markup "7")))
                  ((8) (grob-interpret-markup grob (markup "8")))
                  (else (ly:note-head::print grob)))))
        }
  }
}

How can I get access to the note head when duration is shorter that a fourth note ?

TIA.

Cheers,

Pierre