described previously, on the upper left corner of the Joos
Vijd panel. Figure 4(a) shows that part of the painting and its corresponding
crack map. A rather simple analysis consists of counting
the number of crack pixels in a sliding window of 100 # 100.
In doing so we obtain a crack density map (see Figure 4) where we
can identify low crack density zones as well as high crack density
zones. The lowest (and highest) crack density zones are obtained
automatically by hysteresis thresholding, where the first chosen
threshold is chosen to be very close to the minimum (respectively maximum)
value of the crack density. Painting conservators confirmed
that the areas of lowest density marked in white in Figure 4(d) are
old losses covered with retouching that also overlap on the surrounding
original paint. Other zones of low crack density however