The individual bars were segmented automatically by
differentiation to find the transition
regions, and then robust statistics used to determine
an estimate of 
for each of the 11 steps, as well as the
black regions of the test pattern.
Using the known reflectivity of each of these 12 regions, a set of
12 ordered pairs 
was determined for each of the 19 exposures,
as shown in Fig 7(b).
Shifting these results appropriately (by the 
values,
to line them up, gives the ground-truth,
known response function, 
, shown in
Fig 7(c).