Conversions between representations
       unsigned   bytes   shorts   float
min value     0    -128   -2048     -1
maxval     255   127   2047      1
medianval m     127.5   -0.5    -0.5      0
range r     255    255    4095      2
As shown in table a pixel prin representation r is converted
to a pixel ps in representation s by the operation:
ps = ms+(rs(pr-mr))¸rr