The characteristic values are, for example, four values, namely a maximum value, a minimum value, an average value, and a median value, of scale converted data in each band. The four values of the first band are denoted by Amax (maximum value), Amin (minimum value), Aave (average value), and Amed (median value). The four values of the second band are denoted by Bmax, Bmin, Bave, and Bmed. Likewise, the four value of the third band are denoted by Cmax, Cmin, Cave, and Cmed, and the four values of the fourth band are denoted by Dmax, Dmin, Dave, and Dmed.

The normalization factor computation unit 216 computes a standard value, based on four characteristic values, for each band.

When the standard value of the first band is denoted by Astd, the standard value Astd is expressed by the formula (1) below.
Astd=Amax×0.15+Amin×0.15+Aave×0.3+Amed×0.4??(1)

When the standard value of the second band is denoted by Bstd, the standard value Bstd is expressed by the formula (2) below.
Bstd=Bmax×0.25+Bmin×0.25+Bave×0.4+Bmed×0.1??(2)

When the standard value of the third band is denoted by Cstd, the standard value Cstd is expressed by the formula (3) below.
Cstd=Cmax×0.4+Cmin×0.1+Cave×0.3+Cmed×0.2??(3)

When the standard value of the fourth band is denoted by Dstd, the standard value Dstd is expressed by the formula (4) below.
Dstd=Dmax×0.1+Dmin×0.1+Dave×0.5+Dmed×0.3??(4)

When the normalization factor is denoted by Std, the normalization factor Std is expressed by the formula (5) below.
Std=Astd×0.25+Bstd×0.4+Cstd×0.25+Dstd×0.1??(5)