Input is a rendered Radiance picture.
By default, luminance is displayed on a linear scale from 0 to 1000 nits, where dark areas are blue and brighter areas move through the spectrum to red. A different scale can be given with the -s option. The default multiplier is 179, which converts from radiance or irradiance to luminance or illuminance, respectively. A different multiplier can be given with -m to get daylight factors or whatever. For a logarithmic rather than a linear mapping, the -log option can be used, where decades is the number of decades below the maximum scale desired.