phisto(1) compute a luminance histogram from one or more RADIANCE pictures


phisto picture ..


Phisto is a script that calls pfilt(1), rcalc(1) and histo(1) to compute a histogram of log luminance values for foveal samples in the given picture files. A foveal sample covers approximately 1 degree, though this script does not use this exact area. The minimum and maximum values are determined, and 100 histogram bins are uniformly divided between these extrema. Foveal samples less than 1e-7 candelas/sq.meter are silently ignored. If no picture is named on the command line, the standard input is read.

The primary function of this script is to precompute histograms for the pcond(1) program, which may then be used to compute multiple, identical exposures. This is especially useful for animations and image comparisons.


To compute two identical tone mappings for image1.hdr and image2.hdr:

phisto image1.hdr image2.hdr > both.histo
pcond -I -h image1.hdr < both.histo > image1m.hdr
pcond -I -h image2.hdr < both.histo > image2m.hdr


Greg Ward Larson