.\" RCSid "$Id: phisto.1,v 1.4 2008/11/10 19:08:17 greg Exp $"
.TH PHISTO 1 3/12/98 RADIANCE
.SH NAME
phisto - compute a luminance histogram from one or more RADIANCE pictures
.SH SYNOPSIS
.B phisto
.B "picture .."
.SH DESCRIPTION
.I Phisto
is a script that calls
.I pfilt(1),
.I rcalc(1)
and
.I 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.
.PP
The primary function of this script is to precompute histograms for the
.I pcond(1)
program, which may then be used to compute multiple, identical exposures.
This is especially useful for animations and image comparisons.
.SH EXAMPLE
.PP
To compute two identical tone mappings for image1.hdr and image2.hdr:
.IP "" .2i
phisto image1.hdr image2.hdr > both.histo
.br
pcond \-I \-h image1.hdr < both.histo > image1m.hdr
.br
pcond \-I \-h image2.hdr < both.histo > image2m.hdr
.SH AUTHOR
Greg Ward Larson
.SH "SEE ALSO"
histo(1), pcond(1), pfilt(1), pvalue(1), rcalc(1), total(1)