fv is an HDRI viewer. Currently supported formats are the followings:
* Greg Ward's HDR (also known as Radiance/PIC/RGBE). See
  http://www.graphics.cornell.edu/~bjw/rgbe.html for details.
* Paul Debevec's PFM (Portable Float Map). See
  http://netpbm.sourceforge.net/doc/pfm.html for details.

fv reads data from the standard input or files specified as
arguments. In the latter case, each file may be compressed one with
gzip or bzip2. The file may also change after fv is invoked, except
its header part. fv checks whether the file changes and updates the
display if necessary. This feature is useful for checking intermediate
outputs from renderers.

WWW: http://www.eaflux.com/fv/