fv is an HDRI viewer. It utilizes OpenGL and GLUT so that it is highly
portable. 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, bzip2, or xz. 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.

The command line options are:

  fv.exe [OPTION]... [FILE]...
  -g, --gamma=GAMMA
          use GAMMA as the gamma value (default 2.200000).
  -t, --title=TITLE
          use TITLE as the string displayed in the titlebar (default fv).
  -h, --help
          display this help and exit.
  -v, --version
          output version information and exit.

The drag-and-drop onto the executable file (or its shortcut) is also
supported on Windows.

The displayed image can be moved by dragging or arrow keys. Other
functions can be invoked from the right-click menu or by the following
keys:

  E/I     Zoom In
  W/O	  Zoom Out
  Q/P	  Reset Zoom
  F/J	  Expose With the Current Pixel
  B	  Expose Automatically
	    * This is done based on the log-average luminance found in
	      Eric Reinhard's "Photographic Tone Reproduction for
	      Digital Images"
	      (http://www.cs.utah.edu/~reinhard/cdrom/, see also
	      erratum), but only for non-zero pixels. This approach is
	      better than just adding a small delta and works nicely
	      for many images.
  D/K	  Expose Up
  S/L	  Expose Down
  A/;	  Reset Exposure Scale
  C/M	  Flip Horizontally
  V/N	  Flip Vertically
  Space	  Reset Origin
  Enter	  Save as PNG
	    * This saves the image in the current directory with a
	      name determined from the current time.
  Z       Toggle Full Screen
  Esc     Quit

# Notes for MacOSX:
# * The right button is emulated by "ctrl-click" for a single-button
#   mouse. If the mouse has multiple buttons, the GLUT for MacOSX
#   doesn't emulate the right button. You need to enable "the sub
#   button" on the mouse control panel. The default setting assigns
#   extra buttons to Expose, etc., so please be careful.
# * Running multiple fv instances causes the following log messages:
#   CFMessagePort: bootstrap_register(): failed ...
#   CFMessagePortCreateLocal(): failed to name Mach port ...
#   These are harmless so please ignore.
