[Radiance-general] conversion of digital pictures to Radiance?

[Greg Ward]

A minor correction to Rob's note -- you should actually fix the f-stop 
and vary only the shutter speed in your exposures, not the other way 
around.  The reason for this is that f-stops are not very reliable or 
repeatable on most cameras, but shutter speed is reasonably sure.  Here 
is an excerpt from the quickstart_pf.txt file that comes with 
Photosphere:

To create a high dynamic-range image, you need to start with
a set of "bracketed" exposures of a static scene.  It is best if
you take a series of 10 or so exposures of an interior scene looking
out a window and containing some large, smooth gradients both inside
and outside, to determine the camera's natural response function.
Be sure to fix the camera white balance so it doesn't change, and
use aperture-priority or manual exposure mode to ensure that only
the speed is changing from one exposure to the next.  For calibration,
you should place your camera on a tripod.  Take your exposure series
starting from the longest shutter time and working to the shortest in
one-stop increments.  Make sure the longest exposure is not all white
and the darkest exposure is not all black.  Once you have created your
image series, load it into Photosphere directly -- DO NOT PROCESS THE
IMAGES WITH PHOTOSHOP or any other program.  Select the thumbnails,
then go to the "File -> Make HDR..." menu.  Check the box that says
"Save New Response", and click "OK".  The HDR building process
should take a few minutes, and Photosphere will record the computed
response function for your camera into its preferences file, which
will save time and the risk of error in subsequent HDR images.
You will also have the option of setting an absolute calibration
for the camera if you have a measured luminance value in the scene.
This option is provided by the "Apply" button submenu when the
measured area is selected in the image.  (Click and drag to select.)
Once an HDR image has been computed, it is stored as a temporary
file in 96-bit floating-point TIFF format.  This file is quite
large, but the data will only be saved in this format if you
select maximum quality and save as TIFF.  Otherwise, the 32-bit
LogLuv TIFF format will be preferred (or the 24-bit LogLuv format
if you set quality to minimum).  You also have the option of saving
to the more common Radiance file format (a.k.a.  HDR format), or
ILM's 48-bit OpenEXR format.  If you choose not to save the
image in high dynamic-range, the tone-mapped display image can be
written out as a 24-bit TIFF or JPEG image.

-Greg