Dear list and Hi Greg,
In the recent raw2hdr bundle you packaged for Yulia
http://www.radiance-online.org/pipermail/hdri/2012-February/000363.html
there's a man page for hdrgen that list some options which do not appear
in the man page that comes with the LINUX download you have on
http://anyhere.com/
I have just discovered that the -x option does actually exist in the
LINUX version of hdrgen, which is from around 2006, I think.
In the more recent (MacOS) version, the -x option is described as
"-x Toggle over- and under-exposed image removal. Normally
“off,” this option causes unnecessary exposures that are too light or
too dark to contribute useful information to be automatically ignored."
I have always lived under the impression that 'useful information' is
limited by pixel values of 200 in the darkest JPEG, and 20 (out of 255)
in the brightest. I really don't remember where I took this from, but it
must have been a post on the hdri list which I am unable to find now. Sorry.
In your message to hdri just recently,
http://www.radiance-online.org/pipermail/hdri/2012-February/000365.html
you stated
"Specifically, all values in the short exposure's histogram should be be
below 245."
which is different to the 200 threshold I mentioned above.
I have been experimenting with HDR photography for glare studies (think
UGR), and have noticed some discrepancies in the results that one gets
if hdrgen is run with and without the -x option. I was therefore
wondering what hdrgen considers as
"too light or too dark to contribute useful information". I would think
that this is decision is made based on the value of the
darkest/brightest pixel in the image. Is this assumption correct, and if
so, what are the threshold values that are used with the -x option?
Kind regards
Axel
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