Greg confirmed my foggy memory about Photoshop and hdr headers. Just a
couple quick thoughts I wanted to share... If you have extra time and
energy, consider trying Greg's raw2hdr script
(http://www.radiance-online.org/pipermail/hdri/2012-February/000363.html).
However, there's really no problem with using jpegs and
hdrgen/photosphere. I have personally found that with creating and using
a good calibration method and file (see this:
http://www.jaloxa.eu/webhdr/calibrate.shtml), and being consistent with
the whitebalance setting, the jpeg method produces extremely accurate
luminance images (r^2 > .996). As Greg just mentioned, a photometer to
dial in the range would further improve the 1:1 hdr to real photometric
values. Finally, I will cautiously note that in one experiment, I found
that jpegs were more accurate than nefs (perhaps due to random
fluctuations in estimating the calibration response curve), but I
haven't repeated that experiment. For both image types (jpg and nef),
the covariances between image sample and photometer were still extreme
(r^2 ~ .99).
Happy imaging!
Chris
On 4/24/13 12:09 PM, Gregory J. Ward wrote:
Yes, Photoshop strips the header from Radiance (HDR) images, including
the view parameters. You can always add them back in afterwards using
the Radiance "vinfo" command (on Unix anyway). You'll still have the
problem that Photoshop doesn't do any kind of absolute calibration on
HDR images, so if evalglare needs absolute quantities, it won't have
them. Adding the correct exposure requires having an in-scene
luminance measurement for calibration.
This is why it's generally better to use hdrgen or Photosphere for HDR
creation in photometric applications, although a calibration
measurement will improve your accuracy even more.
Cheers,
-Greg
*From: *Avinash Gautam <[email protected]
<mailto:[email protected]>>
*Date: *April 24, 2013 9:37:03 AM PDT
*
*
Hi Chris,
I think Adobe Photoshop must have messed up with the header files
while creating the HDR. I was about to try the methods you sent in
your earlier email but seems there is a shorter route by using hdrgen
or photosphere to create the HDR file. I am a novice in this area and
your help is really appreciated.
Thanks again for all your help.
Regards,
Avinash
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