HDRI list - Can someone help me better understand the pvalue o option?
http://radsite.lbl.gov/radiance/man_html/pvalue.1.html I have completed HDRgen for a large data set, and will apply exposure correction, vignetting correction, then use pvalue (with or without o) to apply the spot calibration using a grey card mask (according to below), and finally pvalue again (with or without o) to get useful results. This is in the context of the previous post for automating the spot calibration for a large number of HDRs using luminance meter and grey card in a scene. Do I let it at the default (+o)? Thank you, --- On Apr 14, 2011, at 12:52 PM, "Greg Ward" <[email protected]> wrote: > > >> Hi Kevin, >> >> What you ask is a very tricky scripting operation. If you know exactly >> where the point you want to calibrate is in every image, you can script it >> with some combination of the Radiance ra_xyze, pcompos, pvalue, and total >> programs. Let's say you know that you have a value of 322 cd/m^2 in the >> square from (x,y)=(300,450) to (380,530) -- y pixels measured from the bottom >> of the image and x from the left, you could compute the average using: >> >> set img_val=`ra_rxyze -o capture.hdr | pcompos -x 80 -y 80 - -300 -450 | >> pvalue -h -H -d -pG | total -m` >> >> You could then use this to compute a correction (calibration) factor to the >> image exposure: >> >> set meas=322 >> >> set ecorr=`ev "179*$img_val/$meas"` >> >> The 179 value is the standard lumens/watt conversion used in Radiance, and >> the 322 value is your measured luminance value. You then need to add the >> above to your image header, which can be accomplished with getinfo like so: >> >> (getinfo < capture.hdr ; echo EXPOSURE=$ecorr ; getinfo - < capture.hdr) > >> calibrated.hdr >> >> I hope this helps. >> >> -Greg Kevin Van Den Wymelenberg Integrated Design Lab Boise, Director College of Art & Architecture, Assistant Professor University of Idaho Boise Center www.uidaho.edu/idl ph. 208.724.9456 fx. 208.343.0001 306 S. 6th Street Boise, ID 83702
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