[Radiance-general] [HDRI] Photosphere (or equivalent) in Linux or Windows?

[Chamilothori Kynthia]

Hi Greg,

Thanks for proposing a solution so quickly - much better than my clumsy attempts at grep!

However, my calibrated image still has very low luminance values (< 1.0L) This makes sense: as I read from the File Format document in the Radiance references, the EXPOSURE variables in the header are cumulative, so I am essentially dividing all my values by 178 (which is my $ecorr). Am I doing the conversion (set ecorr=`ev "179*$img_val/$meas"`) incorrectly? :-)



Thanks for your help once again,

Kynthia




From: Greg Ward [mailto:gregoryjward at gmail.com]
Sent: mardi 7 juin 2016 17:45
To: Radiance general discussion <radiance-general at radiance-online.org>
Subject: Re: [Radiance-general] [HDRI] Photosphere (or equivalent) in Linux or Windows?

Hi Kynthia,

The corrected version of this command sequence is:

            (getinfo < capture.hdr  | sed 1a\
EXPOSURE=$ecorr ; getinfo - < capture.hdr) > calibrated.hdr

It's important to put the backslash immediately after the 'a' with no spaces for this to work.  This puts the EXPOSURE= line on the second line of the header, instead of after it.

The following will create a "slighly wrong" header that will still work -- this is what I usually do:

                echo EXPOSURE=$ecorr  > calibrated.hdr
                cat capture.hdr >> calibrated.hdr

Cheers,
-Greg


From: Chamilothori Kynthia <kynthia.chamilothori at epfl.ch<mailto:kynthia.chamilothori at epfl.ch>>

Date: June 7, 2016 6:30:37 AM PDT


Hi all,

Germán and Mehlika, thanks for introducing me to hdrscope, I'm installing it right now.
And thank you Nathaniel for solving the RAYPATH problem!

In case it helps someone else, I was using Greg's hdrgen and the combination of ra_xyze, pcompos and pvalue to calibrate an HDR image as described in this thread<http://www.radiance-online.org/pipermail/radiance-general/2011-April/007764.html> and I ran into the following error when applying the last line:

(getinfo < capture.hdr ; echo EXPOSURE=$ecorr ; getinfo - < capture.hdr) > calibrated.hdr

The output picture reads as  a 'bad picture format' with ximage and a closer look reveals that the EXPOSURE line that is added in the header is just above the -Y +X resolution parameters, with the empty line ("\n\n") before it, terminating the header before this new EXPOSURE variable.
Out of curiosity I put the empty line after the EXPOSURE (this time with no lines between the header variables), and now the HDR opens correctly with ximage with both EXPOSURE variables (original and new) but the luminance values are very low (<1L). I'm obviously doing something very wrong.
If I understand correctly, the error correction (and the added EXPOSURE variable) should ideally be very close to 179 based on the standard lumens/watt conversion - in my case it's 178.02 as the ratio of measured and generated luminance values is 0.99. Is this correct?

I've lent our copy of Rendering with Radiance to a student, so forgive me if I'm missing things that are explained there.
Let me know if I should make a separate message about this, as I am hijacking my own thread!

Thanks for all your help,
Kynthia
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