exr to hdr conversion

[kimo.johnson]

Hi,

I've run into something strange trying to convert an exr to hdr using
pfstools (a different problem from the one I posted a few days ago).
The funny thing is that I ran into the same problem with Photoshop,
which is the reason I started looking for other tools to process HDR
images. In any case, I put a tarball up here:

http://www.cs.dartmouth.edu/~kimo/downloads/pfstest2.tar.gz

If I convert the exr to hdr as follows:

pfsinexr chrome1.exr | pfsoutrgbe chrome1.hdr

and open chrome1.hdr in Photoshop, I notice streaks that should have
been encoded as black were actually encoded as white (red channel). I
quickly searched this group and didn't find any messages about this,
and I apologize if this issue has already been covered.

Thanks,
Kimo

[Rafal Mantiuk]

Hi Kimo,

> If I convert the exr to hdr as follows:
>
> pfsinexr chrome1.exr | pfsoutrgbe chrome1.hdr
>
> and open chrome1.hdr in Photoshop, I notice streaks that should have
> been encoded as black were actually encoded as white (red channel).

The streaks you see are out-of-gamut colors, which cannot be encoded
in RGBE files. RGBE, unlike OpenEXR, does not encode negative values.
If you open your original files with pfsview and move the cursor over
the affected areas, you will notice that the value for R channel is
negative.

I would suggest using OpenEXR (more accurate, athough may crop large
values) or checking your HDR capture algorithm - if your camera's
primaries do not exceed those of sRGB, it may be a color calibration
problem.

Cheers,

Rafal

[Kimo Johnson]

Rafal,

Thanks again for the quick reply. I'm using Photoshop Merge to HDR
from 11 Nikon RAW images. I've been RGBE to transfer images between
HDRShop and MATLAB, but after your explanation I think I'll consider
another format.

Thanks,
Kimo

[Rafal Mantiuk]

Kimo,

> Thanks again for the quick reply. I'm using Photoshop Merge to HDR
> from 11 Nikon RAW images.

Photoshop merge is quite fast and convenient, but if you need more
accuracy, you can try pfscalibration. If DCRAW can read Nikon's raw
files, pfscalibration should be able to take them as an input.

Cheers,

Rafal

[Kimo Johnson]

Rafal,

Thanks for the tip. Yes, DCRAW can read the Nikon NEF format. I'll
give pfscalibration a try.

Thanks,
Kimo