Hugin is using absolute ev values in the exr files. Therefore clipping can
occur, when the value range of the exr file is overrun (as already found out).
A possible solution is the use relative ev values in the exr files (Implemented
in changeset 7b8ada736647). This changes the behaviour when outputting exr
files. Now the output exposure value has an influence on the exr files and
needs to be set to a middle exposure also for exr output (when setting the
output exposure value to zero, the old behaviour is retained). I hope that this
fixes the overflow and the final output has no more black areas.
Please test, if this does not break other side of the exr output and report
back. Thanks.
** Changed in: hugin
Status: Confirmed => Fix Committed
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https://bugs.launchpad.net/bugs/678694
Title:
EXR files quietly clipped (black rectangles in output)
Status in Hugin - Panorama Tools GUI:
Fix Committed
Bug description:
The EXR file format has a maximum encoding value of 65504. The Hugin
data flow maintains the absolute exposure through use of the Ev field
which effectively scales pixel values. When using Hugin/Nona on an
HDR series that includes very bright elements (such as a very bright
sky with a very short exposure), some pixels end up with values above
65504. When these are written out by Nona, those pixels are written
as NaN's in the EXR output file.
If enblend is then used, the problem is further exacerbated. A
single NaN pixel results in NaN for entire rectangle of enblend's
pyramids. The end result are large black rectangles in the output
file.
If output is changed to TIFF, then everything works fine.
Nona should warn when clipping occurs and then output the maximum
possible value rather than a NaN. I assume this is the OpenEXR
library itself and probably affects other applications. In fact, if
a TIFF generated as above is opened in PhotoShop, it looks fine, but
if it is resaved as EXR, the same NaN pixels are created.
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