[HDR-photo] Color shift when converting to HDR with Photomatix

[Royce Howland]

Jim Bell wrote:
> [...]  It looks like maybe Photomatix is not interpreting the
> white balance in the metadata correctly. If I convert a nicely exposed 
> RAW file into an HDR and then look at the original file vs the new HDR 
> image, the result is always way too much yellow in the HDR. Any thoughts?

In my experience, the interpretation of white balance information varies 
across different RAW converter engines. Photomatix uses an engine called 
dcraw, and I'd expect any other dcraw-based application to convert the 
same file with the same look in terms of WB. Likewise I would expect 
Lightroom and Adobe Camera Raw to look the same since they both use the 
same engine -- ACR. However different RAW converters like Capture One, 
ACR/LR, Aperture, the camera vendor's software, etc. may look different 
than Photomatix (and each other).

You can adjust the WB in Photomatix when blending multiple RAW files 
together. However when doing "pseudo-HDR" processing of a single RAW 
file there is no option to adjust the WB and what is used is the "as 
shot" WB. In that case, if you prefer it to look different your best bet 
is to convert the RAW in your favorite converter and feed a 16-bit TIFF 
to Photomatix. We had a discussion here a few weeks ago about the 
relative benefits of doing separate RAW conversion vs. using Photomatix 
to process RAW's; if you search the list's archives you'll find it.

Note that there also may be some color management issues at work here. 
The actual RGB numbers in an image may be interpreted according to 
different color spaces by each different application, which may make 
them look different when displayed to the screen. Photomatix Pro 2.4 has 
begun to introduce some color management functionality, but it isn't 
complete. In particular, when processing a single RAW file you can't 
specify how to interpret the final RGB color primaries. Whereas when 
merging multiple RAW files you get to choose between sRGB, Adobe RGB and 
ProPhoto RGB.

In general, color management of HDR images is a dicey proposition 
because most HDR image formats and software don't really support CM of 
32-bit images. Depending on which files, color spaces, applications and 
CM settings you're dealing with, even an identical file's colors may 
look different. So you can't necessarily compare apples to apples 
between Photomatix's display and other applications' displays.

Unless you always use sRGB for everything, you need to take final 
versions of the images, assign the appropriate color spaces, and look at 
them side by side in the same (ideally color managed) viewer application 
to really tell the differences in color.

Royce Howland
Calgary, Alberta