| I don't thinkg that's how Darktable works... Darktable doesn't clip
| highlights in its pipeline...
My experience is that darktable will definitely blow highlights in
the final rendered image when they are not blown in the original
RAW. Depending on the image this may be blown in only some RGB channels
or in all of them. I think (but have not verified) that this process
does not distort colours (apart from sometimes taking colours to white)
but it does lose detail.
(Since darktable uses high-precision floating point internally, I assume
that these values are never clipped during processing and thus remain
theoretically recoverable with the right manipulation.)
If you want to see this, I'll point to my sample NEF:
http://www.cs.toronto.edu/~cks/tmp/darktable/DSC_1101.NEF
Look at the difference in output RGB values and detail in the lead
policeman's yellow jacket in a version with and without the base curve.
With the base curve applied, the darktable color picker says that spots
go to, eg, 255/255/122 when in the pre-base-curve version the same spot
is at 223/187/75. This wipes out a chunk of detail and makes the result
look glaringly bright.
(I believe that part of the overall confusion about this is that many
RAW processors use 'highlight recovery' to refer to two different
processes: dealing with clipped channels in the RAW and 'recovering'
things that were unclipped in the RAW but which have become blown out
in processing. I believe that Darktable's 'highlight recovery' module
is specific to clipped RAW channels, which we can see from its very
early place in the processing pipeline; it takes effect even before
demosaicing[*].)
- cks
[*: ... although after white balance is applied, which is its own issue,
since in theory white balance multipliers can push a channel over what
would normally be blown. If you want to see a close approximation
of the RAW channel data you need to manually set the white balance
multipliers to 1.0 (aka 'UniWB'). If you want to do this kind of
examination you may be better off with a program that looks at
the RAW file from a more numerical perspective. One such one that I
know about is Rawdigger, http://www.rawdigger.com/; it's a Windows/Mac
program but I've successfully run it under Wine in the past. I don't
know if there's a handy Linux equivalent.
]
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