Re: Camera Profiling question
Re: Camera Profiling question
- Subject: Re: Camera Profiling question
- From: Eric Chan <email@hidden>
- Date: Sun, 14 Sep 2008 22:12:49 -0700 (PDT)
> In practice, if the sensor is reasonably linear, and
> the RAW values are linear light, then I'd imagine
> it's probably
> not going to make much difference whether the white balance
> is set pre or post profile (assuming the black point offset
> is taken care of in the RAW processing, and the profile is
> being
> used to transform into an RGB like working space).
Most current cameras that support raw formats are nearly perfectly linear up to just before the clipping point, in each channel (pretty easy to check with a series of test shots, if one examines the raw data).
Your point about the black offset is certainly relevant. This is why the DNG processing model performs the linearization step first, during which the black offset (if it exists) is subtracted out. Essentially the raw values are taken from their original [black level, white level] range and rescaled to [0,1], so from that point onward we're in normalized linear camera coordinates. White balancing and then the camera profile transform steps are applied immediately afterwards.
Regarding the order of operations, it would depend on whether the camera profile transform is linear or not. I'm sure you're aware of this (hence your comment about a RGB space) but this point may not be clear to all of the readers here. For instance, with the earlier Camera Raw profiles, they were strictly matrix-based and hence linear, so it wouldn't have mattered whether WB was performed before or after (actually the WB was simply folded into the color matrix). But if you have arbitrary non-linear adjustments (e.g., implemented via a lookup table) then all bets are off, even if the destination space is a RGB space.
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