| > 1. (1) In practice, there are some non-linearities in the darkest
| > shadows and brightest highlights. Also, some cameras, e.g the
| > Nikon D2X, preprocess the sensor data before the ADC.
| >
| > I admit I deliberately suckered you to see whether you'd actually read
| >
|
| what doe "preprocess the sensor data before the ADC" mean ?
|
| I can't imagine what sort of preprocessing you can/would do on the
| analogic data...
|
| (that's a generic question, but i'm a bit curious)
I don't have an answer (and I have no idea what dpreview means here),
but some cameras are known to manipulate the RAW data. Specifically,
I know that Nikon does hot pixel suppression *in the RAWs* under some
circumstances. This really annoyed the Nikon astrophotography people
when they worked out what was going on because of course stars can look
just like hot pixels.
Note that this is different from dark frame subtraction, which some
cameras 'helpfully' do for you on long exposures.
(And then there is the issue that at some high ISO all cameras no
longer increase the ADC gain but just scale the RAW data digitally,
meaning that there is no image-quality point to increasing the ISO past
that point. Camera makers don't document what this point is for any
particular model, of course; photographers get to do the measurements
themselves. I believe it involves statistical analysis of RAW data to
see if there are suspicious gaps in the histograms.)
What cameras are really doing with sensor data, ADCs, and their RAWs
is a very deep rabbit hole. It's also probably not really relevant to
most photographers; my impression is that you have to really care about
fine details of technical image quality for this stuff to make any real
difference.
(Also, my general assumption is that if any particular thing had a
visible effect on image quality it would be quite well known. Today's
DSLR photographers pixel-peep quite a lot and are vocal about anything
that they can see.)
- cks
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