From: "Shel Belinkoff"
Subject: What Causes This?
http://home.earthlink.net/~scbelinkoff/SB_0010.jpg
What causes the horizontal stripes on the subject's arm?
Camera: istD
Hi Shel,
Possibly the two stops underexposed gives a clue in that we may well be
seeing posterisation when the bits are stretched as you compensate for the
underexposure, possibly combined with some shadow clipping in one or more of
the colour channels.
Underexposing is something to really avoid in the digital world but if the
original shot was taken in raw you may be able to do something in the raw
converter. The methods used to compensate for underexposure do directly
affect shadow detail, try these steps in the sequence given:
1) Push the exposure slider as far as you can until hints of highlight
clipping occur.
2) Back off the shadows slider if there is any shadows clipping.
3) Adjust brighness and then contrast for your desired tonality.
The important thing here is that we are using the exposure control for the
primary underexposure compensation rather than brightness. It is possible to
achieve much the same appearance the other way round but you get much
greater shadows posterisation because of the way these manipulations shuffle
the bits around.
If it was taken as jpeg rather than raw, there isn't much you can do.
Rob.
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