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Old August 7th 06, 03:44 PM posted to rec.photo.digital
Volker Hetzer
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Posts: 79
Default Measurung dynamic range...

wrote:
wrote:

Really measuring dynamic range is quite a difficult job.


In reading my post I see I really left out a lot, and didn't explain
myself very well. The problem is accurate radiometry/photometry.
Accurately measuring light is not a trivial problem- the instruments
are expensive and need frequent calibration. The big problem is
getting black references. White references are easy to do, and don't
need super accuracy. The problem is, what is the brightness, or even
reflectivity of a black reference.

I've got a light trap from basiccolor, so that's not much of a problem
for me. (Can't recommend it though, for EUR70 you get some cheap wood
and plastic stuff.)


To simplify the math, lets look at Black and White, say an 8 bit grey
scale. There can be up to 256 values in the image. But the best
available black inks or paints have a reflectivity of about 2-3%. If
we use a single even illumination, then a black and white printed chart
has a dynamic range of 50:1 or less. Thus, we can't use a printed
chart to test a camera with a dynamic range of 250:1 or 500:1.

I can do that by putting the stuff against a window in a darkened room or
even a box. Not sure yet.
What I will probably need is a large translucent grey slide too,
to embed the wedge in it and check different exposure settings like
center weighted or matrix or generally measuring exposure against the grey
and then compensating to get maximum range.

Lots of Greetings!
Volker