Scanning and Density

[Eric Goldstein <egoldste@xxxxxx>]

Sorry to be a bit behind...

a couple of days ago the question of why a flatbed scanner set up to
handle reflected paper positives yields weird results with chromes...
the answer is the difference in density range, also known as gamma.

Here are some broad ranges:

Depending on the quality and surface of the paper:
Black/white - from density 1.4 to 1.8
Color - from density 1.2 to 1.8

Depending on the make and quality of the slide film:
>From density 1.6 to 2.4

Color or B/W Negative:
up to and exceeding 4.0

Each stop is equivalent to a density increase of .3. As you can see and
as any experienced printer knows, there's a lot more contrast on the
negative than you can get on the paper.

With monitors/crts, gamma has a slightly different function, that of
expressing the correction for the non-linearity between input voltage
and the resulting brightness. Computer monitor standards usually have
you calibrate to about a gamma of 1.8. NTSC standard is 2.2. Check out:

http://www.vtiscan.com/~rwb/gamma.html


Eric G.