Re: [APML] New Epson Scanner

[Roland Roberts <roland@astrofoto.org>]

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>>>>> "Vicent" == Vicent Peris <vicentperis@ya.com> writes:

    Vicent> As I understand, the maximum dynamic range is limited by
    Vicent> the bits per channel. If you have two lights, one 1000
    Vicent> times brighter than the other, you won't see the dimmer
    Vicent> light because it is on the level "0.256" (supposing the
    Vicent> brighter one is on the level 256). Thus, an image with
    Vicent> 8bit/channel will have only a dynamic range of 2.4.

Not exactly.  The dynamic range is a measure of the *range* of
brightnesses which can be distinguished by the scanner, not how many
discrete levels it can produce.  One can imagine a pathologically bad
scanner which has 48-bit color (16-bit/channel) but can distinguish
only in the range of light gray to pure white.  Within that range, it
has wonderful discrimination, but everything darker than light gray
shows up as black.

There are now scanners really as bad as all that, but the example
serves the purpose of illustrating that dynamic range has to do with
*physical* brightness levels, not digitized levels.  One can speak of
the dynamic range of film and slides independent of any digitization
of the images.  My understanding is that the term originates from
measurements of film densities, but I'm not clear on how the scale is
calibrated....

regards,

roland
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Roland B. Roberts, PhD                             RL Enterprises
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roland@astrofoto.org                           Brooklyn, NY 11220

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