Re: [APML] Fw: images

["Rick Kellogg" <rkellog1@twcny.rr.com>]

Chuck,

You are "confusing" the innate recording bit level of film with its useful
range needed for recording what you are interested in.

The bit level of film, refers to its ability to record.  What you are
showing here is how many bits of detail there are in the "desired" part of
the image.  Now its true, that with clever settings of the scanner, you
probably could have gotten this detail out of the negative with only an 8
bit scanner, but to say that film can record detail to only 4-5 bits is not
correct.

There is "unwanted" (for your application) detail in the part of the scan
that you threw away when you contrast stretched.  A quantitative measure of
films bit recording capability would be to measure a gray scale from dmin
to dmax, and do a similar kind of test.

Try your test again, but set your scanner so that dmin is < full scale
counts, and dmax is > 0 counts.  Limit the number of bits in the scan, and
see how many bits you need.  I suspect it's 11-13.

Also don't forget that 16 bit files of CCD record linear counts.  The 8 bit
files of photoshop use a gamma of 2.2, so it can store a large dynamic
range.

Rick Kellogg

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