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Re: Digital Negatives with enough Tones for Pt/Pd
My advance apologies to those who wrinkle their noses when the list
ventures into this nerdy digital stuff.
Dan
Jeff said in his message...
>Each of my scans are scanned 12-bit and are 8-bit when saved by the
>scanner and when opened in Photoshop.
If your image enters Photoshop as an 8-bit image, you're aren't scanning
in 12 bits. What you are doing via the scanning software is choosing your
"best 8 bits" of image tonality. This might be OK for some images but
will not give you the best tonal capture in the long run.
There are two terms (actually more but lets address just these for now)
that describe a scanners ability to capture information:
Dynamic Range - you see figures like 3.2 or 3.5 for scanners. This is a
measurement of the density range that the scanner can accurately "see
into." The higher figures are important if you are scanning originals
with a high dynamic range, like Kodachrome slides. Scanning black and
white or color negatives by comparison is a cinch for the scanner to
handle dynamic range-wise.
Bit Depth - here you see figures like 8-bit, 10-bit, 12-bit etc. This
describes the number of tones that the scanner can differentiate. And
some scanners (like Jeff's apparently), though they have a "window" of
12-bits, will only let you take 8 bits (256 tones) into Photoshop. This
forces you to use the rudimentary scanner software to carefully select
the best 8-bits. A way around this type of scanner limitation is (as Jeff
has suggested) to scan the same negative more than once, biasing the
scanner software to capture the best shadow detail in one scan and the
best highlight in a second scan. You could take it further with more
scans as time, energy, anal compulsions etc. lead you (this is a poke at
myself, not at anyone else).
If your scanner will let you "take" all 12-bits into Photoshop (and
you'll know because Photoshop opens any image with more than 8 bits as a
16-bit image), there is no need or advantage to scanning more than once;
you've captured everything the scanner can handle. From there in
Photoshop you can work with the additional tonal steps to manipulate the
image with reduced chance of posterization.
Some imaging experts say that you should look for high dynamic range if
you are scanning slides and high bit depth if you are scanning negatives.
I think this is good advice. In an ideal world, your negatives would
perfectly match the dynamic range of the scanner. Since few of us are
making negatives with a density range of 3.5, we're having to STREEEEETCH
the captured tones to bring the scanned tones back to a pleasing image
that includes black and white. Having more bits lets us achieve this
stretching with much smoother tonal translation (see page 286 in "Making
Digital Negatives for Contact Printing" for an illustration that indeed
shows how a picture is worth a thousand words).
And a suggestion for Jeff who is disappointed by "banding" in the
highlights. Have you tried adding some Noise (Filter>Noise>Add Noise) in
Photoshop to just those parts of the image. This is an imaging trick
that's used to minimize banding when going to press too. You can easily
select just those values in your image using Color Range (Select>Color
Range). Apply Gaussian Noise with an amount of 3 (experiment to find what
amount works best) and you can eliminate lots of banding without
introducing artifacts or any apparent grittiness to your image.
Good luck!
Dan
Dan Burkholder
P.O. Box 111877
Carrollton, TX 75011-1877
USA
972-242-9819
fax 972-242-9651
danphoto@aol.com
www.danburkholder.com
Author of the book nobody should be without:
"Making Digital Negatives for Contact Printing."