Digital BW, The Print

Hi George,

> There are a great many solutions to controlling contrast in digital
> photography that perform the same things as Zone System
> exposure and development used to. One of these is to expose
> for the shadows (making sure you get all the information) and
> then make 2 scans, one for the highlights and one for the
> shadows.

I don't believe what you outline here actually works.

No matter how many scans you make, you will get the EXACT same tonal range
information from the scanner.  When the scanner scans, it does nothing to
the image data, it just scans it.  The actual image data only occupies a
small portion of the scanner "space".  Subsequent scans will NOT change the
image data that was scanned.  I am talking strictly about commercial CCD
scanners.

> The range of densities, especially on Tri-X and color
> negative film allows us to capture detail that was previoiusly
> unprintable with only one scan. Tweaking the single scan with
> Levels and Curves destroys part of the image, even in 16-bit.

I've done thousands and thousands of scans, and have not seen this "problem"
you claim here.  Whether the image data is 16 bits or not isn't the issue,
it's whether the image data is spread out OVER the 16 bits.  Setpoints MUST
be done first to spread out the image data, then tonal curves.  Also, you
may or may not "combine" data values (which is what you mean by "destroy")
it depends on the "amount" of the tonal correction.  Also, combining,
depending on how severe, may simply not matter, as you only need 256
resultant tones in the final output.

> With 2 scans, one for the highlights and one for the shadows,
> you can then recombine these images in Photoshop using this
> procedure and get a nearly flawless Dynamic Range:

Unless you change "something" when you make the raw scans, the raw scans
from the same negative are identical.  What, on earth, is it you believe you
can change to "scan for the highlights and then scan for the shadows"???

Also, even if you did change exposure, which is the only thing you can
change, you STILL get the exact same range of image data.  Whether it falls
from .1 to 1.7 or from .2 to 1.8.  All exposure time (and aperture) does is
moves the density range of the image being scanned within the scanner
"space".

> Another, and more productive way,  is to combine 2 images
> taken in camera on a tripod

IF the images are exposed differently, this will work, but this is an
entirely different situation than you describe above.

Regards,

Austin