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16-Bits Grayscale Scanning of
Ansel Adams' "The Tetons - Snake River"
How we obtained this scan. Not being able to control the quality of the scans from National Archives vendors, we chose to have one of the vendors scan the Adams' copy negative using a scanner that was capable of doing 16-bits per channel (a 48-bits scanner). By ordering a "raw" 16-bits grayscale scan, we could then pick the best 8-bits, rather than letting less experienced vendor technicians make that judgement for us. Although the vendor we chose did not use an Epson Perfection 3200 PHOTO Scanner, the scan is still suitable for this demonstation on the benefits of 16-bits per channel (vs. standard 8-bits per channel scanning).
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| Viewing our raw 16-bits scan. This scan, from an 8" x 10" copy negative (via the National Archives), lacks contrast and does not have any true black values or pure white values. |  |
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Opening our image file in Photoshop, we see under the "Image > Mode" menu that it is a 16-bits per channel grayscale image.
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Going to the "Image > Adjust > Levels" menu we can see a histogram of our image. |
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 | Adjusting the input levels. The next step is to adjust the input levels by setting a proper "black point" level (moving the black triangle from the left until it is directly under where the image begins to start changing in tonal values).A similar input adjustment is made to set a new "white point", using the white triangle. Making these two levels adjustments has taken us from "0" to a new black point input of "73", and from "255" to a new white point input of "215". Our image now has the proper contrast range and a true white and black. |
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| New Levels Histogram. If we save our levels adjustments by clicking the "OK" button, then bring up the Levels menu again, we'll see a newly written histogram that looks properly adjusted. We can now go to the "Image > Mode" menu and convert our image to "8-bits per channel" and retouch it to remove dust and scratches. |  |
| Compare to an 8-bits image. However, had we started out with an 8-bits grayscale image instead of a 16-bits grayscale image, the Levels histogram to the right would have been the result of all our Levels input adjustments. Notice the white spaces in this histogram? You've probably seen these before. They indicate the cloned or interpolated data that Photoshop has had to add to our image to make up for the lost tonal values, when we went from 0 to 73 to set a new black point, and from 255 to 215 to set a new white point -- a loss of 113 shades of gray! |  |
A 16-bits per channel Adjustment. What we've done is taken an image that had these gray vaues...
...and adjusted it to this proper grayscale:
An 8-bits per channel Adjustment. But had we started out with an 8-bits scan, our grayscale would have look like this after making our Levels adjustments:
We've taken out the dithering, so you can see the banding that results when you only have 143 tonal values left (256 minus 113). The reason the 16-bits scan file retains its quality is because it starts out with a possible 65536 tonal shades* per channel -- allowing one to throw out most of those values still leaves one with much more than 256 (the maximum number of values in an 8-bits per channel image file).
*Actually, in our original 16-bits grayscale scan of the Tetons, there were only about 572 tonal values, but even after our Levels adjustments, there still remained much more than 256 tonal values left -- without Photoshop having to result to the interpolation and cloning of values. These extrapolated or interpolated values cause blockiness, chalkiness, banding and loss of highlight and shadow detail within an image.
TIP: A poor man's answer to 16-bits grayscale scanning. If you don't have a 48-bits scanner that is capable of also doing 16-bits grayscale scanning, you can cheat and obtain a little more image information by scanning grayscale images in the RGB mode (24-bits). Once you've acquired the image file in Photoshop, make all your "Image > Adjust" changes (i.e. "Levels" and "Curves") BEFORE you convert the image to a grayscale. This does retain a little more tonal information than making all your adjustments on an 8-bits grayscale image.
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Obtaining Ansel Adams' prints or scans from the National Archives. The prints that Ansel Adams sold to the Interior Department are now in the National Archives. They are in the public domain, and part of our national heritage. 8" x 10" and 4" x 5" copy negatives have been made of from some of the more popular Adams prints (before they become too damaged by use) by the National Archives. Prints or digital scans can be ordered from the prints or copy negatives, using one of the National Archives' six authorzed vendors. For information on obtaining prints or scans of Ansel Adams images in the National Archive, contact us at Ansel_Adams_Archive@tssphoto.com. NOTE: The images on this web site are independent of and not authorized by the Ansel Adams Publishing Rights Trust, which controls the reproduction from Ansel Adams' original negatives and prints not held by the National Archive.
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History and heritage of Ansel Adams' early work
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