Digital Prints

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Mastering Digital Printing
they only allow it to be stored. Just like a large wallet is needed to hold a great sum of money,
but having a large wallet does not necessarily mean the wallet is full of money.”
There are actually two different, but related, types of dynamic range. There’s scene dynamic
range, which is how much tonal information an input process or medium can capture. It
usually applies to camera systems, and it’s expressed in terms of photographic exposure
value or f-stops. Color reversal film, for example, has a scene dynamic range of 7 f-stops.
Then there’s density range, which is the difference in density between the lightest and darkest
areas of an image. It’s the numerical range from the minimum density (Dmin) to the
maximum density (Dmax). If the Dmin is 0.3 and the Dmax (also called optical density)
is 3.9, then the density range is 3.6 D.
Density range applies to digital input devices like scanners, but it can also describe imaging
material, such as printing paper or photographic film. Reversal film (transparencies),
for example, has a wide density range (3.3–3.6 D) but a narrow dynamic range (7 f-stops).
Anyone who works with slides quickly realizes that, while the blacks are black and the
whites are bright, the shadows and highlights are very compressed. Slides are great for viewing
or projecting (what they were invented for), but for capturing all the subtle tones in a
scene, negative film, with its wider dynamic range but lower density range (2.4 D–3.0 D),
is much better. Other types of art materials also have their own inherent density ranges.
Photographic prints have an average range of around 2.0 D; watercolors, even less.
How does all this affect scanning? Several ways. First, you need to make sure you consider
what type of art you will be scanning before deciding on a scanner to purchase or a service
to use. And for that, density range and D values are important factors. When dealing
with transparencies with very dense blacks, you’ll want the widest density range and the
highest Dmax you can get so you can pull out the details from those dense areas. But with
certain kinds of reflective art, it’s not as critical because the prints themselves have a low
density range, and many low- to mid-priced scanners will do the job. (Unfortunately,
because of a lack of standards, advertised density ranges and Dmax specs, as with “resolution”
on inkjet printers, serve mostly marketing purposes. Use them to compare scanner
models by the same manufacturer, but be leery of any cross-brand comparisons. In fact,
comparative price at a given time is usually the best indicator of scanner performance.)
Scanner Resolution
I’ve saved the best for last. Or I should say, the most complicated. Some of this necessarily
overlaps what was discussed in the last chapter about image and printer resolution, but
I’m adding another piece of the resolution puzzle.
Most of the sales information for scanners highlights the dots-per-inch (dpi) resolution.
Technically, there are no dots in scanning, just samples. It should really be “samples per
inch” (spi) or pixels per inch (ppi), but that battle of terminology has been lost to the scanner
industry. Whenever you hear anyone mention dpi in the context of scanning (as I tend
to do), understand that they are also saying ppi. It’s still about pixels.
The more sensor elements per unit area, the higher the optical resolution of the scanner, and,
in general, the more information and detail the scanner is capable of capturing. Flatbed
scanners use the same naming system as inkjet printers to trumpet their resolutions:
2400×4800 dpi, for example. In this case, 2400 means the number of CCD elements across