Digital Prints

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Mastering Digital Printing
Scanning is done by scanners, and here’s how they work. Light generated in the scanner
itself is either reflected off or transmitted through a piece of art or film via a mirror-andlens
system (see Figure 3.1) and onto a grouping of light sensors, which are actually tiny
CCDs (charge-coupled devices) or in some cases CMOSs (complementary metal oxide
semi-conductors) or CISs (contact image sensors). The thousands of individual sensor elements,
one per image pixel, are either arranged in single or triple rows, called, respectively,
linear or tri-linear arrays.
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The scanner’s image is then formed (in the case of CCDs) like this: As the scan progresses line
by line down the original object, the light that is reflected or transmitted strikes each sensor,
which transfers that information in the form of increasing voltage to something called an A/D
(short for analog/digital) converter. The A/D converter then transforms the voltage into the
binary values (our favorite ones and zeroes) that are sent to the computer. Once inside the
computer, the scan is now a digital file that can be viewed, manipulated, and printed.
In the context of digital printing, the type and quality of a scan can be critical to the final
printed output. Therefore, let’s start off with an overview of some important things to
know about the scanning process. The types of scanners and what they do follows.
What You Need to Know about Scanning
There are some key issues about scanners and printers that need to be understood by anyone
hoping to become proficient with high-quality digital imaging and printing. These
issues or factors are: color depth, dynamic range, and resolution.
Color Depth
Remember our friend “Bit Depth” from the last chapter? Color depth is just another way
to say bit depth for scanners, and the same principles apply. A normal color original (print
or film) will require a minimum 24-bit scan (8 bits of information per RGB channel; all
scanners scan in RGB) to reproduce with adequate fidelity. This is the old “millions” scanner
setting (actually, it’s 16.8 million as we learned in Chapter 2). However, since some of
the scanned bits are invariably corrupted or lost to electronic noise, using a scanner with
a higher color depth like 36-bit is preferred. A 36-bit or “high-bit” scanner records 12 bits
per color channel, which translates into 68.7 billion possible values or colors per pixel.
Figure 3.1 Flatbed scanners use lamps,
mirrors, lenses, and sensor arrays to
produce digital files. The Creo iQsmart
has a unique inverted CCD sensor that
minimizes dust accumulation on the
CCD surface.
Courtesy of Creo