Even though they don't have that long a history compared to other gadgets available on the market, image scanners have evolved a lot since their beginnings, now being available as flatbed scanners, planetary scanners or digital camera scanners, with a wide variation of designs and functions.
The more common examples that are found in offices are variations of the flatbed (desktop) scanner, but hand-held scanners also have evolved from text scanning “wands” to 3D scanners, being more and more used in industrial design, reverse engineering, test and measurement, orthotics, gaming and other applications. Also available are mechanically-driven scanners that move the document and they are used for large-format documents, where a flatbed scanner would be impractical.
The key-element of modern scanners is that they use a charge-coupled device (CCD) or a Contact Image Sensor (CIS) as the image sensor, unlike older drum scanners, which use a photomultiplier tube as the image sensor. Other types of scanners are planetary scanners, which take photographs of books and documents, and the 3D scanners, which produce three-dimensional models of objects.
Also, there are digital camera scanners that are based on the concept of reprographic cameras, offering advantages such as speed, portability, gentle digitizing of thick documents without damaging the book spine. But new scanners have taken it a little further, combining 3D scanners with digital cameras to create full-color, photo realistic 3D models of objects.
How it all started
Scanners are considered to have evolved from the early telephotography input devices, which consisted of a rotating drum with a single photo detector at a standard speed of 60 or 120 rpm (later models up to 240 rpm). They sent a linear analog AM signal through standard telephone voice lines to receptors, which synchronously printed the proportional intensity on special paper.
This system was in use in press from the 1920s to the mid-1990s. Color photos were sent as three separated RGB filtered images consecutively, but this was used only for special events due to transmission costs.
The first image scanner ever developed was built in 1957, at the US National Bureau of Standards, by a team led by Russel Kirsch, and it was a drum scanner. The first image ever scanned on this machine was a 5 cm square photograph of Kirsch's then-three-month-old son, Walden. The black and white image had a resolution of 176 pixels.
From then on, scanners have slowly developed into the modern devices that we use today, going through a variety of models and several scanning technologies that have resulted into multiple types of image scanners.
Types of scanners
The drum scanners' particularity is that they use photomultiplier tubes (PMT) for the image capture, rather than charge-coupled device (CCD) arrays found in flatbed scanners and inexpensive film scanners. Reflective and transmissive originals are mounted on an acrylic cylinder, the scanner drum, which rotates at high speed while it passes the object being scanned in front of precision optics that deliver image information to the PMTs. Most modern color drum scanners use 3 matched PMTs, which read red, blue, and green light respectively. Light from the original artwork is split into separate red, blue, and green beams in the optical bench of the scanner.
It's not called a drum scanner for nothing, in case someone was wondering, but because of the large glass drum on which the original artwork is mounted for scanning. One of the unique features of drum scanners is the ability to control sample area and aperture size independently.
The sample size is the area that the scanner encoder reads to create an individual pixel. The aperture is the actual opening that allows light into the optical bench of the scanner. The ability to control aperture and sample size separately is particularly useful for smoothing film grain when scanning black-and white and color negative originals.
Only a few companies continue to manufacture drum scanners. While prices of both new and used units have come down over the last decade, they still require a considerable monetary investment when compared to CCD flatbed and film scanners. However, drum scanners remain in demand due to their capacity to produce scans that are superior in resolution, color gradation, and value structure. Also, since drum scanners are capable of resolutions up to 12,000 PPI, their use is generally recommended when a scanned image is going to be enlarged.
Even though flatbed scanners are more and more used in various operations, drum scanners continue to be used in high-end applications, such as museum-quality archiving of photographs and print production of high-quality books and magazine advertisements.
Flatbed scanners, also called desktop scanners, are the most versatile and commonly used scanners. They are usually composed of a glass pane(or platen), under which there is a bright light (xenon or cold cathode fluorescent), which illuminates the pane, and a moving optical array. This scanner allows the user to place a full piece of paper, book, magazine, photo or any other object onto the bed of the scanner and has the capability to scan that object.
Images to be scanned are placed face down on the glass, an opaque cover is lowered over it to exclude ambient light, and the sensor array and light source move across the pane, reading the entire area. An image is therefore visible to the detector only because of the light it reflects. Transparent images do not work in this way, and require special accessories that illuminate them from the upper side. Many scanners offer this as an option.
Film scanners work quite simply. Thus, uncut film strips of up to six frames or four mounted slides are inserted in a carrier, which is moved by a stepper motor across a lens and CCD sensor inside the scanner. Dedicated film scanners are often better than flatbed scanners, regarding the resolution, partly because they don't need to scan large areas.
Handheld scanners have two variations, namely document and 3D scanners. They use the same basic technology as a flatbed scanner, but rely on the user to move them instead of a motorized belt. This type of scanner typically does not provide good image quality. However, it can be useful for quickly capturing text.
Most hand scanners were monochrome, and produced light from an array of green LEDs to illuminate the image. A typical hand scanner also had a small window through which the document being scanned could be viewed. They were popular during the early 1990s.
Handheld 3D scanners are popular for many applications, such as industrial design, reverse engineering, inspection & analysis, digital manufacturing and medical applications.Interfaces
The interfaces that scanners use are Parallel, SCSI, USB and FireWire. Parallel is one of the more commonly used interfaces. Parallel scanners will be connected directly into the back of your computer and have an available pass-through port on the back for your computer printer to be connected to.
SCSI (Small Computer System Interface) is another popular connection for scanners. While the SCSI port will be much faster transferring data than a parallel port, it can sometimes be difficult for some users to install a SCSI card into their computer. USB scanners are easier to use and cheaper than SCSI devices, while FireWire is an interface that is much faster than USB1.1 and comparable to USB 2.0.
Although the evolution of scanners may not be as spectacular as that of TVs, let's say, important improvements have been added along they years and there's probably much more to come and change the face of scanning technology as we know it.