Types of Scanners

Types of Scanners

Drum Scanner

Drum Scanner

            Drum scanners capture image information mostly with photomultiplier tubes (PMT), rather than the 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 three 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."[3] Photomultipliers offer superior dynamic range and for this reason drum scanners using photomultiplier tubes can extract more detail from very dark shadow areas of a transparency than flatbed scanners using CCD sensors. The smaller dynamic range of the CCD sensors, versus photomultiplier tubes, can lead to loss of shadow detail, especially when scanning very dense transparency film. Some DeskTop Publishing drum scanners use cheaper illumination/sensor systems than PMT such as halogen lamps and photodiodes, which have their dynamic range less than that of photomultipliers but higher than that of charge coupled devices.

            The drum scanner gets its name from the clear acrylic cylinder, the drum, on which the original artwork is mounted for scanning. Depending on size, it is possible to mount originals up to 20"x28", but maximum size varies by manufacturer. "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."

            While drum scanners are capable of scanning both reflective and transmissive artwork, a good-quality flatbed scanner can produce good scans from reflective artwork. As a result, drum scanners are rarely used to scan prints now that high-quality, inexpensive flatbed scanners are readily available. Film, however, is where drum scanners continue to be the tool of choice for high-end applications. Because film can be wet-mounted to the scanner drum and because of the exceptional sensitivity of the PMTs, drum scanners are capable of capturing very subtle details in film originals.

Drum Scaner

             The situation as of 2014 was that only a few companies continued to manufacture drum scanners. While prices of both new and used units dropped from the start of the 21st century, they were still much more costly than CCD flatbed and film scanners. Image quality produced by flatbed scanners had improved to the degree that the best ones were suitable for most graphic-arts operations, and they replaced drum scanners in many cases as they were less expensive and faster. However, drum scanners with their superior resolution (up to 24,000 PPI), color gradation, and value structure continued to be used for scanning images to be much enlarged, and for museum-quality archiving of photographs and print production of high-quality books and magazine advertisements. As second-hand drum scanners became more plentiful and less costly, many fine-art photographers acquired them.

Flatbed

             

This type of scanner is sometimes called reflective scanner because it works by shining white light onto the object to be scanned and reading the intensity and color of light that is reflected from it, usually a line at a time. They are designed for scanning prints or other flat, opaque materials but some have available transparency adapters, which for a number of reasons, in most cases, are not very well suited to scanning film.

Flatbed Scanner

CCD scanner

            "A flatbed scanner is usually composed of a glass pane (or platen), under which there is a bright light (often xenon, LED or cold cathode fluorescent) which illuminates the pane, and a moving optical array in CCD scanning. CCD-type scanners typically contain three rows (arrays) of sensors with red, green, and blue filters."

CCD Scanner

CIS scanner

              Contact image sensor (CIS) scanning consists of a moving set of red, green and blue LEDs strobed for illumination and a connected monochromatic photodiode array under a rod lens array for light collection. "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."

CIS scanner

Film

Film scanner

            This type of scanner is sometimes called a slide or transparency scanner and it works by passing a narrowly focused beam of light through the film and reading the intensity and color of the light that emerges. "Usually, 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. Some models are mainly used for same-size scans. Film scanners vary a great deal in price and quality." The lowest-cost dedicated film scanners can be had for less than $50 and they might be sufficient for modest needs. From there they inch up in staggered levels of quality and advanced features upward of five figures. "The specifics vary by brand and model and the end results are greatly determined by the level of sophistication of the scanner's optical system and, equally important, the sophistication of the scanning software."

Roller scanner

              Scanners are available that pull a flat sheet over the scanning element between rotating rollers. They can only handle single sheets up to a specified width (typically about 210 mm, the width of many printed letters and documents), but can be very compact, just requiring a pair of narrow rollers between which the document is passed. Some are portable, powered by batteries and with their own storage, eventually transferring stored scans to a computer over a USB or other interface.

Roller scanner

3D scanner

3D scanners collect data on the three-dimensional shape and appearance of an object.

3D scanner

Planetary scanner

Hand

Hand scanners are moved over the subject to be imaged by hand. There are two different types: document and 3D scanners.

Hand document scanner

              "Hand held document scanners are manual devices that are dragged across the surface of the image to be scanned by hand. Scanning documents in this manner requires a steady hand, as an uneven scanning rate produces distorted images; an indicator light on the scanner indicates if motion is too fast. They typically have a "start" button, which is held by the user for the duration of the scan; some switches to set the optical resolution; and a roller, which generates a clock pulse for synchronization with the computer. Older hand scanners were monochrome, and produced light from an array of green LEDs to illuminate the image";[8] later ones scan in monochrome or color, as desired. A hand scanner may have a small window through which the document being scanned could be viewed. In the early 1990s many hand scanners had a proprietary interface module specific to a particular type of computer, such as an Atari ST or Commodore Amiga. Since the introduction of the USB standard, it is the interface most commonly used. As hand scanners are much narrower than most normal document or book sizes, software (or the end user) needed to combine several narrow "strips" of scanned document to produce the finished article.

Inexpensive portable battery-powered "glide-over" hand scanners, typically capable of scanning an area as wide as a normal letter and much longer, remain, available as of 2014.

Hand 3D scanner

               Handheld 3D scanners are used in industrial design, reverse engineering, inspection and analysis, digital manufacturing and medical applications. "To compensate for the uneven motion of the human hand, most 3D scanning systems rely on the placement of reference markers, typically adhesive reflective tabs that the scanner uses to align elements and mark positions in space."

Portable

              Image scanners are usually used in conjunction with a computer which controls the scanner and stores scans. Small portable scanners, either roller-fed or "glide-over" hand-operated, operated by batteries and with storage capability, are available for use away from a computer; stored scans can be transferred later. Many can scan both small documents such as business cards and till receipts, and letter-sized documents.

portable

Smartphone scanner apps

            The higher-resolution cameras fitted to some smartphones can produce reasonable quality document scans by taking a photograph with the phone's camera and post-processing it with a scanning app, a range of which are available for most phone operating systems, to whiten the background of a page, correct perspective distortion so that the shape of a rectangular document is corrected, convert to black-and-white, etc. Many such apps can scan multiple-page documents with successive camera exposures and output them either as a single file or multiple page files. Some smartphone scanning apps can save documents directly to online storage locations, such as Dropbox and Evernote, send via email or fax documents via email-to-fax gateways.

Smartphone scanner apps

             Smartphone scanner apps can be broadly divided into three categories: 1) document scanning apps primarily designed to handle documents and output PDF, and sometimes JPEG, files, 2) photo scanning apps that output JPEG files, and have editing functions useful for photo rather than document editing; and 3) barcode-like QR code scanning apps that then search the internet for information associated with the code.