Computer scanner

A computer scanner (scanner comes from the English language scanner) is a peripheral that is used to "copy", by using the light, printed images or documents in digital format (color or black and white). The scanner was born in 1984 when Microtek created the MS-200, the first black and white scanner that had a resolution of 200dpi. This scanner was developed for the Apple Macintosh. Scanners may have accessories such as an automatic sheet feeder or an adapter for slides and transparencies.

Scanner Fujitsu

When obtaining a digital image, defects can be corrected, a specific area of the image can be cropped or text can also be digitized using OCR techniques. These functions can be carried out by the device itself or by special applications.

Today it is common to include the printer and the scanner in the same device. They are the so-called multifunction printers. Using the camera of smartphones as a scanner is also emerging.

Scanner quality

The data obtained by the scanners has a certain algorithm applied to it and is sent to the computer via an input/output interface (usually SCSI, USB, or LPT on pre-USB machines). The depth of the color depends on the characteristics of the scanning vector (the first of the basic characteristics that define the quality of the scanner) which is normally at least 24 bits. Images with greater color depth (more than 24 bits) are useful during digital image processing, reducing posterization.

Another of the most relevant parameters of the quality of a scanner is the resolution, measured in pixels per inch (dpi). Scanner manufacturers instead of referring to the actual optical resolution of the scanner, prefer to refer to the interpolated resolution, which is much higher thanks to software interpolation.

To make a comparison between types of scanners, better ones went up to 5400 dpi. A drum scanner had a resolution of 8,000 to 14,000 dpi.

The third most important parameter to provide quality to a scanner is the density range. If the scanner has a high density range, it means that it is capable of reproducing shadows and highlights with a single pass. They are devices in charge of incorporating the reality of the two dimensions, digitizing it, into a computer.

Computer connection

Multifunctional Epson

The size of the file where a scanned image is saved can be very large: a 24-bit quality image a little larger than A4 and uncompressed can occupy about 100 megabytes. Today's scanners generate this amount in a few seconds, which means you would want as fast a connection as possible.

Before scanners used parallel connections that couldn't go faster than 70 kilobytes/second, SCSI-II was adopted for professional models and although it was somewhat faster (a few megabytes per second) it was considerably more expensive.

Today the most recent models are equipped with USB connection, which have a transfer rate of 1.5 megapixels per second for USB 1.1 and up to 60 megapixels per second for USB 2.0 connections, which greatly eliminates the neck bottle that was had at the beginning. The two existing standards for interfaces on the market for Windows PCs or Macs are:

• TWAIN. Originally used for domestic or low-cost use. It is currently also used for large volume scanning.
• ISIS. Created by Pixel Translations, which uses SCSI-II, it is used in large machines for companies.

Output data

Scanning results in an uncompressed RGB image that can be transferred to your computer. Some scanners compress and clean the image using some kind of embedded firmware. Once the image is on the computer, it can be processed with an image processing program such as Photoshop, Paint Shop Pro or GIMP and can be saved to any storage unit such as the hard drive.

Scanned images are typically saved as JPEG, TIFF, Bitmap, or PNG format depending on what you want to use the image for later.

Note that some scanners are used to capture editable text (not just images as seen so far), as long as the computer can read this text. This process is called OCR (Optical Character Recognition).

Scanning a document

Document scanning is different from image scanning, although it uses some of the latter's techniques. Although document scanning can be done on general purpose scanners, most of the time it is done on special scanners dedicated for this purpose, made by Canon, Fujitsu or Kodak among others. Document scanners have larger feed trays than normal photocopiers or scanners.

They usually scan at a lower resolution than normal scanners, from 150 dpi to 300 dpi, thus avoiding excessive file sizes.

The scan is done in grayscale, although it is possible to do it in color. Most are capable of double-sided scanning at full speed (20 to 150 pages per minute). The most sophisticated have built-in firmware that "cleans" the scan by removing accidental marks. Data scanned on the fly is usually compressed.

Most scanned documents are converted into editable files using OCR technology. Using the ISIS and TWAIN drivers, the document is scanned in TIFF format, to pass the scanned pages to a word processor, which stores the corresponding file.

Scanning books involves additional technical difficulties. Some manufacturers have developed special scanners for this purpose, even making use of special robots in charge of turning the pages.

Types

The main types of scanners are drum, flat (which in turn can be CCD scanner or CIS), film or slide, handheld and mobile phone camera.

Hand Scanner

Handheld scanners come in two forms: document scanners and 3D scanners. Handheld document scanners are handheld devices that are dragged across the surface of the image to be scanned. Scanning documents in this way requires a steady hand, so uneven scanning speeds could produce distorted images - a little light on the scanner would indicate that the movement is too fast. They usually have a 'start' button, which is pressed by the user for the duration of the scan; some switches to adjust the optical resolution, and a roller, which generates a clock pulse for synchronization with the computer. Most scanners have a small window through which you could view the document being scanned. Also, they have a USB port, they usually save the result directly in JPEG format, on a microSD card that is usually up to 32 GB at least.

Flatbed scanner

Flatbed scanners are the most common, and are used to copy documents, single sheets, and photos of various sizes, up to a maximum size (usually one sheet of Letter, Legal, or Oficio size). It features several improvements over handheld scanners, such as a significant increase in scan quality (optical resolution) and speed.

Rotary (or Drum) Scanner

Widely used in graphic or artistic design studios, mainly due to their high optical resolution, they are large and allow scanning by CYMK or RGB color models.

Scanner app

The higher-resolution cameras installed in some smartphones can scan documents of reasonable quality by capturing a photo with the phone's camera and post-processing it with a scanning application, whether to whiten the background of a page, correct perspective distortion in order to fix the rectangular shape of the document, convert to black and white, etc. Some applications can scan multi-page documents with camera exposures in succession and generate a single file document or multi-page files.