Image scanner

When the stylus makes contact with a raised part of the plate, it sends a pulse across a pair of wires to a receiver containing an electrode linked to another pendulum.

[4] In 1893, the American engineer Elisha Gray introduced the telautograph, the first widely commercially successful fax machine that used linkage bars translating x- and y-axis motion at the receiver to scan a pen across the paper and strike it only when actuated by the stylus moving across the transceiver drum.

[4] In 1902, the German engineer Arthur Korn introduced the phototelautograph, a fax machine that used a light-sensitive selenium cell to scan a paper to be copied, instead of relying on a metallic drum and stylus.

In Murray and Morse's initial design, the drum was connected to three lathes that etched cyan, magenta, and yellow (CMY) halftone dots onto three offset cylinders directly.

In this system, three color-separated plates (of CMY values) are prepared from a color negative via dot etching and placed in the scanner bed.

Each photocell connects to an analog image processor, which evaluates the reflectance of the combined CMY values using Neugebauer equations and outputs a signal to a light projector hovering over a fourth, unexposed lithographic plate.

In the 1950s, the Radio Corporation of America (RCA) took Hardy and Wurzburg's patent and replaced the projector-and-photocell arrangement with a video camera tube focusing on one spot of the plate.

The Bartlane system was initially used exclusively by telegraph, with the five-bit Baudot code used to transmit the grayscale digital image.

Reproduction of the image was achieved with a lamp passing over the punched holes, exposing five different intensities of light onto a film negative.

It employed a flatbed design with a continuous feed capable of scanning up to letter paper in 1-bit monochrome (black and white).

[15]: 53 [16] The Autokon 8400 enjoyed widespread use in newspapers—ECRM shipped 1,000 units to newspaper publishers by 1985[13]—but its limited resolution and maximum scan size made it unsuitable for commercial printing.

Four of ECRM's competitors introduced commercial flatbed scanners that year, including Scitex, Agfa-Gevaert, and Linotype-Hell, all of which were capable of scanning larger prints at higher resolutions.

The last Autokon was a wider format, online only device which utilised both a red and green laser to improve the response to the scanning of colour photographs.

[19] Designed by Andy Hertzfeld and released by Thunderware Inc., the ThunderScan contains a specialized image sensor built into a plastic housing the same shape as the ink ribbon cartridge of Apple's ImageWriter printer.

Based on a CCD imaging element, the Model 700 was capable of scanning letter-sized documents at a maximum resolution of 200 dpi at 1-bit monochrome.

[24][25] The first relatively affordable flatbed scanner for personal computers appeared in February 1987 with Hewlett-Packard's ScanJet, which was capable of scanning 4-bit (64-shade) grayscale images at a maximum resolution of 300 dpi.

[36][38] Some sheetfed scanners, called automatic document feeders (ADFs), are capable of scanning several sheets in one session,[39][40] although others only accept one page at a time.

Some other handheld scanners have switches to set the optical resolution, as well as a roller, which generates a clock pulse for synchronization with the computer.

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.

Chinon Industries patented a specific type of overhead scanner, which uses a rotating mirror to reflect the contents of the bed onto a linear CCD, in 1987.

Small portable scanners, either sheetfed or handheld and operated by batteries and with storage capability, are available for use away from a computer; stored scans can be transferred later.

[47][61] 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.

Because CCDs have a much greater depth of field, they are more forgiving when it comes to scanning documents that are difficult to get perfectly flat against the platen (such as bound books).

This data is then processed with some proprietary algorithm to correct for different exposure conditions, and sent to the computer via the device's input/output interface (usually USB, previous to which was SCSI or bidirectional parallel port in older units).

From 2000 all-in-one multi-purpose devices became available which were suitable for both small offices and consumers, with printing, scanning, copying, and fax capability in a single apparatus that can be made available to all members of a workgroup.

Typically, in addition to the scanning utility, some type of raster image editor (such as Photoshop or GIMP) and optical character recognition (OCR) software are supplied.

The color output of different scanners is not the same due to the spectral response of their sensing elements, the nature of their light source, and the correction applied by the scanning software.

Once on the computer, the image can be processed with a raster graphics editor (such as Photoshop) and saved on a storage device (such as a hard disk).

Preparation involves manually inspecting the papers to be scanned and making sure that they are in order, unfolded, without staples or anything else that might jam the scanner.

Technical difficulties arise from the books usually being bound and sometimes fragile and irreplaceable, but some manufacturers have developed specialized machinery to deal with this.