The Scanner - a device for translation of the scene with paper carrier in digital, computer format. The Suppressing majority scanner is used for preparing and publishing different information material at present i.e. consumers are interested, mainly, in facility of the processing the scenes and text. Some scanners are successfully used in CAD, but, as a rule, corresponding to systems have a more narrow profession. At present broad using scanner is forecasted in the field of fax relationship though here remains else much undecided questions.

As likely as not that application scanner can become the systems of keeping and searching for графичиской to information, in which material is kept in the form of the scenes (the mines) integer pages, but неотдельных of the lines to text information. Herewith remain unchangeable both format of the page, and any graphic scenes (the drawings, illustrations, graphs and etc.). the similar systems wholly can become the important component part a knowledgebase. Is Not excluded that exactly they will define the future scanner in combination with personal computer.

General principles

The Scanners read with papers, films or other hard carriers analog texts or scenes and will convert them in digital format. They serve everywhere: in large office, where are processed enormous archives document, in the publishers and design-design organization, as well as in small company and home office. Insofar broad sphere of the using scanner, so much their varieties. The Price of the scanner can form from several groups of ten before group of ten of a thousands of the dollars, optical permit - from 100 before 11000 points on inch (in english dpi, dot per inch), but velocity of the scan - from 1-2 before 80 s./min.

For performing that or other concrete problems suitable nowhere near not each model. As a rule, fitness of the scanner is defined by collection his(its) technical parameter: constructive type, format, permit, depth of the colour, range of absorbances and etc. The Permit ("input permit", or "permit at scan") measures density to information, introduced by device on linear inch at digitization of the scene.

If more simply, this amount pixel, which scanner "will see" in one inch of the source material (the photographies, slide and pr.). The Majority scanner allow use the variable input permit, and, assigning that or other value in dpi (dots per inch - a points on inch) or ppi (points/pixels per inch - a points/pixels on inch), we shall assign the amount of the pixels, on which scanner is done linear inch of the scene.

The Desk scanners contains the source of the light, lens, instrument with зарядовой by relationship (PZS) and one or several analog-to-digital converters (ACP). All elements PZS are situated in row - on one element for each pixel of the line of the unrolling. If beside you there is 300 elements PZS on each inch along line of the scan, that greatly possible optical permit forms 300 dpi. If on each inch along line of the scan happens to 600 elements PZS, that greatly possible optical permit forms 600 dpi.

Two permits sometimes exists Beside scanner. One less, it is identified optical, but other - more, it is identified interpolated and his(its) often write on box, attracting trustful buyer greater numeral. The Real permit of the scanner is exactly optical since this - a most high permit, which capable to realize his(its) optical system. That is to say if it is 600 dpi, this means that scanning head of the scanner capable to do not more than 600 steps on inch, and, accordingly, "see" in him not more, than 600 pixels. Interpolated permit usually in two - four times more optical. But in mode of the interpolations scanner does not enter additional given - getting same 600 pixels, he creates between them new, mathematically calculating for them importances of the tone and brightness.

In technical given professional models scanner stress is done on optical permit since using him(it), rather then interpolated, possible оцифровать scene with maximum quality. The Option scaling, realized in ensemble of the programs of the scan - at all not output from position, but the whole only instrument for reception of the scene of the necessary amount under the known necessary входном permit.

The Scan of the scene is executed line by line. The Bunch of the light is reflected from dartboard and through lens gets on PZS. Each PZS will convert the light in analog voltage (hanging from intensity of the light), defining level sulphur for one pixel. In ACP analog voltage is converted in digital importance with use 8, 10 or 12 bits for each (main) of the colour.

The Advantage of the presentation of each colour by large number bit understandable - than more their number, that step of the transition less from tone to tone, and such transition become so small that imperceptible for eye of the person. In turn, this leads to removal постеризации - a sudden change the colour when turning from one pixel to the following, when must be reproduced fluent change the colour. Besides, at presence corresponding to other component of the scanner, additional bits allow to distinguish more details in dark area.

One more important moment, to which follows to call attention: all declared by manufacturer bits, are used in scanner for presentation level sulphur. After all some manufacturers can comprise of specification bits calibrations for the reason преукрасить features of the scanner.

Fortunately determination of the required number bit does not cause the difficulties. If you do not be going to too often to scan to photographies, that 24-bit presentation will be sufficient. Under regular scan photography or artistic drawing you will take 30-bit presentation for the best transfer of the details in dark area. Need in 36-bit presentation, colour can appear in that event only if you often work with диапозитивами. For transparent carrier диапозитива typical broader (in contrast with imprint on paper) range density and in this case additional bits will allow to send more details in dark area.

Portable scanners

Portable or manual scanners provide the inexpensive way of the transformation of the scene in digital form and their entering in computer. In contrast with desk scanner they possess vastly more modest possibility, for instance, they unfit for use in desk publishing system, additionally the most slightest vibration, допущенная in process of the manual scan, brings about devaluation of the done work. But then and cost(stand) such scanners vastly more cheaply. Their wholly possible use where is not required high quality of the scene.

The Kit of the supply of the scanner comprises of itself software, which gives a chance editing, record on disk and conclusion on seal the scenes. Work with device does not require the person a skill. The Scanned original fits on flat surface, scanner is fixed on one of the sides of this original and, after striking the button of the starting, slowly moves on original manually. On measure of the moving the scanner on original possible to stake out that that is got. The Majority portable scanner has a big window for viewing, through which is seen processed original. Some devices provide reproduction got in process of the functioning(working) the scene on screen of the personal computer. The Maximum width of the scanned original forms 2.5 inch (6.4 refer to) and is limited by size worker to surfaces of the device. The Length of the original depends on memories of the computer. If original exceeds the length of the scanner, that possible processes his(its) separate parts, but then, by means of program, unite these part in one scene.

The Sensors can generate 4-bit data, corresponding to 16 tones of the scale to brightness (the sulphur of the scale). Usually scene, scanned such scanner, is intended for entering on lazer printer, which can not directly print the tone by sulphur of the scale (i.e. all tone from black before white colour). So scanner must send got information on personal computer, which program executes processing the scene for output him(it) on printer. In that events, when scanner provides only black and white points, lazer printer easy works with him.

Desk scanners

Exists three varieties desk scanner:

• flatbed
• рулонные
• projection

The Main difference flatbed scanner is that their scanning head moves for papers by means of crossbar engine. The Similar scanners - it is enough expensive device, but, probably, and most "capable". Outwardly they than-that can remind some types of the copying machines. For scan of the scene necessary to open the lid of the scanner, place the scanned sheet on glass plate by scene downwards whereupon close the lid. All are the most further control process scans is realized with keyboards of the computer - when work with one of the special programs, delivered with such scanner. Understandable that considered a design of the scanner allows to scan not only separate sheets, but also pages of the journal or books.

Functioning рулонных scanner reminds functioning common fax-machines. The Separate sheets document stretch through such device, herewith and is realized their scan. In this instance scanning head stays put, but already comparatively she moves the paper. Understandable that in this case copying of the pages of the books and journal simply impossible. The Considered scanners it is enough are broadly used in area, in accordance with optical recognition symbol OCR (Optical Character Pecognition). As a matter of convenience functioning(working) рулонные scanners are usually equiped device for automatic presenting the pages.

The Projection scanners most of all remind своеобразный projection device. The Introduced document to place on surface of the scan by scene upwards, block of the scan is found herewith also upstairs. Moves only scanning device. The Main particularity data scanner is a possibility of the scan projection three-dimensional subject.

Drum scanners

The Drum scanners, on actinism, vastly exceeding consumer flatbed device, are used in printings solely, where is required high-quality reproduction professional photogaph. The Permit such scanner usually forms 8000-11000 points on inch and more.

In drum scanner originals take seats on internal or external (depending on models) to side of the transparent cylinder, which is identified the drum. Than more drum, that more area to his(its) surfaces, on which is assembled original, and accordingly, that more maximum area of the scan. After montage of the original drum happens to in motion. One line of the pixels is read For one his(its) turn so process of the scan much reminds work turning-винторезного tool. Passing through slide (or reflected from opaque original) narrow ray light, which s the powerful lazer, by means of systems mirror gets on FEU (фотоэлектронный multiplier), where is digitated.

CCD and CIS scanners

The Base of each scanner is a point-to-point block, which consists of the source of the light, photocell and optical system. The Light, reflecting from original, through optical system gets on photocells so occurs the scan. The most wide-spread flatbed scanners produced at present, on type reading element are divided on two categories: on base CCD (Charge Coupled Device, instrument with зарядовой by relationship PZS) and CIS (Contact Image Sensor, contact sensor of the scene}.

In CCD-scanner as source of the light is used lamp with cool cathode. This type of the lamps allows to get the even light flow with stable feature that provides the correct issue a colour at scan. For issue of the light, reflected from original, фотоприемнику is used optical system, comprising of itself lens and system mirror.

The lens and system mirror are absent In CIS-scanner. To account this greatly decreases the sizes and weight device. The Source of the light serves the straightedge a led, but photocells tightly adjoin to glass. In contrast with CCD-scanner beside CIS-scanner on order smaller depth to sharpnesses, worse differ the tone. Moreover, dynamic range CIS-scanner decreases on the one third in 500 business hourses of the scanner approximately, but CCD-scanners work before 10000 hours without observable deterioration of the features. The most essential pro CIS-scanner this their low price, which is explained by relative simplicity of the fabrication.

Dynamic range of the scanner

The Dynamic range of the scanner is measured on logarithmic scale from 0 (the absolute transparency) before 4,0 (absolute blackenning surface). These numbers have importance only then, when you necessary high-quality scan or you plan to scan the big amount a slide. As a rule, for photography or other flat subject (the opaque original) is not required density of the scanner above 2,2. In most cases for such work wholly it is enough importances 2,0. However for reception high-quality result at scan slide or film (the transparent original) you will need scanner with dynamic range beside 3,2. Follows to call attention that scale of the measurement, either as сейсмографическая scale Rihtera, is logarithmic so original with density 3,0 D темнее of the original with density 2,0 D in 10 once. Accordingly, importance 3,3 D corresponds to double more dark scene, than 3,0 D.

Alongside with physical allowing ability important standard of judgement is considered absorbances, which means that scanner can distinguish that or other shades of gray original scene. Theoretically 12-class scanner can distinguish more tone, than 8-class, however, big depth of the colour - not yet proof to high absorbances. Density inexpensive device, as a rule, does not communicate in instruction; beside professional device this factor is 3,0 or above.

The Purpose of the scanner in that to as possible more exactly send the paints of the original. The Monochrome документные scanners work in two color modes: monochrome (1 bit/pixel; for the best suits for scan stroke drawing and text) and in sulphur halftone (8, 10 or 12 bits/pixel). In colour scanner to he are added third - полноцветный RGB-mode (24, 30 or 36 bits/pixel). The Device with depth of the colour 24 bits can distinguish 16,7 mln. tone. The Human eye, perceiving as much as color tones, unable to catch the difference between scenes, got by means of 24- and 36-class scanner.

From what depends the quality отсканированных scenes?

Certainly, the most important feature of any scanner - a quality of the got scenes. Understanding that, what factors render most deep influence on quality of the scene, will help not only to take the motivated decision when buying, but also to the ful use the possibility of the gained scanner. Tops the list color balance i.e. ability to fix the neutral colour in neutral form. If цветном scan to monochrome photography resulting scene turns out to be mildly painted, that possible argues that colour on your colour photography will also be unchancy. Is it Closely connected with this feature correctness цветопередачи, or ability to fix the colour greatly to original close.

If at the time of, when is entered scene, already known final sizes to illustrations and parameters excretory device, that cost(stand)s to choose such input permit, under which will is incorporated exactly that volume to information, which necessary. This will allow not to resort to accompaniment or subtraction to information from scene in process of his(its) increase or reduction, thereby, избавляясь from processes, negative influencing upon quality of the seal. For any scanner and any parameter of the adjustment quality and accuracy цветопередачи are changed depending on display or printer, used by you for viewing result scans. Exactly so so it is important to have simple in use the facility of the calibration. Remember that scenes, which well look on screen, unnecessary will in the same way well look at printout on printer, but qualitative scenes, got on printer, can look not so on screen well. If you want to execute the calibrations for screen and printer then at scan make sure that use the corresponding to calibre file. For this usually it is necessary to report the driver Twain, on what device you are going to to get the final scene.

The Level of the noise and close connected with him attitude signal-noise - a most most important factors that, insofar will well send the detail got at scan scene. At familiarization with низкокачественными scenes got when performing test, take into account that they are received with taken by default parameter of the adjustment scanner and you may vastly change the level a relations signal-noise, having changed parameters of the adjustment in driver Twain. For instance, scanners HP and Epson have shown the bad results for relations signal-noise. However taken by default parameters of the adjustment these scanner do the scene more light that enlarges the noises. The Reduction parameter to brightness will bring also to noise level reduction in scene.

The Joining (the information) colour - a factor that, insofar well three colours are situated comparatively each other - usually not so it is important for colour photography, but can turn out to be important at scan of the stroke graphic scenes. If joining colour is executed bad then on edge will be a mark additional colour halo. When printing on jet or lazer printer, or at scan for page Web offset colour even on whole pixel at permit of the scan 600 dpi usually acceptable though it will be observable at scan with permit 300 dpi.

Author: А. V. Savin It Is Added: 03.05.2007