Editing Image scanner (section)

== Scan quality ==
Color scanners typically read RGB (red-green-blue) color data from the array. 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).

[[Color depth]] varies depending on the scanning array characteristics, but is usually at least 24 bits. High-quality models have 36-48 bits of color depth.

Another qualifying parameter for a scanner is its [[Image resolution|resolution]], measured in [[Pixel density|pixels per inch]] (ppi), sometimes more accurately referred to as [[samples per inch]] (spi). Instead of using the scanner's true optical resolution, the only meaningful parameter, manufacturers like to refer to the interpolated resolution, which is much higher thanks to software [[interpolation]]. {{As of|2009}}, a high-end flatbed scanner can scan up to 5400 ppi and drum scanners have an optical resolution of between 3000 and 24000 ppi.

''Effective resolution'' refers to the true resolution of a scanner, and is determined by using a resolution test chart. The effective resolution of most all consumer flatbed scanners is considerably lower than the manufactures' given optical resolution.<ref name="filmscanner.info">{{cite web | date=2007 | url=http://www.filmscanner.info/en/EpsonPerfectionV750Pro.html | title=Scanner test report: Epson Perfection V750 Pro | work=ScanDig | last=Wagner | first=Patrick | archiveurl=https://web.archive.org/web/20240407050047/https://www.filmscanner.info/en/EpsonPerfectionV750Pro.html | archivedate=April 7, 2024}}</ref>

Manufacturers often claim interpolated resolutions as high as 19200 ppi; but such numbers carry little meaningful value because the number of possible [[digital zoom|interpolated pixels]] is unlimited, and doing so does not increase the level of captured detail.

The size of the file created increases with the square of the resolution; doubling the resolution quadruples the [[file size]]. A resolution must be chosen that is within the capabilities of the equipment, preserves sufficient detail, and does not produce a file of excessive size. The file size can be reduced for a given resolution by using "lossy" compression methods such as JPEG, at some cost in quality. If the best possible quality is required lossless compression should be used; reduced-quality files of smaller size can be produced from such an image when required (e.g., image designed to be printed on a full page, and a much smaller file to be displayed as part of a fast-loading web page).

Purity can be diminished by scanner noise, optical flare, poor analog to digital conversion, scratches, dust, [[Newton's rings]], out-of-focus sensors, improper scanner operation, and poor software. Drum scanners are said to produce the purest digital representations of the film, followed by high-end film scanners that use the larger Kodak Tri-Linear sensors.

The third important parameter for a scanner is its [[dynamic range]] (also known as density range). A high-density range means that the scanner is able to record shadow details and brightness details in one scan. Density of film is measured on a base 10 log scale and varies between 0.0 (transparent) and 5.0, about 16 stops.<ref name="ReferenceA">{{cite web | url=http://www.filmscanner.info/en/Dichte.html | title=Density and density range of scanners | work=ScanDig | last=Wagner | first=Patrick | date=n.d. | archiveurl=https://web.archive.org/web/20240413044016/https://www.filmscanner.info/en/Dichte.html | archivedate=April 13, 2024}}</ref> Density range is the space taken up in the 0 to 5 scale, and Dmin and Dmax denote where the least dense and most dense measurements on a negative or positive film. The density range of negative film is up to 3.6d,<ref name="ReferenceA"/> while slide film dynamic range is 2.4d.<ref name="ReferenceA"/> Color negative density range after processing is 2.0d thanks to the compression of the 12 stops into a small density range. Dmax will be the densest on slide film for shadows, and densest on negative film for highlights. Some slide films can have a Dmax close to 4.0d with proper exposure, and so can black-and-white negative film.

Consumer-level flatbed photo scanners have a dynamic range in the 2.0–3.0 range, which can be inadequate for scanning all types of [[photographic film]], as Dmax can be and often is between 3.0d and 4.0d with traditional black-and-white film. Color film compresses its 12 stops of a possible 16 stops (film latitude) into just 2.0d of space via the process of dye coupling and removal of all silver from the emulsion. Kodak Vision 3 has 18 stops. So, color-negative film scans the easiest of all film types on the widest range of scanners. Because traditional black-and-white film retains the image creating silver after processing, density range can be almost twice that of color film. This makes scanning traditional black-and-white film more difficult and requires a scanner with at least a 3.6d dynamic range, but also a Dmax between 4.0d to 5.0d. High-end (photo lab) flatbed scanners can reach a dynamic range of 3.7, and Dmax around 4.0d. Dedicated film scanners <ref>{{cite web | url=https://www.filmscanner.info/en/FilmscannerRangliste.html | title=Film scanner ranking and scanner comparison | last=Wagner | first=Patrick | date=n.d. | archiveurl=https://web.archive.org/web/20240525213133/https://www.filmscanner.info/en/FilmscannerRangliste.html | archivedate=May 25, 2024}}</ref> have a dynamic range between 3.0d–4.0d.<ref name="ReferenceA"/> Office document scanners can have a dynamic range of less than 2.0d.<ref name="ReferenceA"/> Drum scanners have a dynamic range of 3.6–4.5.

For scanning film, {{visible anchor|infrared cleaning|text=[[infrared cleaning]]}} is a technique used to remove the effects of dust and scratches on images scanned from film; many modern scanners incorporate this feature. It works by scanning the film with infrared light; the dyes in typical color film emulsions are transparent to infrared light, but dust and scratches are not, and block infrared; scanner software can use the visible and infrared information to detect scratches and process the image to greatly reduce their visibility, considering their position, size, shape, and surroundings. Scanner manufacturers usually have their own names attached to this technique. For example, [[Seiko Epson|Epson]], [[Minolta]], [[Nikon]], [[Konica Minolta]], [[Microtek]], and others use [[Digital ICE]], while [[Canon Inc.|Canon]] uses its own system, [[Film Automatic Retouching and Enhancement|FARE]] (Film Automatic Retouching and Enhancement).<ref>{{cite web | url=http://www.canon.com/technology/canon_tech/explanation/fare.html | publisher=Canon Inc. | access-date=May 2, 2007 | title=Film Automatic Retouching and Enhancement | url-status=dead | archive-url=https://web.archive.org/web/20101023211251/http://www.canon.com/technology/canon_tech/explanation/fare.html | archive-date=October 23, 2010}}</ref> [[Plustek]] uses [[LaserSoft Imaging]] [[iSRD]]. Some independent software developers design infrared cleaning tools.

By combining full-color imagery with 3D models, modern hand-held scanners are able to completely reproduce objects electronically. The addition of 3D color printers enables accurate miniaturization of these objects, with applications across many industries and professions.

For scanner apps, the scan quality is highly dependent on the quality of the phone camera and on the framing chosen by the user of the app.<ref>{{Cite web | url=http://help.thegrizzlylabs.com/article/94-what-is-the-resolution-in-dpi-of-the-scans | title=What is the DPI of my scans? | work=The Grizzly Labs | access-date=December 8, 2017 | archiveurl=https://web.archive.org/web/20240530140134/http://help.thegrizzlylabs.com/article/94-what-is-the-resolution-in-dpi-of-the-scans | archivedate=May 30, 2024}}</ref>