Editing Image scanner (section)

== Connectivity{{anchor|Computer connection}} ==
[[File:Photoshop goddess version 1.05 (3378276180).jpg|thumb|A [[photographic print]] being scanned into a computer at the photo desk of the ''[[The Detroit News|Detroit News]]'' in the early 1990s]]
Scans must virtually always be transferred from the scanner to a computer or information storage system for further processing or storage. There are two basic issues: (1) how the scanner is physically connected to the computer and (2) how the application retrieves the information from the scanner.

=== Direct connection {{anchor|Direct physical connection to a computer}} ===
The file size of a scan can go up to about 100&nbsp;MB for a 600&nbsp;dpi, 23&nbsp;× 28&nbsp;cm (slightly larger than [[ISO 216|A4 paper]]) uncompressed [[24-bit color|24-bit]] image. Scanned files must be transferred and stored. Scanners can generate this volume of data in a matter of seconds, making a fast connection desirable.

Scanners communicate to their host computer using one of the following physical interfaces, listing roughly from slow to fast:
* [[Parallel port]]&nbsp;– Connecting through a parallel port is the slowest common transfer method. Early scanners had parallel port connections that could not transfer data faster than 70 [[kilobyte]]s/[[second]]. The primary advantage of the parallel port connection was economic and user skill level: it avoided adding an interface card to the computer.
* [[GPIB]]&nbsp;– General Purpose Interface Bus. Certain drum scanners like the Howtek D4000 featured both a SCSI and GPIB interface. The latter conforms to the IEEE-488 standard, introduced in the mid-1970s. The GPIB interface has only been used by a few scanner manufacturers, mostly serving the DOS/Windows environment. For Apple Macintosh systems, National Instruments provided a [[NuBus]] GPIB interface card.
* [[SCSI|Small Computer System Interface (SCSI)]]&nbsp;– SCSI is rarely used since the early 21st century, supported only by computers with a SCSI interface, either on a card or built-in. During the evolution of the SCSI standard, speeds increased. Widely available and easily set up USB and Firewire largely supplanted SCSI.
* [[USB|Universal Serial Bus (USB)]]&nbsp;– USB scanners can transfer data quickly. The early USB 1.1 standard could transfer data at 1.5 megabytes per second (slower than SCSI), but the later USB 2.0/3.0 standards can transfer at more than 20/60 megabytes per second in practice.
* [[IEEE 1394|FireWire]]&nbsp;– Also known as IEEE-1394, FireWire is an interface of comparable speed to USB 2.0. Possible FireWire speeds are 25, 50, and 100, 400, and 800 megabits per second, but devices may not support all speeds.
* [[Proprietary hardware|Proprietary]] interfaces&nbsp;– Bespoke interfaces were used on some early scanners that used a proprietary interface card rather than a standard interface.<!--Mustek?-->

=== Indirect connection {{anchor|Indirect (network) connection to a computer}} ===
During the early 1990s professional flatbed scanners were available over a [[Local area network|local computer network]]. This proved useful to publishers, print shops, etc. This functionality largely fell out of use as the cost of flatbed scanners reduced enough to make sharing unnecessary.

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.

Battery-powered portable scanners store scans on internal memory; they can later be transferred to a computer either by direct connection, typically USB, or in some cases a [[memory card]] may be removed from the scanner and plugged into the computer.

=== Applications programming interface {{anchor|Applications Programming Interface}} ===
A raster image editor must be able to communicate with a scanner. There are many different scanners, and many of those scanners use different protocols. In order to simplify applications programming, some [[application programming interface]]s (APIs) were developed. The API presents a uniform interface to the scanner. This means that the application does not need to know the specific details of the scanner in order to access it directly. For example, [[Adobe Photoshop]] supports the [[TWAIN]] standard; therefore in theory Photoshop can acquire an image from any scanner that has a TWAIN driver.<!--GIMP + SANE?-->

In practice, there are often problems with an application communicating with a scanner. Either the application or the scanner manufacturer (or both) may have faults in their implementation of the API.

Typically, the API is implemented as a [[Library (computing)|dynamically linked library]]. Each scanner manufacturer provides software that translates the API procedure calls into primitive commands that are issued to a hardware controller (such as the SCSI, USB, or FireWire controller). The manufacturer's part of the API is commonly called a [[device driver]], but that designation is not strictly accurate: the API does not run in kernel mode and does not directly access the device. Rather the scanner API library translates application requests into hardware requests.

Common scanner software API include:

* [[TWAIN]]&nbsp;– An API used by most scanners. Originally used for low-end and home-use equipment, it is now widely used for large-volume scanning.
* [[Scanner Access Now Easy|SANE (Scanner Access Now Easy)]]&nbsp;– A [[Free software|free]]/[[Open-source model|open-source]] API for accessing scanners. Originally developed for [[Unix]] and [[Linux]] operating systems, it has been ported to [[OS/2]], [[macOS|Mac OS X]], and [[Microsoft Windows]]. Unlike TWAIN, SANE does not handle the user interface. This allows batch scans and transparent network access without any special support from the device driver.
* [[Windows Image Acquisition|Windows Image Acquisition (WIA)]]&nbsp;– An API provided by Microsoft for use on [[Microsoft Windows]].
* [[Image and Scanner Interface Specification|Image and Scanner Interface Specification (ISIS)]]&nbsp;– Created by Pixel Translations, which still uses [[SCSI-2]] for performance reasons, ISIS is used by large, departmental-scale, machines.

=== Bundled applications ===
Although no software beyond a scanning utility is a feature of any scanner, many scanners come bundled with software. 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. OCR software converts graphical images of text into standard text that can be edited using common word-processing and text-editing software; accuracy is rarely perfect.