Applications Programming Interface

Drawing applications such as GIMP or Adobe Photoshop must communicate with the scanner.There are many different scanners, many of which use different protocols.To simplify application programming,a number of Application Programming Interfaces ("APIs") have been developed.The API provides a unified interface for scanners.This means that the application does not need to know the specific details of the scanner to access it directly.For example,Adobe Photoshop supports the TWAIN standard; therefore Photoshop can theoretically acquire images from any scanner that has a TWAIN driver.In practice,applications that communicate with scanners often have problems.There may be bugs in the implementation of the API by the application or by the scanner manufacturer (or both).

Typically,the API is implemented as a dynamic link library.Every scanner manufacturer provides software that translates API procedure calls into raw commands that are sent to a hardware controller (such as a SCSI,USB,or FireWire controller).The manufacturer's part of the API is often called a device driver,but that's not strictly an accurate name: the API doesn't run in kernel mode and doesn't access the device directly.Instead,the Scanner API library translates application requests into hardware requests.

Common scanning software API interface:

SANE (Scanner Access Now Easy) is a free/open source API for accessing scanners.Originally developed for Unix and Linux operating systems,it has been ported to OS/2, Mac OS X, and Microsoft Windows.Unlike TWAIN, SANE does not deal with the user interface. This allows batch scanning and transparent network access without any special support from device drivers.Most scanners use TWAIN.Originally intended for low-end and home appliances,it is now widely used for high-volume scanning.ISIS (Image and Scanner Interface Specification) was created by Pixel Translations,still uses SCSI-II for performance reasons,and is used by large departmental machines.WIA (Windows Image Acquisition) is an API provided by Microsoft for Microsoft Windows.

Bundled applications

Although any software other than a scanning utility is not a feature of any scanner,many scanners come bundled with software. Usually,some type of image editing application (such as Adobe Photoshop) and optical character recognition (OCR) software are provided in addition to the scanning utility.OCR software converts a graphic image of text into standard text that can be edited with common word processing and text editing software; accuracy is rarely perfect.

Output data

Some scanners, especially those designed for scanning printed documents,can only scan in black and white,but most modern scanners can scan in color.For the latter, the scan result is an uncompressed RGB image that can be transferred to the computer's memory.Color output will vary from scanner to scanner due to the spectral response of the sensing element,the nature of the light source, and corrections applied by the scanning software.While most image sensors have a linear response,the output values are often gamma compressed.Some scanners use embedded firmware to compress and clean up images.Once in the computer,the image can be manipulated with a raster graphics program such as Adobe Photoshop or GIMP and saved on a storage device such as a hard drive.Images are usually stored on a hard disk.Images are usually stored in image formats such as uncompressed Bitmap,"lossless" compressed TIFF and PNG, and "lossy" compressed JPEG.Documents are best stored in TIFF or PDF format;JPEG is not particularly suitable for text.Optical Character Recognition (OCR) software allows for the conversion of scanned images of text into editable text with reasonable accuracy,as long as the text is printed clearly, in a font and size that can be read by the software.OCR functionality can be integrated into the scanning software, or a separate OCR program can be used to process scanned image files.

Document camera scanners

Another type of document scanner is a document camera.Capturing images on a document camera differs from flatbed scanners and automatic document feeder (ADF) scanners because the scanned object requires no moving parts.Typically, an illuminated/reflective bar inside the scanner must move over the document (eg for flatbed scanners),or the document must pass through the bar (eg for feeder scanners) to produce the entire scanned image.Document cameras capture an entire document or object in one step, usually in an instant.Typically,the document is placed on a flat surface,usually a desk, below the capture area of the document camera.The process of capturing the entire surface at once facilitates increased reaction times for scanning workflows.Once the image is captured, it is usually processed through software that can enhance the image and perform tasks such as automatic rotation, cropping, and straightening.There is no need for the document or object being scanned to be in contact with the document camera,thus increasing flexibility in the types of documents that can be scanned.Objects that were previously difficult to scan on conventional scanners can now be done with a single device.This especially includes documents that vary in size and shape,are bound,are in folders, or are bent/crumpled,which can get jammed in the feed scanner.Other objects include books,magazines,receipts,letters,bills,etc.Having no moving parts also eliminates the need for maintenance,which is a consideration in the total cost of ownership, which includes the scanner's ongoing operating costs.Increasing latency while scanning is also beneficial in the area of contextual scanning.ADF scanners, while very fast and very good at batch scanning, also require pre- and post-processing of documents. Document cameras can be integrated directly into a workflow or process,such as a teller at a bank.Documents are scanned directly in the customer's context where the document will be placed or used.In these cases, reaction time is an advantage.Physical cameras also typically require little space and are often portable.While the response time for scanning with a document camera may be fast,an ADF scanner is more efficient for scanning large batches of uniform,unbound documents.Such techniques are challenged by external factors such as lighting that can affect scan results.The way these problems are solved depends a lot on the complexity of the product and how it handles them.