In the printer market, de facto standards are established for the command sets used to control different types of printer - Epson's ESC/P for inkjet and dot matrix printers, Hewlett- Packard's PCL for laser printers, and Adobe's PostScript for high resolution laser printers and image-setters.
There is, however, no established standard for the actual commands (the 'escape codes') used to control scanners - each manufacturer uses their own command set. Until recently this restricted the number of software products which could be used with scanners. Software companies had to write separate drivers to handle each scanner make and model and their different interfacing requirements. They also had to update their products continually to support the latest models on the market. The workload this imposed often meant that a full range of drivers was not available until some time after the launch of a new scanner or software package.
{2}The solution came with the introduction of the TWAIN standard, developed jointly by Caere, Aldus, Hewlett- Packard, Logitech and Kodak - all leading companies involved with scanning software and hardware. TWAIN - which was not originally an acronym for anything although several appropriate ones have since been suggested - is a high-level programming standard for 'image acquisition devices' - typically scanners, but other devices come into the same category. In a TWAIN environment just one driver file, the 'Data Source', is needed for each device. This driver is usually written by the scanner manufacturer and performs several tasks.
It provides standard functions which software packages can use for making basic settings such as scanning resolution and scanning area selection.
It provides the 'control panel' which can be displayed to the user if the software package allows it, for manually setting up the various options available. (Most software will always display the control panel. However, a package scanning a whole page at a fixed resolution may choose to by-pass the control panel).
Finally, it reads the image data from the scanner and sends it back to the application in a standard format.
{3}TWAIN is a high-level software interface which ensures that software packages (and the programmers who write them) do not need to worry about individual scanner control commands or how they work.
The developer of a new application simply has to make it TWAIN-compatible, and it will then be able to work with existing scanners for which a Data Source driver is available. Similarly, a hardware manufacturer only needs to make one Data Source driver available for their scanners, which should then be able to work with most TWAIN-compatible software.
{4}At the time of writing, TWAIN standards have been defined for the Microsoft Windows environment (on PC-compatible machines) and the Apple Macintosh environment. It is likely that TWAIN standards will be developed for additional environments in the future.
