TWAIN driver
Surprisingly TWAIN is not an acronym, but a very important standard in image acquisition, developed by Hewlett-Packard, Kodak, Aldus, Logitech and Caere which specifies how image acquisition devices such as scanners, digital cameras and other devices transfer data to software applications. TWAIN allows software applications to work with image acquisition devices without knowing anything about the device itself. If a device is TWAIN compliant and a software application is TWAIN compliant, the two should work together regardless of whether or not the software was bundled with the image acquisition device when it was purchased.
It is possible to attach more than one TWAIN compliant image acquisition device to a PC at the same time as shown in the diagram. Each of the devices will have its own separate TWAIN module. This makes it necessary for TWAIN compliant software applications to provide a means for the end user to select which TWAIN device to use during a session. In practice the "acquire" option in the File menu of an application such as PhotoShop would be selected. The user would be prompted to select a suitable TWAIN source which would launch the device's own driver, all without leaving the main application. After scanning, the driver automatically closes, leaving the scanned image open in the main application. No unnecessary quitting, launching, or saving of potentially large and possibly useless files.
Increasingly, manufacturers are shipping scanners with two TWAIN drivers. The first will be a basic, simplistic driver, aimed at the novice scanner. With this, scanning is basically a one-button affair. Click the preview button, and a small preview of the image appears on-screen, in a preview pane. From here, the scanning area may be adjusted along with the resolution and pixel depth. When completely happy with the preview results the Scan button is clicked to initiate the actual scan.
For more advanced there should be an Advanced Scanning Options button somewhere on the first driver. This will open the second driver, the one offering a higher degree of overall image adjustment such as brightness, contrast, colour and Gamma Correction. This allows adjustments to be made to specific ranges of tonal values, either as a whole, or to each primary colour in turn.
Colour calibration
One of the frustrations of using a desktop scanner is that a scanned image can look different on screen than it does when printed, and both can vary quite a bit from the original. The solution to this problem is a colour calibration (or colour matching) system. Such software is really valuable only for scans of high-quality images (transparencies, professional-quality prints, etc.) that need to meet rigorous quality standards - for most people using a desktop scanner, accurate colour is not as important as fast, pleasing colour. This is just as well, as the complexities of colour and human perception have made calibration a daunting challenge - and as a consequence, there are several different solutions already available, with more on the way.
One of the most comprehensive systems is the Kodak Colour Management System (CMS), which uses its own colour definitions together with profiles for each different scanner, monitor, and printer in the system to translate and standardise colours. Elements of the Kodak system are bundled with Adobe PhotoShop and other software, and CMS is rapidly becoming the favourite of graphic artists and others who depend on closely matched colours.
Other systems have been developed by individual scanner manufacturers and software publishers. These proprietary profile-based systems can also do the job, provided that they include profiles for all of the different devices that will be used for scanning, viewing, editing, and outputting the final image.
A final approach is known as output-based correction, and involves scanning and outputting a standard calibration target, and then making adjustments to colour profiles in order to standardise colours. This is a less sophisticated process, and is probably inappropriate for users who want to continually re-calibrate their systems for optimum results. For basic colour scanning, however, output-based correction is often sufficient.
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