Forums › TWAIN Direct › Ability information for the TWAIN DIRECT scanner
How does the TWAIN DIRECT client know the capabilities of the TWAIN DIRECT scanner?
I could not find it in the TWAIN DIRECT specification.
The TWAIN Direct Specification discusses this, but here’s the answer in brief. Application are not expected (or more importantly required) to query a scanner for all of its possible settings. Instead a task is submitted to a scanner, which acts on it to the best of its abilities, which may include ignoring a setting it cannot perform. The application has the option to ask for multiple settings in decreasing priority within a single task. It may also require a specific setting, and if that setting cannot be satisfied the scanner must fail the task.
If absolutely necessary tasks can be used to probe for major accessories, such as bar code or printer support by attempting to turn them on with a fail exception, and examining the result. Note that if a fail exception is specified in a task, and the scanner reject it, it must provide information that precisely identifies the element that failed, so that applications can inform their users. This behavior is mandatory, and is confirmed through the self-certification tool.
I hope that helps clarify.
Thank you, markm
I was able to understand that the application does not need to know in advance the function of the scanner.
Your explanation was very nice and helpful.
Thank you very much.