OT: scanning

[Brian K. White]

On 10/29/2010 9:35 AM, Fairlight wrote:
> On Fri, Oct 29, 2010 at 06:06:38AM -0700, after drawing runes in goat's blood,
> Bob Rasmussen cast forth these immortal, mystical words:
>> The Windows module (twain32.dll) is a common interface to the Twain
>> drivers supplied by the various scanners. Talking to twain32.dll is like
>> talking to the GDI to do printing. There are still a zillion details to
>> deal with.
>
> He's dealing with C code...should be par for the course.  :)

I was gonna say just what Bob said.
It's very much not simple to use twain directly and I'm not even 
slightly remotely anywhere near able to even think about it.

That's why there are almost no free twain implementations, and none of 
them even remotely feature rich, but there are dozens of commercial 
libraries that cost hundreds to thousands of dollars. Anyone trying to 
do twain discovers the same thing and buys a library like dtwain. In 
fact even dtwain is a bit beyond me. I use twainsave, which uses dtwain 
internally.

The library I currently use does a loooot of work to present me with a 
single function call. When debugging an "El Cheapacabbra" HP all-in-one 
recently, running the lib with it's debug log enabled, you wouldn't 
believe the conversation that goes on back & forth to set up and the 
perform a scan.
Something like 750k of text of twain commands going back & forth, and 
that's just the failed scan, no image data transfer.

And even more joy, Bob said some discovery has to go on. Right, it 
should be obvious, not all scanners or their drivers support all 
features defined in the standard right? So the standard includes 
commands so that an application can ask a scanner driver "do you support 
capability X?" etc, and then gracefully operate the scanner by only 
using functions it supports. Makes sense right? A well written app will 
use those commands to avoid problems.

Problem is, merely asking the scanner some of these questions choked the 
scanner! How can you win when the very act of performing due diligence 
itself breaks the thing?

-- 
bkw