how to tell if image is from front or back of page

[spike]

Suppose I’m scanning a document in duplex mode, with the scanner configured to discard blank pages: When it scans a page that has text on the front but is blank on the back, the scanner sends the front of that page, then discards the back and sends the front of the *next page*. Can any of you TWAIN gurus propose a way to detect that this has happened? We don’t want to discard blank backs, just pages that are blank on both sides. If there is no way to detect the situation, it makes it impossible to use the scanner’s blank-page-discard feature during duplex scanning – we’ll have to go to software blank-page detection.

I’ve found the extended info called TWEI_CAMERA – has anybody ever used or implemented this? I’m assuming Mark M. has…

[gabe]

what device are you working with? I’ve got an i65 that i can test twei_camera with. is this problem specific to one device or do you need to be able to check this for multiple models?

but I’d guess (until i verify this) that you’re looking at the right thing, that TWEI_CAMERA is your trick. if you’re pulling extinfo after every scan, then you should see an alternating camera. top then bottom then top then bottom…. and if you see top top or bottom bottom then you’ve got your issue.
but my question here – then what? and why?
I dont understand when/where this would matter. But I’d like to be able to recognize when I should worry about this.

[spike]

Hi Gabe – sorry, missing background: My customer is using a Canon (I expect a DR-series) that has an onboard blank-page-discard. So when he runs it in duplex with blank-page-discard, it tosses out the blank backs of pages. Evidently this is not what customer wants… he wants to discard pages whose sides are both blank, and so we got wondering if there was a TWAIN way to do this, instead of just handling the blank-page-discard in software.

I think the concept is that if the application sees , – it knows a blank back was tossed, and has the option of reinserting the missing blank image in the output stream. (And if we see , , we know a page was scanned that had a blank front and information on the back…)

Anyway – that’s what got me into this. I guess I’ll add some extinfo support to EZTwain and my other tools, and see if the Canon DR-series makes anything useful available.

[gabe]

On further investigation it seems to me than TWEI_CAMERA doesn’t really exist. I see it on page 64 of ther spec, but when I check the toolkit sample, there is no such thing. In fact the only mention of camera is from filesystem.

Spike, are you able to get Camera info from ExtImageInfo? what did you use for the InfoID?

[gabe]

pay no attention to the guy with the old twain header.
yeah, i found it.

[j_t]

I have the same issue as Spike, with a Fujitsu fi-4750C that supports Blank Page Detection, but does not support extImageInfo (DAT_EXTIMAGEINFO).

I have always used the TWEI_PAGENUMBER or TWEI_CAMERA to handle blank pages in the past.

Any Ideas?

[Author]

Posts