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<div class="moz-cite-prefix">On 11-Feb-18 14:29, Davis Johnson
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:692a1de4-95b6-c921-3f62-4a7670b0e775@frizzen.com">I
think what you need is a wide carriage printer with the typical
feed up through a slot in the bottom, and a camera.
<br>
<br>
The only working function needed from the printer is form feed.
Photograph the page that is hanging below the printer, form feed
and repeat.
<br>
<br>
Anybody here ought to be able to handle the programming to
automate this process.
<br>
<br>
You would need to manually photograph the first page.
<br>
<br>
The camera would need good depth of field.
<br>
<br>
<br>
</blockquote>
It's not that simple. You need to deal with at least 2 common
vertical pitches (6 & 8 LPI), and a number of page lengths (and
widths). These need to be setup per job; not all printers support
all these. Plus, misalignment (as Al noted, crossing the
perforations at the bottom of a page is quite common). The OP
mentioned that his listings have a hard crease; this will cause (at
least) feed and stacking problems. Form feed causes a high-speed
slew; this becomes less reliable as the distance moved increases.
You're proposing an entire page at a time - which means that the
paper will jump off the tractors frequently.[1] Old paper is
fragile. Over hundreds of pages, dimensions may not be stable; it
was not uncommon to have to re-adjust TOF after a while. There's a
fair bit of error detection and recovery to work out.<br>
<p>Lighting is an issue, as is compensating for keystoning and other
misalignments. Most cameras don't have a standard remote trigger
interface - one of the pointers I provided loads modified firmware
into cameras from one manufacturer to make this work. If you look
at digital camera reviews, you'll see that the lenses have varying
degrees of artifacts, especially at the edges. So you need to
find and zoom to an area that's relatively "flat" & doesn't
need a lot of correction. While depth of field will help, it also
will result in apparent font size changes as paper sways forward
and back. If you stop that, you simplify the OCR - and don't need
as much depth of field.<br>
</p>
<p>There are many backgrounds that need to be subtracted for OCR to
work. (Printer paper was notorious for institutional logos, as
well as bars and other aids to human readers.) Then there are the
other issues mentioned in my earlier note.<br>
</p>
<p>It seems simple, but it is a P.roject. That's a capital P. With
a lot of roject to work out.<br>
</p>
<p>It's worthwhile, but it's not simple. It's a pretty interesting
hardware (and software) project. I don't mean to discourage
anyone who wants to work on it - but you need to go in with eyes
open, or you'll end up very, very frustrated.<br>
</p>
<p>Thunderscan tried to scan line by line & retrieve grayscale;
the challenges were piecing together the adjacent lines with pixel
resolution. The focal distance was constant because the camera
was on a carriage. The idea here is to capture a page per frame.
So the registration problems are quite different. One could try
the thunderscan approach; it would trade one set of problems xxx
"challenges and opportunities" for another.<br>
</p>
[1] In my experience, with many brands and models of tractor feed
printers over many years. Paper handling is really difficult to get
right.<br>
<br>
<blockquote type="cite"
cite="mid:692a1de4-95b6-c921-3f62-4a7670b0e775@frizzen.com">On
02/11/2018 01:17 PM, Al Kossow wrote:
<br>
<blockquote type="cite">
<br>
On 2/11/18 10:11 AM, Dan Gahlinger wrote:
<br>
<br>
<blockquote type="cite">which is why I wondered what people
thought of turning an old DEC teletype or printer into a
scanner, by fixing a camera
<br>
to it
<br>
</blockquote>
sounds like a bigger version of the Thunderscan
<br>
<a class="moz-txt-link-freetext" href="https://www.folklore.org/StoryView.py?story=Thunderscan.txt">https://www.folklore.org/StoryView.py?story=Thunderscan.txt</a>
<br>
<br>
</blockquote>
</blockquote>
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