Restoring Old Paper Tape
jrr at flippers.com
Fri Jan 22 00:48:43 CST 2016
On 01/21/2016 6:46 PM, Charles Anthony wrote:
> On Thu, Jan 21, 2016 at 6:21 PM, Jason T <silent700 at gmail.com> wrote:
>> On Thu, Jan 21, 2016 at 8:04 PM, Charles Anthony
>> <charles.unix.pro at gmail.com> wrote:
>>> For part 2, personally, I would take movies of the paper tape moving and
>>> doing image analysis to recover that data; this occurs to me because I've
>>> done a fair bit of image recognition software, so this solution may not
>>> feasible for all. If you sent me a sample movie, I would make a stab at
>>> writing some data recovery software.
>> I have heard of those approach and was thinking it may be a solution
>> in cases where the tape is too fragile (and that's pretty likely
>> here.) It would be well beyond my abilities but might make an
>> interesting project for you or anyone else with the skills.
> The general approach would be to have the tape backlit (on a piece of
> glass, with a light source and and diffuser underneath ) and guide block
> that the tape slides against so the holes move left-to-right but not up and
> down. The camera is set up so that the tape fills the image as much as is
> feasible. You start the camera, and slide the tape. Constant speed is not
> important, but avoid backing up.
> Grab a frame from the movie. Figure out the approximate pixel coordinates
> of the data and pin feed holes in the axis moving across the tape (eg, the
> 1 bit is about 24 pixels from the top of the image, the 2 bit is about 47
> pixels from the top, etc).
> Process the movie a frame at a time. Grab a column of pixels from the
> center of the image from top to bottom. Look at the pixels around where the
> pin feed is, decide if they are light or dark. If light, the a character is
> centered in the column. If not, move to the next frame. look at the pixels
> around where each data bit is, and decide if the are light (punched) or
> dark (unpunched). Write out that data. Skip frames until the pin feed
> pixels go dark, and then skip frames until it goes light again; that will
> be the next character. Repeat.
> The pin feed holes greatly simplify the process. This process is quite
> analogous to reading multi-track magnetic media with a timing track.
> Test on a known tape. Debug. Run over damaged tapes; data recovered.
> -- Charles
Would it not be simpler to make an optical reader to handle this job?
You need a light source and the correct number of opto transistors to
read the light from each hole. There is an index built into the tape so
that is easy to set.
Something like this:
Of course my assumption above is based on tape that is still complete.
If it has holes or can't be pulled then, yes, photographing and visually
reading the dot patterns may be necessary, but that sounds rather
impractical if there are more than a couple of tapes to transcribe.
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