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Re: [vox-tech] OCR notes
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Re: [vox-tech] OCR notes



På 2007-04-11, skrev Dylan Beaudette:
> Hi everyone,
> 
> I am about to embark on an exciting adventure into the land of original 
> character recognition, processing nearly 1,000 documents and extracting 
> numbers from them. I am interested in any anecdotal wisdom regarding:
> 
> 1. efficient scanning parameters:
> DPI
> color / BW / grayscale

B&W, as high DPI as feasible.

> 2. pre-processing steps one might do with imagemagick

Clipping off borders is recommended.

> 3. any filtering that one might do to get ready for the OCR

Make sure there are no handwritten notes, post-it pieces, or other
miscellaneous cruft on the documents before scanning them. If the paper
is colored or there are ghost images (such as the back-side printing
showing through thin paper), scan in grayscale and then carefully reduce
to B&W with an appropriate hand-picked threshhold. I think I used
pnmremap to do that the last time that need came up for me.

> I plan to use Google's new OCR project, ocropus, which currently uses 
> the 'tesseract' engine. Naive attempts to OCR these documents is resulting in 
> marginal accuracy, so any help is appreciated. Vertical and horizontal lines 
> on the original documents are confusing the OCR, so removing them might be a 
> start. I have thought about extracting each 'cell' of data with imagemagick, 
> and then running the resulting mini-images though the OCR... that might be a 
> last resort though...

Neat. I've never tried that. The only OCR engine I've sucessfully used
is gocr, which was pretty decent and worked out of the box with minimal
tweaking. I tried Clara but it seemed unstable and I gave up before I
could figure out how to make it work.


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