Re: Standard set of image pre-processing filters for poorly hand printed images?

Milind Joshi <milind.a.joshi@xxxxxxxxx> wrote in
news:1194298697.468355.198420@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:

Hi,

Does anyone know of a standard filter or filters applied in sequence
to a B/W hand printed images to fill in broken lines, etc., without
affecting those characters that are well-written with complete
strokes?

We have a bunch of images with different writing styles, applying a
single set of filters on all of them deteriorates quality on those
images that were good.

Also, applying filters and checking results to see if the filter was
OK is too time-consuming.

Standard thickening/smoothing operations built into OCR/ICR engines
didn't work very well, so we're going to have to write a custom image
pre-processor for these images.

You can find a sample at
http://www.ideatechnosoft.com/sci.image.processing/2007_11_05_sci.image
.processing_sample_image.TIF

There are many more samples, so that should not be a problem if you
want us to try out suggestions on a wider set of images.

What would be a general approach to arrive at a good sequence of image
processing filters or to choose the best one for the job? Is there a
filter out there that is recommended for this type of problem?

Any help, pointers, reading material, manuals, expert suggestions
would be greatly appreciated!

Best Regards,
Milind




If the images are B/W, i.e. "binary" images, there are standard morphological operators that deal with
shape transformations. For example, to make objects more solid and compact, the "closure"
procedure is applied (dilation and erosion filters in sequence). If edges are to be enhanced before
thresholding, an edge enhancement operator is applied (e.g. Canny or Sobel).

There are many approaches to improve a binary image like the ones you have (pre-OCR processing)
but it depends on the exact situation and the properties of the scanning system (e.g. you might need
image denoising and equalization filters before anything else). Take a look at a standard textbook in
digital image processing, like Gonzalez's or similar, and experiment with morphological filters.



--
Harris
.

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