[jira] [Created] (TIKA-3361) Improve intelligence of OCRStrategy=AUTO

["Peter Kronenberg (Jira)" <ji...@apache.org>]

Peter Kronenberg created TIKA-3361:
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             Summary:  Improve intelligence of OCRStrategy=AUTO
                 Key: TIKA-3361
                 URL: https://issues.apache.org/jira/browse/TIKA-3361
             Project: Tika
          Issue Type: Improvement
            Reporter: Peter Kronenberg


Didn’t get a whole lot of feedback on the mailing list, so here’s my attempt at improving OCRStrategy=Auto

Currently, this strategy performs the following test
{code:java}
if (totalCharsPerPage < 10 || unmappedUnicodeCharsPerPage > 10) {
                    doOCROnCurrentPage(AUTO);
                }
{code}
I added a way to change the new numbers involved: the threshold for the total characters per page (below which, we OCR the page), and the threshold for unmapped characters (above which we OCR the page)

My main concern is with the unmapped characters. OCR adds a lot of overhead, which might not be necessary for simply a few unmapped characters

I added a new config, *OCRStrategyAuto*, which is only used if OCRStrategy=AUTO. Its format is
{code:java}
ocrStrategyAuto = best|fast|m[%], n
{code}
‘best’ and ‘fast’ are shortcuts. More later

m, n – m is the threshold for the number of unmapped characters per page. It can also be specified as a percentage. So, m=20 means if your page has more than 20 unmapped characters, it will OCR. m=20% means if the unmapped characters are more than 20% of the total characters, then it will OCR.

n is the threshold for the total number of characters on the page. n does not need to be specified and defaults to 10
{code:java}
<param name="ocrStrategyAuto" type="string">20</param>
{code}
is equivalent to
{code:java}
<param name="ocrStrategyAuto" type="string">20, 10</param>
{code}
*best* is shorthand for *20,10*
{code:java}
<param name="ocrStrategyAuto" type="string">best</param>
{code}
is equivalent to
{code:java}
<param name="ocrStrategyAuto" type="string">20, 10</param>
{code}
*best* is the default and is equivalent to the current behavior


 *fast* is a shortcut for *10%, 10*, which will avoid OCR unless the number of unmapped characters is greater than 10%
{code:java}
<param name="ocrStrategyAuto" type="string">fast</param>
{code}
is equivalent to
{code:java}
<param name="ocrStrategyAuto" type="string">10%, 10</param>
{code}



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