Personally I think adjusting contrast settings does not help much. It needs special algorithm to get a good black-white image. In the literature, it is related to document binarization. You could google search to get some papers to look at.
On Saturday, January 12, 2013 9:16:45 AM UTC-6, Tin Siladin wrote: > > Thanks for your response. In the meantime, I read up on many of your > answers in this group which will be very valuable to me. Thank you for > sharing your expertise. > > I have in my incoming bitmap a single line of text (mostly numbers), so I > don't need to worry about most of the details you do. I believe the > variances in accuracy occur due to different lighting/brightness conditions > under which the picture is taken so sometimes the incoming grayscale image > is overall darker, etc. I've played around with contrast settings of the > camera, and that helps as well, but am still trying to improve. > Preprocessing to black and white was just one idea I had in mind. Needless > to say, I'm fairly new to tesseract, so read up on possibilities of setting > configuration parameters/variables which may help me. > > If you guys have nothing better to do, the "Show Processed Image" option > would be nice to have in Android as well. :) > > Thanks again, > Tin > > > On Saturday, 12 January 2013 15:47:27 UTC+1, Patrick Questembert wrote: >> >> Yes, we convert the image to black and white, that's the end result of >> any image processing for the purpose of OCR - Tesseract recognition has to >> work on a black & white image so either your app creates the b&w image or >> you let Tesseract create it. We had to create the b&w image because we >> found Tesseract's image processing to be inadequate for most business card >> images. Hard to fully describe all the details of our image processing but >> it include stages like detecting areas where patterns are present (as >> opposed to background), local adaptive thresholding and non-text >> elimination (the later is something we don't do too well yet - but >> Tesseract is usually not too confused by non-text patterns in the b&w >> image). You can see the b&w image we generate by turning ON a setting of >> ScanBizCards called "Show Processed Image" (available only in our iOS >> version, not the Android version). >> >> Note also that in the results you see in ScanBizCards it's not just about >> the b&w image: we also have 70,000 lines of code examining the text results >> returned by Tesseract and comparing to our home-brewed OCR tests then >> picking one or the other for each letter. >> >> Patrick >> >> On Sat, Jan 12, 2013 at 9:02 AM, Tin Siladin <[email protected]> wrote: >> >>> Patrick, >>> I ran into your answer and I think you might be able to help me given >>> that your scanbizcards app is doing similar processing to what I need >>> (don't worry, no competition :) ). >>> >>> I'm using tesseract-ocr on android, taking pictures of portions of >>> receipts in grayscale mode (EFFECT_MONO, if available on device), and >>> converting the bitmap to ARGB_888 for tesseract processing. I'm getting >>> pretty good results, but am trying to improve accuracy. >>> >>> Do you know whether you do any other preprocessing of the bitmap before >>> passing to tesseract, like perhaps converting to black/white (you mentioned >>> in your above answer you're passing "black & white image"). I tried out >>> your app and it seems to give better results than mine on similar types of >>> images. Very nice app, BTW. >>> >>> Thanks, >>> Tin >>> >>> On Monday, 17 December 2012 04:02:34 UTC+1, Patrick Questembert wrote: >>>> >>>> I think you are right - ScanBizCards is passing a black & white image >>>> to Tesseract and we are pretty sure Tesseract doesn't change the image >>>> (empirically - we never dug in to make sure). >>>> >>>> Patrick >>>> >>>> On Sun, Dec 16, 2012 at 9:44 PM, Linda Li <[email protected]>wrote: >>>> >>>>> If I pass a binary (black-white) image into tesseract-ocr, will >>>>> tesseract process the image on its own way? >>>>> >>>>> >>>>> It seems tesseract ocr uses Otsu global thresholding method (not >>>>> looking into the code carefull yet, but saw the key word “otsu” in the >>>>> source code) >>>>> >>>>> If so, the Otsu method will not change the binary (black-white) image. >>>>> >>>>> >>>>> So in my understanding, tesseract-ocr will not change the input >>>>> binary image. >>>>> >>>>> Just ask to make sure... >>>>> >>>>> >>>>> Thanks. >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "tesseract-ocr" group. >>>>> To post to this group, send email to [email protected] >>>>> To unsubscribe from this group, send email to >>>>> tesseract-oc...@**googlegroups.com >>>>> For more options, visit this group at >>>>> http://groups.google.com/**group/tesseract-ocr?hl=en<http://groups.google.com/group/tesseract-ocr?hl=en> >>>>> >>>> >>>> >>>> >>>> -- >>>> Patrick Questembert, *ScanBizCards* >>>> +1-917-250-4177 | www.scanbizcards.com >>>> twitter.com/ScanBizCards | >>>> www**.facebook.com/ScanBizCards<http://www.facebook.com/ScanBizCards> >>>> Just released: Power Contacts - http://itunes.apple.com/us/** >>>> app/power-contacts/**id476986356?mt=8<http://itunes.apple.com/us/app/power-contacts/id476986356?mt=8> >>>> >>>> -- >>> You received this message because you are subscribed to the Google >>> Groups "tesseract-ocr" group. >>> To post to this group, send email to [email protected] >>> To unsubscribe from this group, send email to >>> [email protected] >>> For more options, visit this group at >>> http://groups.google.com/group/tesseract-ocr?hl=en >>> >> >> >> >> -- >> Patrick Questembert, *ScanBizCards* >> +1-917-250-4177 | www.scanbizcards.com >> twitter.com/ScanBizCards | www.facebook.com/ScanBizCards >> Just released: Power Contacts - >> http://itunes.apple.com/us/app/power-contacts/id476986356?mt=8 >> > -- You received this message because you are subscribed to the Google Groups "tesseract-ocr" group. 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