[Openimaj-discuss] Stroke Width Transformation for text detection

[Charlie P. <x.p...@fr...>]

Dear Team,

First of all thanks for sharing this java library (with the great
tutorials and documentation) with which I'm discovering the world of
computer vision! Indeed I'd like to see if there are any noticeable
performance (and accuracy) improvements by applying text detection
before OCR (the corpus I am using is made of scanned images).

To practice I am using http://i.stack.imgur.com/EingC.jpg and I like to
apply the Stroke Width Transform algorithm on it but first the image I
get now after applying SWT is all white (can't find the right parameter
values, although it had worked just beforehand), and then I am lost on
how to get the text regions.

Here is the code I used (inspired from
https://sourceforge.net/p/openimaj/discussion/general/thread/a56f1a03/) :

Main():
/                URL u = new URL("http://i.stack.imgur.com/EingC.jpg");//
//                FImage grayImage = ImageUtilities.readF( u
).normalise().process( new ResizeProcessor( 620 ) );//
//                DisplayUtilities.display(grayImage);//
//                applySWTOnImage(grayImage);/

applySWTOnImage():/

                private void applySWTOnImage (FImage input){
                float threshCannyLow = (float)0.1;
                StrokeWidthTransform swt = new
StrokeWidthTransform(true, threshCannyLow, Math.min(threshCannyLow * 3,
1),  (float)0.9); 
                swt.processImage(input);
                DisplayUtilities.display(input);
            }
/
Regarding the parameters, somewhere in OpenCV documentation was written
that the higher threshold in Canny was recommended to be 3 times the
lower (can't find it anymore) that's why I set them as such in the
constructor.

As it worked and does not anymore, I could see the result of SWT
algorithm a limited number of time, but I am stuck on what to do then to
get the text boundaries as shown in the SWT paper
(http://yoni.wexlers.org/papers/2010TextDetection.pdf) or everywhere
when people show their results with SWT.

So my questions are : why has the result of applying SWT become all
white, or as it may be hard to answer, how should the SWT parameters be
chosen to get something, and could you give me some hints on the steps
to follow after the SWT ?

Thanks a lot for helping and keep up this great work!

Regards,

CP