ocr on subtitles

[franck dev]

Hi, I have tried to do ocr on subtitles picture but depending on the color of subtitle font it works or not
When the subtitle characters are in green it doesn't work
Could you give me some advices on parameters for tesseract I should use or how i should transform the picture before calling tesseract ?

Thanks,
Franck

[Dmitri Silaev]

Hi Franck,

It seems the problem here is not character color itself but rather char outlines and image transparency.

To get rid of all of these problems at once try converting your images to monochrome (use same old ImageMagick), like this - see the attachment. Tess then produces perfect results. If your other subtitle images have similar structure this method should work regardless of char color.

Best regards,
Dmitri Silaev
www.CustomOCR.com

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[Sriranga(82yrsold)]

tested in vietocr3.6 works fine. attached png and also output.txt.

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[franck dev]

Hi,

I tried with imagemagick:
-colorspace Gray
-negate

But tesseract doesn't work after this conversion
Which command have you used with imagemagic ?

With your picture the ocr works perfetcly
Thanks

[Sriranga(81+yrsold)]

I used IrfanView software to convert to grey scale.

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[Dmitri Silaev]

I used FastStone.

For ImageMagick use this:

- Source

(inet010.png)

- Get rid of transparency
>convert inet010.png -background black -alpha remove inet010_ntransp.png

(inet010_ntransp.png)

- Threshold
>convert inet010_ntransp.png -threshold 40% inet010_ntransp_ts.png

(inet010_ntransp_ts.png)

- Run Tess - perfect
>tesseract.exe inet010_ntransp_ts.png inet010_ntransp_ts.png
(inet010_ntransp_ts.png.txt)

Best regards,
Dmitri Silaev
www.CustomOCR.com

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