Improve quality of tesseract ocr result

Question

I'm developing an OCR app for Android using JNI and a code developed under C++ using OpenCV and Tesseract. It will be used to read a badge with an alphanumeric ID from a photo taken by the app.

I developed an code which handle with the preprocess of the image, in order to obtain a "readable image" as the one below:

I wrote the following function for "reading" the image using tesseract:

char* read_text(Mat input_image)
{
    tesseract::TessBaseAPI text_recognizer;
    text_recognizer.Init("/usr/share/tesseract-ocr/tessdata", "eng", tesseract::OEM_TESSERACT_ONLY);
    text_recognizer.SetVariable("tessedit_char_whitelist", "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789");
    text_recognizer.SetImage((uchar*)input_image.data, input_image.cols, input_image.rows, input_image.channels(), input_image.step1());
    text_recognizer.Recognize(NULL);
    return text_recognizer.GetUTF8Text();
}

The expected result is "KQ 978 A3705", but what I get is "KO 978 H375".

I did all the recommendations for improving the quality of the image from https://github.com/tesseract-ocr/tesseract/wiki/ImproveQuality. In addition, reading the docs from https://github.com/tesseract-ocr/docs, I tryed using an approximation of the images using polygons in order to get "better" features. The image I used is one like this:

With this image, I get "KO 978 A3705". The result is clearly better than the previous one, but is not fine.

I think that the processed image I pass to tesseract is fine enought to get a good result and I don't get it. I don't know what else to do, so I ask you for ideas in order to solve this problem. I need an exact result and I think I could get it with the processed image I get. Ideas please! =)

Have you tried different font sizes and resolutions? I find that impacts the result significantly. — bradkratky
I can't manage the font params. What I did that improves significantly the result is, in the first image that I've posted, was making some dilations and then passing it to the tesseract — user3368457

Unknown Unknown · Accepted Answer · 2016-07-28T13:56:27

I noticed that with some dilations, the result ORC result is improved incredible well! For me, it was the solution

Improve quality of tesseract ocr result

1 Answers