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Here are some sample images:

In order to get better answer. Here are some sample pictures:

Wow, thanks for your help! So you say it's not necessary to crop the image? Then I consider doing some image processing and then a template matching..

Which template matching method do you use in your project? cv2.matchTemplate()? An then train your algorithm? Did you find some helpful tutorials for your project?

Thanks for respond. I've already done some open-closing tutorials as well as cv2.bilateralFilter() and cv2.equalizeHist() for noise reduction.

Now i'm getting a nearly "noisless" image. But the main problem is, that i have to separate the black-white part (roman numeral and white background) from the scene image. Would you use the crop() function or do you think this is not a necessary step in order to detect the roman numeral?

You're right, reading numerals is the main goal, but I think ocr tesseract is not robust enough, considering that we talk about roman numerals with serif. I did some tutorials with ocr tesseract and it doesn't work well (just a small success rate). Don't you think cv2.matchTemplate would be more appropriate? Or like I mentioned counting corners or lines?

Hi there I'm new in OpenCV and Python/C++. I've already worked through the tutorials on this site and now wanted to do some own exercices with OpenCV 2.4 and Python 2.7. I would like to recognize a black colored roman numeral (e.g. I, II, III, IV, V, ...) on a white background in an image and try to get a value according to this roman numeral.

I've already tried some OpenCV techniques like: - harrisCorner (counting the corners of the black "object" and return the value in an if-else contruct) e.g. roman numeral I has 12 corners (considering the serifs). - roughlines (counting long horizontal and vertical lines in the image and return the value in an if-else contruct) - templateMatching (compare the "scene" image with a template image of a roman numeral)

In simple cases these techniques are working. But most of the images contain noise and the matching fails. I think i should do image processing before to crop the black numeral and white background out of the image.

So my questions are: - Do you think these techniques or especially one would be good to detect the roman numeral? - Are there any image processing tutorials to extract a black object on a white background?

There are some examples:

Thanks for help