Scoreboard digit recognition using OpenCV
I am trying to extract numbers from a typical scoreboard that you would find at a high school gym. I have each number in a digital "alarm clock" font and have managed to perspective correct, threshold and extract a given digit from the video feed
Here's a sample of my template input
My problem is that no one classification method will accurately determine all digits 0-9. I have tried several methods
1) Tesseract OCR - this one consistently messes up on 4 and frequently returns weird results. Just using the command line version. If I actually try to train it on an "alarm clock" font, I get unknown character every time.
2) kNearest with OpenCV - I search a database consisting of my template images (0-9) and see which one is nearest. I frequently get confusion between 3/1 and 7/1
3) cvMatchShapes - this one is fairly bad, it usually can't tell the difference between 2 of the digits for each input digit
4) Tangent Distance - This one is the closest, but the smallest tangent distance between the input and my templates ends up mapping "7" to "1" every time
I'm really at a loss to get a classification algorithm for such a simple problem. I feel I have cleaned up the input fairly well and it's a fairly simple case for classification but I can't get anything reliable enough to actually use in practice. Any ideas about where to look for classification algorithms, or how to use them correctly would be appreciated. Am I not cleaning up the input? What about a better input database? I don't know what else I'd use for input, each digit and template looks spot on at this point.
Answer
The classical digit recognition, which should work well in this case is to crop the image just around the digit and resize it to 4x4 pixels.
A Discrete Cosine Transform (DCT) can be used to further slim down the search space. You could select the first 4-6 values.
With those values, train a classifier. SVM is a good one, readily available in OpenCV.
It is not as simple as emma's or martin suggestions, but it's more elegant and, I think, more robust.
Given the width/height ratio of your input, you may choose a different resolution, like 3x4. Choose the smallest one that retains readable digits.