CODEWITHSUNDEEP
iosobjective-copencvresizetesseract
Nikhil Sridhar
Nikhil Sridhar

Reputation: 1740

Improving Tesseract OCR Quality Fails

I am currently using tesseract to scan receipts. The quality wasn't good so I read this article on how to improve it: https://github.com/tesseract-ocr/tesseract/wiki/ImproveQuality#noise-removal. I implemented resizing, deskewing(aligning), and gaussian blur. But none of them seem to have a positive effect on the accuracy of the OCR except the deskewing. Here is my code for resizing and gaussian blur. Am I doing anything wrong? If not, what else can I do to help?

Code: 

+(UIImage *) prepareImage: (UIImage *)image{

    //converts UIImage to Mat format
    Mat im = cvMatWithImage(image);

    //grayscale image
    Mat gray;
    cvtColor(im, gray, CV_BGR2GRAY);

    //deskews text
    //did not provide code because I know it works
    Mat preprocessed = preprocess2(gray);
    double skew = hough_transform(preprocessed, im);
    Mat rotated = rot(im,skew* CV_PI/180);

    //resize image
    Mat scaledImage = scaleImage(rotated, 2);

    //Guassian Blur
    GaussianBlur(scaledImage, scaledImage, cv::Size(1, 1), 0, 0);

    return UIImageFromCVMat(scaledImage);
}

// Organization -> Resizing

Mat scaleImage(Mat mat, double factor){
    Mat resizedMat;
    double width = mat.cols;
    double height = mat.rows;
    double aspectRatio = width/height;
    resize(mat, resizedMat, cv::Size(width*factor*aspectRatio, height*factor*aspectRatio));
    return resizedMat;
}

Receipt:

enter image description here

Upvotes: 1

Views: 589

Answers (1)

GeneCode
GeneCode

Reputation: 7588

If you read the Tesseract documentation you will see that tesseract engine works best with texts in a single line in a square. Passing it the whole receipt image reduces the engine's accuracy. What you need to do is use the new iOS framework CITextFeature to detect texts in your receipt into multiple blocks of images. Then only you can pass those images to tesseract for processing.

Upvotes: 1

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