Code samples

using System;
using System.Collections.Generic;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // convert an image-only PDF document to a searchable PDF document
            ConvertImageOnlyPdfToSearchablePdf(
                "imageOnlyPdfDocument.pdf",
                Vintasoft.Imaging.Ocr.OcrLanguage.English,
                "searchablePdfDocument.pdf");
        }

        /// <summary>
        /// Converts an image-only PDF document to a searchable PDF document.
        /// </summary>
        /// <param name="imageOnlyPdfFilename">A filename of source image-only PDF file.</param>
        /// <param name="ocrLanguage">OCR language.</param>
        /// <param name="searchablePdfFilename">A filename of destination searchable PDF file.</param>
        public static void ConvertImageOnlyPdfToSearchablePdf(
            string imageOnlyPdfFilename,
            Vintasoft.Imaging.Ocr.OcrLanguage ocrLanguage,
            string searchablePdfFilename)
        {
            // create an image collection
            using (Vintasoft.Imaging.ImageCollection images = new Vintasoft.Imaging.ImageCollection())
            {
                // add pages from image-only PDF document into image collection
                images.Add(imageOnlyPdfFilename);

                // create a searchable PDF document
                using (Vintasoft.Imaging.Pdf.PdfDocument document =
                    new Vintasoft.Imaging.Pdf.PdfDocument(searchablePdfFilename, Vintasoft.Imaging.Pdf.PdfFormat.Pdf_14))
                {
                    Console.WriteLine("Create OCR engine...");
                    // create the Tesseract OCR engine
                    using (Vintasoft.Imaging.Ocr.Tesseract.TesseractOcr tesseractOcr =
                        new Vintasoft.Imaging.Ocr.Tesseract.TesseractOcr(@"..\..\TesseractOCR\"))
                    {
                        Console.WriteLine("Initialize OCR engine...");
                        // init the Tesseract OCR engine
                        tesseractOcr.Init(new Vintasoft.Imaging.Ocr.OcrEngineSettings(ocrLanguage));

                        // create a PDF document builder
                        Vintasoft.Imaging.Pdf.Ocr.PdfDocumentBuilder documentBuilder =
                            new Vintasoft.Imaging.Pdf.Ocr.PdfDocumentBuilder(document);
                        // specify that the best image compression must be calculated automatically
                        documentBuilder.ImageCompression = Vintasoft.Imaging.Pdf.PdfCompression.Auto;
                        // specify that image must be place over text
                        documentBuilder.PageCreationMode = Vintasoft.Imaging.Pdf.Ocr.PdfPageCreationMode.ImageOverText;

                        // for each image in image collection
                        foreach (Vintasoft.Imaging.VintasoftImage image in images)
                        {
                            Console.WriteLine("Recognize text in image...");
                            // recognize text on image
                            Vintasoft.Imaging.Ocr.Results.OcrPage ocrPage = tesseractOcr.Recognize(image);

                            // remove low confidence words from OCR result
                            RemoveLowConfidenceWords(ocrPage);

                            Console.WriteLine("Add page to a PDF document...");
                            // add recognized OCR page to the PDF document
                            documentBuilder.AddPage(image, ocrPage);
                        }

                        // shutdown OCR engine
                        tesseractOcr.Shutdown();

                        Console.WriteLine("Save changes in PDF document...");
                        // save changes in PDF document
                        document.SaveChanges();
                    }
                }

                // clear and dispose images in image collection
                images.ClearAndDisposeItems();
            }
        }

        /// <summary>
        /// Preprocess an image before text recognition.
        /// </summary>
        /// <param name="image">Image to preprocess.</param>
        static void PreprocessImageBeforeOcr(Vintasoft.Imaging.VintasoftImage image)
        {
            // remove noise from image
            Vintasoft.Imaging.ImageProcessing.Document.DespeckleCommand despeckleCommand =
                new Vintasoft.Imaging.ImageProcessing.Document.DespeckleCommand();
            despeckleCommand.ExecuteInPlace(image);
        }

        /// <summary>
        /// Removes low confidence words from OCR page.
        /// </summary>
        /// <param name="ocrPage">OCR page.</param>
        static void RemoveLowConfidenceWords(Vintasoft.Imaging.Ocr.Results.OcrPage ocrPage)
        {
            // minimum confidence
            const float MIN_CONFIDENCE = 75.0f;

            // get all words in recognized text
            Vintasoft.Imaging.Ocr.Results.OcrObject[] ocrObjects =
                ocrPage.GetObjects(Vintasoft.Imaging.Ocr.OcrObjectType.Word);
            // create list of words to remove
            List<Vintasoft.Imaging.Ocr.Results.OcrObject> removeObjects =
                new List<Vintasoft.Imaging.Ocr.Results.OcrObject>();
            // for each word
            foreach (Vintasoft.Imaging.Ocr.Results.OcrObject word in ocrObjects)
            {
                // if word confidence is less than minimum confidence
                if (word.Confidence < MIN_CONFIDENCE)
                    // add word to a list of words to remove
                    removeObjects.Add(word);
            }

            // validate recognition results (remove words with low confidence)

            Vintasoft.Imaging.Ocr.Results.OcrResultsEditor editor =
                new Vintasoft.Imaging.Ocr.Results.OcrResultsEditor(ocrPage);
            editor.RemoveObjects(removeObjects.ToArray());
            editor.ValidateResults();
        }

    }
}