C# .net wrapper for tessnet

Question

I try to write wrapper for tessnet OCR library. I am getting an error saying "Cannot marshal 'return value': Generic types cannot be marshaled." for this code section

List<Word> k = OCRWrapper.DoOCR(new Bitmap(@"C:\Data\pdf2image\auto.png"), new Rectangle(0, 0, 55, 27));

My wrapper class is

class OCRWrapper
{
    [DllImport("TrueMarble.dll")]
    public static extern List<Word> DoOCR(Bitmap b, Rectangle rec);
}

please help me, can any one guide me to write this code

Thanx!

But tessnet is already a wrapper around tessaract in managed code. It also contains DoOCR method which can be used without importing. So what are you trying to do? What is a Word class in your code? — EvgK, Feb 08 '11 at 12:41

score 2 · Accepted Answer · answered Feb 08 '11 at 13:55

You are on the wrong track with this, Tessnet already is a managed class wrapper around Tesseract. You don't use [DllImport], just add a reference to the assembly and use the classes directly. Sample code and assembly download is available here.

Bitmap image = new Bitmap("eurotext.tif");
tessnet2.Tesseract ocr = new tessnet2.Tesseract();
ocr.SetVariable("tessedit_char_whitelist", "0123456789"); // If digit only
ocr.Init(@"c:\temp", "fra", false); // To use correct tessdata

List<tessnet2.Word> result = ocr.DoOCR(image, Rectangle.Empty);
foreach (tessnet2.Word word in result)
    Console.WriteLine("{0} : {1}", word.Confidence, word.Text);

@Hans-Passant when I run it it keep getting exiting without any output. why is that ? — yohan.jayarathna, Feb 09 '11 at 04:28

score 0 · Answer 2 · answered Feb 08 '11 at 11:50

0

Generic types could not be marshalled as they are native to .NET. use array of word instead

answered Feb 08 '11 at 11:50

Mubashir Khan

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honestly I tried it before. then I got this "Cannot marshal 'return value': Invalid managed/unmanaged type combination." – yohan.jayarathna Feb 08 '11 at 11:58

C# .net wrapper for tessnet

2 Answers2