tesseract cmd works but dotnet doesn't on same tif file

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29-08-2024

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Tesseract Working in Command Line but Not in .NET: A Common Pitfall and Its Solution

Many developers encounter the frustration of Tesseract OCR working flawlessly in the command line but producing gibberish when integrated into their .NET applications. This article will break down the common reasons behind this disparity and provide a clear solution based on insights from Stack Overflow.

Understanding the Problem:

The key lies in the tessdata folder, which contains the trained data for Tesseract to recognize different languages and symbols. While the command line version usually accesses the default tessdata folder, your .NET application needs to explicitly point to the correct location.

Common Causes and the Stack Overflow Solution:

Let's analyze the provided code snippet from a Stack Overflow question (link - replace with actual link), and pinpoint the error:

1. Incorrect Path: The code uses @"./tessdata", which assumes the tessdata folder is directly within the application's working directory. This might be incorrect, leading to Tesseract failing to find the necessary training data.

2. Ignoring the Default Path: Tesseract has a default location for its tessdata folder, and your command line execution likely relies on this default.

Solution:

To solve this, you need to ensure your .NET code uses the correct path to the tessdata folder. The Stack Overflow solution offered a simple but effective approach:

1. Use the TesseractEngine.Default Property: Instead of providing a relative path, leverage the TesseractEngine.Default property. This property points to the default tessdata location, ensuring compatibility with your command line execution.

Here's the updated code:

// Load the original bitmap from a file
Bitmap original = (Bitmap)System.Drawing.Image.FromFile(file);
// Create a new bitmap with the desired size
var ocrtext = string.Empty;
var path = Path.GetDirectoryName(Assembly.GetExecutingAssembly().CodeBase);
path = Path.Combine(path, "tessdata");
path = path.Replace("file:\\", "");
var result = "";
// get the ocr data 
using (var ocr = new TesseractEngine(TesseractEngine.Default, "eng", EngineMode.Default)) 
{
    ocr.SetVariable("tessedit_char_whitelist", "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ");
    {
        using (var img = PixConverter.ToPix(original))
        {
            using (var page = ocr.Process(img))
            {
                ocrtext = page.GetText();
                result = ocrtext.TrimStart('\n');
                using (StreamWriter sw = new StreamWriter(outfileab + ".txt"))
                {
                    sw.Write("aa:" + result);
                }
            }
        }
    }
}

Explanation:

• The code now uses TesseractEngine.Default as the first parameter for the TesseractEngine constructor, automatically directing Tesseract to the correct default tessdata location.

Key Takeaway:

The issue often stems from assuming the tessdata folder is located in the application's working directory when, in fact, Tesseract relies on a predefined default location. By leveraging the TesseractEngine.Default property, your .NET application will seamlessly integrate with the default Tesseract configuration, ensuring consistent behavior between your command line and .NET implementations.