How to Get C# OCR Read Confidence with IronOCR

How Do I Get Read Confidence in C#?

After performing OCR on the input image, the confidence level of the text is stored in the Confidence property. Utilize the 'using' statement to automatically dispose of objects after use. Add documents such as images and PDFs with the OcrImageInput and OcrPdfInput classes, respectively. The Read method will return an OcrResult object that allows access to the Confidence property.

:path=/static-assets/ocr/content-code-examples/how-to/tesseract-result-confidence-get-confidence.cs

using IronOcr;

// Instantiate IronTesseract
IronTesseract ocrTesseract = new IronTesseract();

// Add image
using var imageInput = new OcrImageInput("sample.tiff");
// Perform OCR
OcrResult ocrResult = ocrTesseract.Read(imageInput);

// Get confidence level
double confidence = ocrResult.Confidence;

The confidence value returned ranges from 0 to 100, where:

• 90-100: Excellent confidence - Text is highly reliable
• 80-89: Good confidence - Text is generally accurate with minor uncertainties
• 70-79: Moderate confidence - Text may contain some errors
• Below 70: Low confidence - Text should be reviewed or reprocessed

How Can I Get Confidence at Different Levels?

Not only can you retrieve the confidence level of the entire document, but you can also access the confidence levels of each page, paragraph, line, word, and character. Furthermore, you can obtain the confidence of a block, which represents a collection of one or more paragraphs located closely together.

:path=/static-assets/ocr/content-code-examples/how-to/tesseract-result-confidence-confidence-level.cs

// Get page confidence level
double pageConfidence = ocrResult.Pages[0].Confidence;

// Get paragraph confidence level
double paragraphConfidence = ocrResult.Paragraphs[0].Confidence;

// Get line confidence level
double lineConfidence = ocrResult.Lines[0].Confidence;

// Get word confidence level
double wordConfidence = ocrResult.Words[0].Confidence;

// Get character confidence level
double characterConfidence = ocrResult.Characters[0].Confidence;

// Get block confidence level
double blockConfidence = ocrResult.Blocks[0].Confidence;

using IronOcr;
using System.Linq;

// Instantiate IronTesseract
IronTesseract ocrTesseract = new IronTesseract();

// Configure for better accuracy
ocrTesseract.Configuration.ReadBarCodes = false;
ocrTesseract.Configuration.PageSegmentationMode = TesseractPageSegmentationMode.AutoOsd;

// Add image
using var imageInput = new OcrImageInput("invoice.png");
// Apply filters to improve quality
imageInput.Deskew();
imageInput.DeNoise();

// Perform OCR
OcrResult ocrResult = ocrTesseract.Read(imageInput);

// Filter words with confidence above 85%
var highConfidenceWords = ocrResult.Words
    .Where(word => word.Confidence >= 85)
    .Select(word => word.Text)
    .ToList();

// Process only high-confidence text
string reliableText = string.Join(" ", highConfidenceWords);
Console.WriteLine($"High confidence text: {reliableText}");

// Flag low-confidence words for manual review
var lowConfidenceWords = ocrResult.Words
    .Where(word => word.Confidence < 85)
    .Select(word => new { word.Text, word.Confidence })
    .ToList();

foreach (var word in lowConfidenceWords)
{
    Console.WriteLine($"Review needed: '{word.Text}' (Confidence: {word.Confidence:F2}%)");
}

using IronOcr;
using System.Linq;

// Instantiate IronTesseract
IronTesseract ocrTesseract = new IronTesseract();

// Configure for better accuracy
ocrTesseract.Configuration.ReadBarCodes = false;
ocrTesseract.Configuration.PageSegmentationMode = TesseractPageSegmentationMode.AutoOsd;

// Add image
using var imageInput = new OcrImageInput("invoice.png");
// Apply filters to improve quality
imageInput.Deskew();
imageInput.DeNoise();

// Perform OCR
OcrResult ocrResult = ocrTesseract.Read(imageInput);

// Filter words with confidence above 85%
var highConfidenceWords = ocrResult.Words
    .Where(word => word.Confidence >= 85)
    .Select(word => word.Text)
    .ToList();

// Process only high-confidence text
string reliableText = string.Join(" ", highConfidenceWords);
Console.WriteLine($"High confidence text: {reliableText}");

// Flag low-confidence words for manual review
var lowConfidenceWords = ocrResult.Words
    .Where(word => word.Confidence < 85)
    .Select(word => new { word.Text, word.Confidence })
    .ToList();

foreach (var word in lowConfidenceWords)
{
    Console.WriteLine($"Review needed: '{word.Text}' (Confidence: {word.Confidence:F2}%)");
}

What Are Character Choices in OCR?

Apart from the confidence level, there is another interesting property called Choices. Choices contain a list of alternative word choices and their statistical relevance. This information allows the user to access other possible characters. This feature is particularly useful when working with multiple languages or specialized fonts.

:path=/static-assets/ocr/content-code-examples/how-to/tesseract-result-confidence-get-choices.cs

using IronOcr;
using static IronOcr.OcrResult;

// Instantiate IronTesseract
IronTesseract ocrTesseract = new IronTesseract();

// Add image
using var imageInput = new OcrImageInput("Potter.tiff");
// Perform OCR
OcrResult ocrResult = ocrTesseract.Read(imageInput);

// Get choices
Choice[] choices = ocrResult.Characters[0].Choices;

How Do Alternative Character Choices Help?

Alternative character choices provide several benefits:

1. Ambiguity Resolution: When characters like 'O' and '0', or 'l' and '1' are confused
2. Font Variations: Different interpretations for stylized or decorative fonts
3. Quality Issues: Multiple possibilities when dealing with degraded text
4. Language Context: Alternative interpretations based on language rules

using IronOcr;
using System;
using System.Linq;
using static IronOcr.OcrResult;

// Configure IronTesseract for detailed results
IronTesseract ocrTesseract = new IronTesseract();

// Process image with potential ambiguities
using var imageInput = new OcrImageInput("ambiguous_text.png");
OcrResult ocrResult = ocrTesseract.Read(imageInput);

// Analyze character choices for each word
foreach (var word in ocrResult.Words)
{
    Console.WriteLine($"\nWord: '{word.Text}' (Confidence: {word.Confidence:F2}%)");

    // Check each character in the word
    foreach (var character in word.Characters)
    {
        if (character.Choices != null && character.Choices.Length > 1)
        {
            Console.WriteLine($"  Character '{character.Text}' has alternatives:");

            // Display all choices sorted by confidence
            foreach (var choice in character.Choices.OrderByDescending(c => c.Confidence))
            {
                Console.WriteLine($"    - '{choice.Text}': {choice.Confidence:F2}%");
            }
        }
    }
}

using IronOcr;
using System;
using System.Linq;
using static IronOcr.OcrResult;

// Configure IronTesseract for detailed results
IronTesseract ocrTesseract = new IronTesseract();

// Process image with potential ambiguities
using var imageInput = new OcrImageInput("ambiguous_text.png");
OcrResult ocrResult = ocrTesseract.Read(imageInput);

// Analyze character choices for each word
foreach (var word in ocrResult.Words)
{
    Console.WriteLine($"\nWord: '{word.Text}' (Confidence: {word.Confidence:F2}%)");

    // Check each character in the word
    foreach (var character in word.Characters)
    {
        if (character.Choices != null && character.Choices.Length > 1)
        {
            Console.WriteLine($"  Character '{character.Text}' has alternatives:");

            // Display all choices sorted by confidence
            foreach (var choice in character.Choices.OrderByDescending(c => c.Confidence))
            {
                Console.WriteLine($"    - '{choice.Text}': {choice.Confidence:F2}%");
            }
        }
    }
}

Advanced Confidence Strategies

When working with specialized documents like passports, license plates, or MICR cheques, confidence scores become crucial for validation:

using IronOcr;

public class DocumentValidator
{
    private readonly IronTesseract ocr = new IronTesseract();

    public bool ValidatePassportNumber(string imagePath, double minConfidence = 95.0)
    {
        using var input = new OcrImageInput(imagePath);

        // Configure for passport reading
        ocr.Configuration.ReadBarCodes = true;
        ocr.Configuration.PageSegmentationMode = TesseractPageSegmentationMode.SingleLine;

        // Apply preprocessing
        input.Deskew();
        input.Scale(200); // Upscale for better accuracy

        var result = ocr.Read(input);

        // Find passport number pattern
        var passportLine = result.Lines
            .Where(line => line.Text.Contains("P<") || IsPassportNumberFormat(line.Text))
            .FirstOrDefault();

        if (passportLine != null)
        {
            Console.WriteLine($"Passport line found: {passportLine.Text}");
            Console.WriteLine($"Confidence: {passportLine.Confidence:F2}%");

            // Only accept if confidence meets threshold
            return passportLine.Confidence >= minConfidence;
        }

        return false;
    }

    private bool IsPassportNumberFormat(string text)
    {
        // Simple passport number validation
        return System.Text.RegularExpressions.Regex.IsMatch(text, @"^[A-Z]\d{7,9}$");
    }
}

using IronOcr;

public class DocumentValidator
{
    private readonly IronTesseract ocr = new IronTesseract();

    public bool ValidatePassportNumber(string imagePath, double minConfidence = 95.0)
    {
        using var input = new OcrImageInput(imagePath);

        // Configure for passport reading
        ocr.Configuration.ReadBarCodes = true;
        ocr.Configuration.PageSegmentationMode = TesseractPageSegmentationMode.SingleLine;

        // Apply preprocessing
        input.Deskew();
        input.Scale(200); // Upscale for better accuracy

        var result = ocr.Read(input);

        // Find passport number pattern
        var passportLine = result.Lines
            .Where(line => line.Text.Contains("P<") || IsPassportNumberFormat(line.Text))
            .FirstOrDefault();

        if (passportLine != null)
        {
            Console.WriteLine($"Passport line found: {passportLine.Text}");
            Console.WriteLine($"Confidence: {passportLine.Confidence:F2}%");

            // Only accept if confidence meets threshold
            return passportLine.Confidence >= minConfidence;
        }

        return false;
    }

    private bool IsPassportNumberFormat(string text)
    {
        // Simple passport number validation
        return System.Text.RegularExpressions.Regex.IsMatch(text, @"^[A-Z]\d{7,9}$");
    }
}

Optimizing for Better Confidence

To achieve higher confidence scores, consider using image filters and preprocessing techniques:

using IronOcr;

// Create an optimized OCR workflow
IronTesseract ocr = new IronTesseract();

using var input = new OcrImageInput("low_quality_scan.jpg");

// Apply multiple filters to improve confidence
input.Deskew();           // Correct rotation
input.DeNoise();          // Remove noise
input.Sharpen();          // Enhance edges
input.Dilate();           // Thicken text
input.Scale(150);         // Upscale for clarity

// Configure for accuracy over speed
ocr.Configuration.TesseractVersion = TesseractVersion.Tesseract5;
ocr.Configuration.EngineMode = TesseractEngineMode.TesseractOnly;

var result = ocr.Read(input);

Console.WriteLine($"Document confidence: {result.Confidence:F2}%");

// Generate confidence report
var confidenceReport = result.Pages
    .Select((page, index) => new
    {
        PageNumber = index + 1,
        Confidence = page.Confidence,
        WordCount = page.Words.Length,
        LowConfidenceWords = page.Words.Count(w => w.Confidence < 80)
    });

foreach (var page in confidenceReport)
{
    Console.WriteLine($"Page {page.PageNumber}: {page.Confidence:F2}% confidence");
    Console.WriteLine($"  Total words: {page.WordCount}");
    Console.WriteLine($"  Low confidence words: {page.LowConfidenceWords}");
}

using IronOcr;

// Create an optimized OCR workflow
IronTesseract ocr = new IronTesseract();

using var input = new OcrImageInput("low_quality_scan.jpg");

// Apply multiple filters to improve confidence
input.Deskew();           // Correct rotation
input.DeNoise();          // Remove noise
input.Sharpen();          // Enhance edges
input.Dilate();           // Thicken text
input.Scale(150);         // Upscale for clarity

// Configure for accuracy over speed
ocr.Configuration.TesseractVersion = TesseractVersion.Tesseract5;
ocr.Configuration.EngineMode = TesseractEngineMode.TesseractOnly;

var result = ocr.Read(input);

Console.WriteLine($"Document confidence: {result.Confidence:F2}%");

// Generate confidence report
var confidenceReport = result.Pages
    .Select((page, index) => new
    {
        PageNumber = index + 1,
        Confidence = page.Confidence,
        WordCount = page.Words.Length,
        LowConfidenceWords = page.Words.Count(w => w.Confidence < 80)
    });

foreach (var page in confidenceReport)
{
    Console.WriteLine($"Page {page.PageNumber}: {page.Confidence:F2}% confidence");
    Console.WriteLine($"  Total words: {page.WordCount}");
    Console.WriteLine($"  Low confidence words: {page.LowConfidenceWords}");
}

Summary

Understanding and utilizing OCR confidence scores is essential for building robust document processing applications. By leveraging IronOCR's confidence properties and character choices, developers can implement intelligent validation, error handling, and quality assurance mechanisms in their OCR workflows. Whether you're processing screenshots, tables, or specialized documents, confidence scores provide the metrics needed to ensure accurate text extraction.