How to Fix Image Colors for Reading in C#

How Can I Export and Compare Results?

Export modified images using the SaveAsImages method. Compare images before and after binarization below.

Before

After

When Should I Use Grayscale Over Other Methods?

Apply grayscale using the ToGrayScale method. The process averages R, G, and B values.

Grayscale works well with colored backgrounds or watermarks that interfere with text recognition. Unlike binarization, grayscale preserves detail in images with subtle variations. Use it for photographs with embedded text or complex layouts. For low-quality scans, see Fixing Low Quality Scans & Images.

What Is the Simple Code for Grayscale Conversion?

:path=/static-assets/ocr/content-code-examples/how-to/image-color-correction-grayscale-image.cs

// Apply grayscale affect
imageInput.ToGrayScale();

For varied image qualities, combine grayscale with other preprocessing steps. The OcrInput Class documentation explains chaining multiple filters.

How Does Grayscale Compare to the Original?

Before

After

How Do I Implement Color Inversion?

Use the Invert method to invert colors. Pass a boolean value to remove color channels and return grayscale.

Color inversion handles negative images or dark-themed screenshots. Modern applications use dark mode interfaces that challenge traditional OCR. Inverting these images ensures optimal recognition. For various image types, see the Fast OCR Configuration guide.

:path=/static-assets/ocr/content-code-examples/how-to/image-color-correction-invert-image.cs

// Apply invert affect
imageInput.Invert();

For batch processing with mixed document types, implement automatic dark background detection. Computer Vision features in IronOCR identify when inversion is needed.

What Is the Difference Between Inversion Options?

Compare the Invert method with and without grayscale:

Inverted

Inverted & Grayscaled

Why Is Tolerance Important in Color Replacement?

The ReplaceColor method requires the current color, new color, and tolerance value. Higher tolerance handles blurry images better.

Tolerance determines how closely pixels must match your target color. Low values (0-50) suit uniform colors. Higher values (100-200) handle anti-aliased text or compression artifacts. This helps with scanned documents where ink bleeding or paper texture creates variations.

How Do I Implement Color Replacement?

:path=/static-assets/ocr/content-code-examples/how-to/image-color-correction-replace-color.cs

using IronOcr;

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

// Add image
using var imageInput = new OcrImageInput("sample.jpg");
IronSoftware.Drawing.Color currentColor = new IronSoftware.Drawing.Color("#DB645C");
IronSoftware.Drawing.Color newColor = IronSoftware.Drawing.Color.DarkCyan;

// Replace color
imageInput.ReplaceColor(currentColor, newColor, 80);

// Export the modified image
imageInput.SaveAsImages("replaceColor");

How Do I Handle Advanced Color Replacement Scenarios?

Chain multiple replacements for complex scenarios:

/* :path=/static-assets/ocr/content-code-examples/how-to/image-color-correction-multiple-replacements.cs */
// Replace multiple colors in sequence
using var imageInput = new OcrImageInput("multi-color-document.jpg");

// Replace red text with black
imageInput.ReplaceColor(IronSoftware.Drawing.Color.Red, IronSoftware.Drawing.Color.Black, 70);

// Replace blue headers with dark gray
imageInput.ReplaceColor(IronSoftware.Drawing.Color.Blue, IronSoftware.Drawing.Color.DarkGray, 60);

// Replace light yellow background with white
imageInput.ReplaceColor(new IronSoftware.Drawing.Color("#FFFACD"), IronSoftware.Drawing.Color.White, 40);

// Perform OCR on the cleaned image
var result = ocrTesseract.Read(imageInput);

/* :path=/static-assets/ocr/content-code-examples/how-to/image-color-correction-multiple-replacements.cs */
// Replace multiple colors in sequence
using var imageInput = new OcrImageInput("multi-color-document.jpg");

// Replace red text with black
imageInput.ReplaceColor(IronSoftware.Drawing.Color.Red, IronSoftware.Drawing.Color.Black, 70);

// Replace blue headers with dark gray
imageInput.ReplaceColor(IronSoftware.Drawing.Color.Blue, IronSoftware.Drawing.Color.DarkGray, 60);

// Replace light yellow background with white
imageInput.ReplaceColor(new IronSoftware.Drawing.Color("#FFFACD"), IronSoftware.Drawing.Color.White, 40);

// Perform OCR on the cleaned image
var result = ocrTesseract.Read(imageInput);

For complex color replacements, see Image Correction Filters for additional preprocessing techniques.

What Are the Visual Results of Color Replacement?

Before

After

How Does Color Tolerance Affect Results?

:path=/static-assets/ocr/content-code-examples/how-to/image-color-correction-select-text-color.cs

using IronOcr;
using System;

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

// Add image
using var imageInput = new OcrImageInput("sample.jpg");
// Text color to focus on
IronSoftware.Drawing.Color focusColor = new IronSoftware.Drawing.Color("#DB645C");

// Specify which text color to read
imageInput.SelectTextColor(focusColor, 60);

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

// Output result to console
Console.WriteLine(ocrResult.Text);

Use selective color reading for forms with color-coded sections, extracting highlighted text, or reading specific warning messages. For structured data extraction, see OcrResult Class for advanced processing.

What Output Can I Expect from Color Selection?

The OCR result reads only orange-colored text:

What Is the Implementation for Searchable PDFs?

:path=/static-assets/ocr/content-code-examples/how-to/image-quality-correction-searchable-pdf.cs

using IronOcr;

var ocr = new IronTesseract();
var ocrInput = new OcrInput();

// Load a PDF file
ocrInput.LoadPdf("invoice.pdf");

// Apply gray scale filter
ocrInput.ToGrayScale();
OcrResult result = ocr.Read(ocrInput);

// Save the result as a searchable PDF with filters applied
result.SaveAsSearchablePdf("outputGrayscale.pdf", true);

When Should I Apply Filters to the Saved PDF?

Apply filters when creating cleaner, more readable documents. This helps with archival purposes or sharing documents across different devices. See Create Searchable PDFs by OCR for more information.

For complex documents with tables, explore Read Table in Document for specialized extraction. For high-volume processing, see Multithreaded Tesseract OCR to optimize filter application across multiple documents.