How to Correct Images Using Filters for Reading

Sharpen Filter Example

This filter increases the contrast along the edges in the image, giving them a more defined appearance. It improves the clarity of text and details, making it easier for OCR software to recognize characters.

To apply the sharpen filter, invoke the Sharpen method of the OcrImageInput object.

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

using IronOcr;

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

// Add image
using var imageInput = new OcrImageInput("sample.jpg");
// Apply sharpen filter
imageInput.Sharpen();

// Export filtered image
imageInput.SaveAsImages("sharpen.jpg");

Imports IronOcr

' Instantiate IronTesseract
Private ocrTesseract As New IronTesseract()

' Add image
Private imageInput = New OcrImageInput("sample.jpg")
' Apply sharpen filter
imageInput.Sharpen()

' Export filtered image
imageInput.SaveAsImages("sharpen.jpg")

For convenience, you can export the filtered image using the SaveAsImages method. Below is a comparison of the image before and after applying the sharpening filter.

Before

After

Enhance Resolution Filter Example

This filter is designed to increase the pixel density of an image, effectively improving its sharpness and clarity. It can be especially useful for enhancing the legibility of text in low-resolution images.

Invoke the EnhanceResolution method to apply the enhanced resolution filter. This method accepts the target DPI, with 225 DPI as the default value.

:path=/static-assets/ocr/content-code-examples/how-to/image-quality-correction-enhance-resolution-filter.cs

// Apply enhance resolution filter
imageInput.EnhanceResolution();

' Apply enhance resolution filter
imageInput.EnhanceResolution()

Before

After

Denoise Filter Example

Denoising filters reduce the level of noise or unwanted artifacts in an image. Noise reduction is crucial for OCR as it helps isolate text from background interference, leading to cleaner and more accurate recognition.

To apply the denoise filter, use the DeNoise method. The default morphology is 2x2. To apply a stronger denoise algorithm, pass 'true' to enable a 3x3 morphology.

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

// Apply denoise filter
imageInput.DeNoise();

' Apply denoise filter
imageInput.DeNoise()

Before

After

Dilate Filter Example

Dilation expands the brighter regions (foreground) in an image. It helps thicken and enhance the text, making it more prominent and easier for OCR software to interpret.

To apply the dilation filter, use the Dilate method. Default morphology is 2x2, and setting 'true' enables the 3x3 option.

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

// Apply dilate filter
imageInput.Dilate();

' Apply dilate filter
imageInput.Dilate()

Before

After

Erode Filter Example

Erosion reduces the size of bright regions in an image, useful for refining characters and lines, especially when they are thick or distorted.

Use the Erode method to apply the erode filter. As with previous methods, default morphology is 2x2, and setting 'true' enables 3x3.

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

// Apply erode filter
imageInput.Erode();

' Apply erode filter
imageInput.Erode()

Before

After

Searchable Pdfs

Other than the options for filtering images, IronOcr gives developers the flexibility of saving the modified PDF with the filters on or off. The SaveAsSearchablePdf method allows a boolean flag to be taken in as the second parameter to determine whether you want to save with filters or not.

: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);

IRON VB CONVERTER ERROR developers@ironsoftware.com