Grooper Help - Version 25.0
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Halftone Removal

Binary Dropout Grooper.IP

Removes halftone regions from an image to improve OCR and document clarity.

Remarks

The Halftone Removal command detects and removes halftone patterns—matrices of small dots used to simulate shades of gray— from document images. Halftone patterns are commonly found in shaded table headers, section headers, or background fills, and can prevent OCR engines from recognizing text printed within these regions.

A halftone pattern is illustrated below:

Sample Halftone

How Halftone Removal Works

  1. The input image is binarized using the settings defined in the 'Binarization Settings' property.
  2. Small specks (dots) are detected based on size and connectivity.
  3. Specks are grouped into candidate halftone regions using spacing and region size criteria.
  4. Regions are classified as bound (enclosed by lines) or unbound, and only those meeting minimum area and size requirements are masked.
  5. The mask is applied to the original image, removing halftone regions and improving text clarity for OCR.

Configuration and Usage

  • Adjust the 'Maximum Speck Size' and 'Speck Connectivity' properties to accurately detect halftone dots.
  • Use 'Minimum Region Size', 'Minimum Region Area', and 'Maximum Spacing' to control which regions are considered halftone.
  • Review the "Specks", "Candidates", and "Regions" diagnostic images to ensure correct detection and removal.
  • This command is typically used as a pre-OCR cleanup step to improve recognition of text printed inside shaded or patterned regions.

Supported Pixel Formats

All common pixel formats are supported, including Pixel8bppGrayscale, Pixel24bppBgr, and Pixel1bppIndexed. Images are automatically converted as needed for halftone detection and removal.

Diagnostics

When run in diagnostic mode, Halftone Removal generates diagnostic images such as Specks, Candidates, Regions, and Final Mask. These help you tune detection parameters and verify that only the intended halftone regions are being removed.

Notes

  • Overly aggressive settings may remove non-halftone content. Always review diagnostic output to avoid unintentional data loss.
  • Halftone Removal does not generate classification features directly, but the results can impact downstream extraction and analysis.

Properties

NameTypeDescription
General
Image Preprocessing
Command Info

See Also

Used By

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