Dash Detector

Detects and interprets sequences of dash characters as lines within a document image.

Remarks

The Dash Detector enables Grooper to recognize dashed lines—such as those used for signature lines, table borders, or form separators—by analyzing the spatial arrangement and characteristics of dash-like marks in the image.

This class is typically used as part of an image preprocessing pipeline, where it supplements standard line detection by identifying lines that are not solid but are instead composed of repeated dash segments. The detection process is configurable, allowing you to control the minimum number of dashes required to form a line and the maximum allowable gap between dashes.

How Dash Detection Works

The Dash Detector scans the image for clusters of dash-shaped blobs that are sufficiently aligned and spaced to be considered a line. It evaluates both horizontal and vertical orientations, filtering out noise and short or irregular sequences. When a valid dash sequence is found, it is treated as a line for the purposes of downstream processing, such as table extraction or form field recognition.

Configuration Guidance

• Use the 'Minimum Segment Length' property to specify how many dashes must be present in a sequence for it to be considered a line. Increasing this value reduces false positives from short or accidental dash groupings.
• Use the 'Maximum Dash Spacing' property to control how much space is allowed between dashes. This helps distinguish between intentional dashed lines and scattered marks.

The Dash Detector is most effective on documents where dashed lines are used for structure or guidance, and where consistent dash size and spacing can be expected. For best results, ensure that the image is properly binarized and free of excessive noise before applying dash detection.

Properties

Name	Type		Description
Minimum Segment Length	Int32	►	The minimum number of dash segments required for a sequence to be detected as a line. Default5 The 'Minimum Segment Length' property determines how many individual dash marks must be present in a contiguous sequence for it to be recognized as a line by the Dash Detector. This helps filter out short or accidental groupings of dashes that do not represent meaningful lines. Set this value higher to require longer dash sequences, which reduces the likelihood of false positives from noise or small marks. Set this value lower to allow shorter dashed lines to be detected, which may be necessary for forms or documents with brief signature lines or short table borders. Example: If set to 5, only sequences of 5 or more dashes will be considered lines.
Maximum Dash Spacing	Double	►	The maximum allowable gap between dashes, expressed as a percentage of the dash width. ConverterPercent Converter Default150% The 'Maximum Dash Spacing' property controls how much empty space can exist between adjacent dashes in a sequence for them to be considered part of the same line. The value is specified as a percentage of the average dash width. Lower values require dashes to be closely spaced, which helps avoid connecting unrelated marks but may miss lines with wider gaps. Higher values allow for more widely spaced dashes to be grouped as a line, which can be useful for documents with loosely dashed lines but may increase the risk of false positives. Example: If set to 150%, the gap between dashes can be up to 150% of the dash width.

Used By

Line RemovalLine Detection