select_charactersT_select_charactersSelectCharactersSelectCharactersselect_characters (Operator)

Name

select_charactersT_select_charactersSelectCharactersSelectCharactersselect_characters — Selects characters from a given region.

Signature

Description

select_charactersselect_charactersSelectCharactersSelectCharactersselect_characters selects from a given RegionRegionRegionregionregion the areas which might be characters and returns them in RegionCharactersRegionCharactersRegionCharactersregionCharactersregion_characters. This is done by using features like StrokeWidthStrokeWidthStrokeWidthstrokeWidthstroke_width, DotPrintDotPrintDotPrintdotPrintdot_print, the size of the characters and some more. The given RegionRegionRegionregionregion should be united, else every RegionRegionRegionregionregion is processed separately. Thus do not call connectionconnectionConnectionConnectionconnection before calling select_charactersselect_charactersSelectCharactersSelectCharactersselect_characters, because then fragments or dots would not be connected to a character. If you have more than one region with text, you can of course handle them without merging them. The RegionRegionRegionregionregion for select_charactersselect_charactersSelectCharactersSelectCharactersselect_characters typically comes from segment_characterssegment_charactersSegmentCharactersSegmentCharacterssegment_characters but also any other segmentation operators can be used.

The process of the selection can be partitioned into four parts. All steps are influenced by the parameters StrokeWidthStrokeWidthStrokeWidthstrokeWidthstroke_width, CharHeightCharHeightCharHeightcharHeightchar_height, and CharWidthCharWidthCharWidthcharWidthchar_width. If you loose small objects like dots, adapt the minimum CharWidthCharWidthCharWidthcharWidthchar_width and the minimum CharHeightCharHeightCharHeightcharHeightchar_height. But some parameters affect the result of a certain step in particular. A closer description follows below. With the parameter StopAfterStopAfterStopAfterstopAfterstop_after you can terminate after a specified step.

In the first step, 'step1_select_candidates'"step1_select_candidates""step1_select_candidates""step1_select_candidates""step1_select_candidates", CharWidthCharWidthCharWidthcharWidthchar_width and the CharHeightCharHeightCharHeightcharHeightchar_height are used to select the candidates. The result of this step is also affected by ClutterSizeMaxClutterSizeMaxClutterSizeMaxclutterSizeMaxclutter_size_max.

In the next step, 'step2_partition_characters'"step2_partition_characters""step2_partition_characters""step2_partition_characters""step2_partition_characters", the parameter PartitionMethodPartitionMethodPartitionMethodpartitionMethodpartition_method and the parameter PartitionLinesPartitionLinesPartitionLinespartitionLinespartition_lines influence the result.

Step three, 'step3_connect_fragments'"step3_connect_fragments""step3_connect_fragments""step3_connect_fragments""step3_connect_fragments", uses the parameters ConnectFragmentsConnectFragmentsConnectFragmentsconnectFragmentsconnect_fragments and DotPrintDotPrintDotPrintdotPrintdot_print. If dot-printed characters have to be detected and some dots are not connected to the character, there are two ways to overcome this problem: You can increase the FragmentDistanceFragmentDistanceFragmentDistancefragmentDistancefragment_distance and/or decrease the StrokeWidthStrokeWidthStrokeWidthstrokeWidthstroke_width.

In the last step, 'step4_select_characters'"step4_select_characters""step4_select_characters""step4_select_characters""step4_select_characters", the result is affected by the parameters DiacriticMarksDiacriticMarksDiacriticMarksdiacriticMarksdiacritic_marks and PunctuationPunctuationPunctuationpunctuationpunctuation.

DotPrintDotPrintDotPrintdotPrintdot_print: Should be set to 'true'"true""true""true""true" if dot prints should be read, else to 'false'"false""false""false""false".

StrokeWidthStrokeWidthStrokeWidthstrokeWidthstroke_width: Specifies the stroke width of the text. It is used to calculate internally used mask sizes to determine the characters. This mask sizes are also influenced through the parameters DotPrintDotPrintDotPrintdotPrintdot_print, the average CharWidthCharWidthCharWidthcharWidthchar_width, and the average CharHeightCharHeightCharHeightcharHeightchar_height.

CharWidthCharWidthCharWidthcharWidthchar_width: This can be a tuple with up to three values. The first value is the average width of a character. The second is the minimum width of a character and the third is the maximum width of a character. If the minimum is not set or equal -1, the operator automatically sets these value depending on average CharWidthCharWidthCharWidthcharWidthchar_width. The same is the case if the maximum is not set. Some examples:

[10] sets the average character width to 10, the minimum and maximum are calculated by the operator.

[10,-1,20] sets the average character width to 10, the minimum value is calculated by the system, and the maximum is set to 20.

[10,5,20] sets the average character width to 10, the minimum to 5, and the maximum to 20.

CharHeightCharHeightCharHeightcharHeightchar_height: This can be a tuple with up to three values. The first value is the average height of a character. The second is the minimum height of a character and the third is the maximum height of a character. If the minimum is not set or equal -1, the operator automatically sets these value depending on average CharHeightCharHeightCharHeightcharHeightchar_height. The same is the case if the maximum is not set. Some examples:

[10] sets the average character height to 10, the minimum and maximum are calculated by the operator.

[10,-1,20] sets the average character height to 10 the minimum value is calculated by the system and the maximum is set to 20.

[10,5,20] this sets the average character height to 10, the minimum to 5 and the maximum to 20.

PunctuationPunctuationPunctuationpunctuationpunctuation: Set this parameter to 'true'"true""true""true""true" if the operator also has to detect punctuation marks (e.g., .,:'`"), otherwise they will be suppressed.

DiacriticMarksDiacriticMarksDiacriticMarksdiacriticMarksdiacritic_marks: Set this parameter to 'true'"true""true""true""true" if the text in your application contains diacritic marks (e.g., â,é,ö), or to 'false'"false""false""false""false" to suppress them.

PartitionMethodPartitionMethodPartitionMethodpartitionMethodpartition_method: If neighboring characters are printed close to each other, they may be partly merged. With this parameter you can specify the method to partition such characters. The possible values are 'none'"none""none""none""none", which means no partitioning is performed. 'fixed_width'"fixed_width""fixed_width""fixed_width""fixed_width" means that the partitioning assumes a constant character width. If the width of the extracted region is well above the average CharWidthCharWidthCharWidthcharWidthchar_width, the region is split into parts that have the given average CharWidthCharWidthCharWidthcharWidthchar_width. The partitioning starts at the left border of the region. 'variable_width'"variable_width""variable_width""variable_width""variable_width" means that the characters are partitioned at the position where they have the thinnest connection. This method can be selected for characters that are printed with a variable-width font or if many consecutive characters are extracted as one symbol. It could be helpful to call text_line_slanttext_line_slantTextLineSlantTextLineSlanttext_line_slant and/or use text_line_orientationtext_line_orientationTextLineOrientationTextLineOrientationtext_line_orientation before calling select_charactersselect_charactersSelectCharactersSelectCharactersselect_characters.

PartitionLinesPartitionLinesPartitionLinespartitionLinespartition_lines: If some text lines or some characters of different text lines are connected, set this parameter to 'true'"true""true""true""true".

FragmentDistanceFragmentDistanceFragmentDistancefragmentDistancefragment_distance: This parameter influences the connection of character fragments. If too much is connected, set the parameter to 'narrow'"narrow""narrow""narrow""narrow" or 'medium'"medium""medium""medium""medium". In the case that more fragments should be connected, set the parameter to 'medium'"medium""medium""medium""medium" or 'wide'"wide""wide""wide""wide". The connection is also influenced by the maximum of CharWidthCharWidthCharWidthcharWidthchar_width and CharHeightCharHeightCharHeightcharHeightchar_height. See also ConnectFragmentsConnectFragmentsConnectFragmentsconnectFragmentsconnect_fragments.

ConnectFragmentsConnectFragmentsConnectFragmentsconnectFragmentsconnect_fragments: Set this parameter to 'true'"true""true""true""true" if the extracted symbols are fragmented, i.e., if a symbol is not extracted as one region but broken up into several parts. See also FragmentDistanceFragmentDistanceFragmentDistancefragmentDistancefragment_distance and StopAfterStopAfterStopAfterstopAfterstop_after in the step 'step3_connect_fragments'"step3_connect_fragments""step3_connect_fragments""step3_connect_fragments""step3_connect_fragments".

ClutterSizeMaxClutterSizeMaxClutterSizeMaxclutterSizeMaxclutter_size_max: If the extracted characters contain clutter, i.e., small regions near the actual symbols, increase this value. If parts of the symbols are missing, decrease this value.

StopAfterStopAfterStopAfterstopAfterstop_after: Use this parameter in the case the operator does not produce the desired results. By modifying this value the operator stops after the execution of the selected step and provides the corresponding results. To end on completion, set StopAfterStopAfterStopAfterstopAfterstop_after to 'completion'"completion""completion""completion""completion".

Execution Information

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Automatically parallelized on tuple level.

Parameters

Example (HDevelop)

for Index := 1 to 5 by 1
  read_image (Image, 'dot_print_rotated/dot_print_rotated_'+Index$'02d')
  text_line_orientation (Image, Image, 50, rad(-30), rad(30), \
                         OrientationAngle)
  rotate_image (Image, ImageRotate, deg(-OrientationAngle), 'constant')
  segment_characters (ImageRotate, ImageRotate, ImageForeground, \
                      RegionForeground, 'local_auto_shape', 'false', \
                      'false', 'medium', 25, 25, 0, 10, UsedThreshold)
  select_characters (RegionForeground, RegionCharacters, 'true', \
                     'ultra_light', [60,1,100], [60,1,100], 'false', \
                     'false', 'none', 'true', 'wide', 'true', 0, 'completion')
endfor

Result

If the input parameters are set correctly, the operator select_charactersselect_charactersSelectCharactersSelectCharactersselect_characters returns the value 2 ( H_MSG_TRUE) . Otherwise an exception will be raised.

Possible Predecessors

segment_characterssegment_charactersSegmentCharactersSegmentCharacterssegment_characters, text_line_slanttext_line_slantTextLineSlantTextLineSlanttext_line_slant

Possible Successors

do_ocr_single_class_mlpdo_ocr_single_class_mlpDoOcrSingleClassMlpDoOcrSingleClassMlpdo_ocr_single_class_mlp, do_ocr_multi_class_mlpdo_ocr_multi_class_mlpDoOcrMultiClassMlpDoOcrMultiClassMlpdo_ocr_multi_class_mlp

Alternatives

connectionconnectionConnectionConnectionconnection

Module

Foundation

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