expand_domain_grayexpand_domain_grayExpandDomainGrayExpandDomainGray (Operator)

Name

expand_domain_grayexpand_domain_grayExpandDomainGrayExpandDomainGray — Expand the domain of an image and set the gray values in the expanded domain.

Signature

Description

expand_domain_grayexpand_domain_grayExpandDomainGrayExpandDomainGrayExpandDomainGray expands the border gray values of the domain outwards. The width of the expansion is set by the parameter ExpansionRangeExpansionRangeExpansionRangeExpansionRangeexpansionRange. All filters in HALCON use gray values of the pixels outside the domain depending on the filter width. This may lead to undesirable side effects especially in the border region of the domain. For example, if the foreground (domain) and the background of the image differ strongly in brightness, the result of a filter operation may lead to undesired darkening or brightening at the border of the domain. In order to avoid this drawback, the domain is expanded by expand_domain_grayexpand_domain_grayExpandDomainGrayExpandDomainGrayExpandDomainGray in a preliminary stage, copying the gray values of the border pixels to the outside of the domain. In addition, the domain itself is also expanded to reflect the newly set pixels. Therefore, in many cases it is reasonable to reduce the domain again (reduce_domainreduce_domainReduceDomainReduceDomainReduceDomain or change_domainchange_domainChangeDomainChangeDomainChangeDomain) after using expand_domain_grayexpand_domain_grayExpandDomainGrayExpandDomainGrayExpandDomainGray and call the filter operation afterwards. ExpansionRangeExpansionRangeExpansionRangeExpansionRangeexpansionRange should be set to the half of the filter width.

Attention

Note that filter operators may return unexpected results if an image with a reduced domain is used as input. Please refer to the chapter Filters.

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)

read_image(Fabrik, 'fabrik')
gen_rectangle2(Rectangle_Label,243,320,-1.55,62,28)
reduce_domain(Fabrik, Rectangle_Label, Fabrik_Label)
* Character extraction without gray value expansion:
mean_image(Fabrik_Label,Label_Mean_normal,31,31)
dyn_threshold(Fabrik_Label,Label_Mean_normal,Characters_normal,10,'dark')
dev_display(Fabrik)
dev_display(Characters_normal)
* The characters in the border region are not extracted !
stop()
* Character extraction with gray value expansion:
expand_domain_gray(Fabrik_Label, Label_expanded,15)
reduce_domain(Label_expanded,Rectangle_Label, Label_expanded_reduced)
mean_image(Label_expanded_reduced,Label_Mean_expanded,31,31)
dyn_threshold(Fabrik_Label,Label_Mean_expanded,\
              Characters_expanded,10,'dark')
dev_display(Fabrik)
dev_display(Characters_expanded)
* Now, even in the border region the characters are recognized

Complexity

Let L the perimeter of the domain. Then the runtime complexity is approximately O(L)*ExpansionRangeExpansionRangeExpansionRangeExpansionRangeexpansionRange.

Result

expand_domain_grayexpand_domain_grayExpandDomainGrayExpandDomainGrayExpandDomainGray returns 2 (H_MSG_TRUE) if all parameters are correct. If necessary, an exception is raised.

Possible Predecessors

reduce_domainreduce_domainReduceDomainReduceDomainReduceDomain

Possible Successors

reduce_domainreduce_domainReduceDomainReduceDomainReduceDomain, mean_imagemean_imageMeanImageMeanImageMeanImage, dyn_thresholddyn_thresholdDynThresholdDynThresholdDynThreshold

See also

reduce_domainreduce_domainReduceDomainReduceDomainReduceDomain, mean_imagemean_imageMeanImageMeanImageMeanImage

Module

Foundation