expand_domain_grayexpand_domain_grayExpandDomainGrayExpandDomainGray (Operator)


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


expand_domain_gray(InputImage : ExpandedImage : ExpansionRange : )

Herror expand_domain_gray(const Hobject InputImage, Hobject* ExpandedImage, const Hlong ExpansionRange)

Herror T_expand_domain_gray(const Hobject InputImage, Hobject* ExpandedImage, const Htuple ExpansionRange)

void ExpandDomainGray(const HObject& InputImage, HObject* ExpandedImage, const HTuple& ExpansionRange)

HImage HImage::ExpandDomainGray(Hlong ExpansionRange) const

static void HOperatorSet.ExpandDomainGray(HObject inputImage, out HObject expandedImage, HTuple expansionRange)

HImage HImage.ExpandDomainGray(int expansionRange)


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 a value high enough to make sure the whole region including its dilatation through the filter mask has initialized values. Usually this leads to ExpansionRangeExpansionRangeExpansionRangeExpansionRangeexpansionRange values of half the filter length or greater. In combination with the filter mean_imagemean_imageMeanImageMeanImageMeanImage on images of type real we recommend to determine the value for ExpansionRangeExpansionRangeExpansionRangeExpansionRangeexpansionRange as shown in the example below. For speed reasons this filter uses the values from pixels within the smallest rectangle around the dilated region.


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


InputImageInputImageInputImageInputImageinputImage (input_object)  (multichannel-)image(-array) objectHImageHImageHobject (byte / int1 / int2 / uint2 / int4 / real)

Input image with domain to be expanded.

ExpandedImageExpandedImageExpandedImageExpandedImageexpandedImage (output_object)  image(-array) objectHImageHImageHobject * (byte / int1 / int2 / uint2 / int4 / real)

Output image with new gray values in the expanded domain.

ExpansionRangeExpansionRangeExpansionRangeExpansionRangeexpansionRange (input_control)  integer HTupleHTupleHtuple (integer) (int / long) (Hlong) (Hlong)

Radius of the gray value expansion, measured in pixels.

Default value: 2

Suggested values: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16

Restriction: ExpansionRange >= 1

Example (HDevelop)

read_image(Fabrik, 'fabrik')
reduce_domain(Fabrik, Rectangle_Label, Fabrik_Label)
* Character extraction without gray value expansion:
MaskSize := 31
mean_image(Fabrik_Label,Label_Mean_normal,MaskSize, MaskSize)
* The characters in the border region are not extracted !
* Character extraction with gray value expansion:
get_domain (Fabrik_Label, Domain)
expand_domain_gray (Fabrik_Label, Expanded_Fabrik_Label, MaskSize)
get_domain (Expanded_Fabrik_Label, Expanded_Domain)
shape_trans (Expanded_Domain, RegionRect, 'rectangle1')
difference (RegionRect, Expanded_Domain, Region_Difference)
overpaint_region (Expanded_Fabrik_Label, Region_Difference, 0, 'fill')
reduce_domain (Expanded_Fabrik_Label, Domain, Reduced_Expanded_Fabrik_Label)
mean_image (Reduced_Expanded_Fabrik_Label, Label_Mean_Expanded,\
MaskSize, MaskSize)


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


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

Possible Predecessors


Possible Successors

reduce_domainreduce_domainReduceDomainReduceDomainReduceDomain, mean_imagemean_imageMeanImageMeanImageMeanImage, dyn_thresholddyn_thresholdDynThresholdDynThresholdDynThreshold

See also

reduce_domainreduce_domainReduceDomainReduceDomainReduceDomain, mean_imagemean_imageMeanImageMeanImageMeanImage