ClassesClasses | | Operators

rank_rectrank_rectRankRectRankRect (Operator)


rank_rectrank_rectRankRectRankRect — Compute a rank filter with rectangular masks.


rank_rect(Image : ImageRank : MaskWidth, MaskHeight, Rank : )

Herror rank_rect(const Hobject Image, Hobject* ImageRank, const Hlong MaskWidth, const Hlong MaskHeight, const Hlong Rank)

Herror T_rank_rect(const Hobject Image, Hobject* ImageRank, const Htuple MaskWidth, const Htuple MaskHeight, const Htuple Rank)

void RankRect(const HObject& Image, HObject* ImageRank, const HTuple& MaskWidth, const HTuple& MaskHeight, const HTuple& Rank)

HImage HImage::RankRect(Hlong MaskWidth, Hlong MaskHeight, Hlong Rank) const

static void HOperatorSet.RankRect(HObject image, out HObject imageRank, HTuple maskWidth, HTuple maskHeight, HTuple rank)

HImage HImage.RankRect(int maskWidth, int maskHeight, int rank)


rank_rectrank_rectRankRectRankRectRankRect performs a rank filter on the input image ImageImageImageImageimage with a rectangular mask of size MaskWidthMaskWidthMaskWidthMaskWidthmaskWidth × MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight and returns the filtered image in ImageRankImageRankImageRankImageRankimageRank.

Conceptually, the rank filter sorts all gray values within the mask in ascending order and then selects the gray value with rank RankRankRankRankrank. The rank 1 corresponds to the smallest gray value and the rank MaskWidthMaskWidthMaskWidthMaskWidthmaskWidth * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight corresponds to the largest gray value within the mask. For RankRankRankRankrank = (MaskWidthMaskWidthMaskWidthMaskWidthmaskWidth * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight - 1) / 2 + 1, rank_rectrank_rectRankRectRankRectRankRect returns the median gray value (see median_rectmedian_rectMedianRectMedianRectMedianRect). For RankRankRankRankrank = 1, rank_rectrank_rectRankRectRankRectRankRect performs a gray value erosion (see gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectGrayErosionRect, gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapeGrayErosionShape, and gray_erosiongray_erosionGrayErosionGrayErosionGrayErosion), while for RankRankRankRankrank = MaskWidthMaskWidthMaskWidthMaskWidthmaskWidth * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight rank_rectrank_rectRankRectRankRectRankRect performs a gray value dilation (see gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectGrayDilationRect, gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapeGrayDilationShape, and gray_dilationgray_dilationGrayDilationGrayDilationGrayDilation).

rank_rectrank_rectRankRectRankRectRankRect can be used, for example, to suppress noise or to suppress unwanted objects that are smaller than the mask. Furthermore, rank_rectrank_rectRankRectRankRectRankRect is less sensitive to noise than the correponding gray value morphology operators. Therefore, to obtain a more robust version of the gray value morphology, instead of using 1 or MaskWidthMaskWidthMaskWidthMaskWidthmaskWidth * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight, slightly larger or smaller values should be selected for RankRankRankRankrank.

For an explanation of the concept of smoothing filters see the introduction of chapter Filters / Smoothing.


If even values instead of odd values are passed in MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight or MaskWidthMaskWidthMaskWidthMaskWidthmaskWidth, rank_rectrank_rectRankRectRankRectRankRect uses the next larger odd values instead.

rank_rectrank_rectRankRectRankRectRankRect uses an algorithm with constant runtime per pixel, i.e., the runtime only depends on the size of the input image and not on the mask size. Therefore, for large mask sizes rank_rectrank_rectRankRectRankRectRankRect is the fastest implementation of the rank filter in HALCON. Depending on the computer architecture (processor type, availability of SIMD instructions like SSE2 or MMX, cache size and throughput, memory throughput), for small mask sizes the implementation used in rank_imagerank_imageRankImageRankImageRankImage is faster than rank_rectrank_rectRankRectRankRectRankRect. Typically, this is the case for MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight 15, but can also happen for larger mask sizes, e.g., if SIMD instructions are unavailable and memory throughput is low.

Furthermore, it should be noted that rank_rectrank_rectRankRectRankRectRankRect uses a recursive implementation, which internally computes the filter response on the smallest enclosing rectangle of the domain of the input image. Therefore, if the domain of the input image only covers a small fraction of the smallest enclosing rectangle, it can happen that rank_imagerank_imageRankImageRankImageRankImage is faster than rank_rectrank_rectRankRectRankRectRankRect even for larger values of MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight.

rank_rectrank_rectRankRectRankRectRankRect should neither be used with RankRankRankRankrank = 1 to perform a gray value erosion nor with RankRankRankRankrank = MaskWidthMaskWidthMaskWidthMaskWidthmaskWidth * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeight to perform a gray value dilation. In these cases, the operators gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectGrayErosionRect or gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapeGrayErosionShape and gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectGrayDilationRect or gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapeGrayDilationShape, respectively, are faster than rank_rectrank_rectRankRectRankRectRankRect for almost all mask sizes.

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


ImageImageImageImageimage (input_object)  (multichannel-)image(-array) objectHImageHImageHobject (byte)

Image to be filtered.

ImageRankImageRankImageRankImageRankimageRank (output_object)  (multichannel-)image(-array) objectHImageHImageHobject * (byte)

Filtered image.

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

Width of the filter mask.

Default value: 15

Suggested values: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 31, 49, 51, 61, 71, 81, 91, 101

Typical range of values: 3 ≤ MaskWidth MaskWidth MaskWidth MaskWidth maskWidth ≤ 4095

Minimum increment: 2

Recommended increment: 2

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

Height of the filter mask.

Default value: 15

Suggested values: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 31, 49, 51, 61, 71, 81, 91, 101

Typical range of values: 3 ≤ MaskHeight MaskHeight MaskHeight MaskHeight maskHeight ≤ 4095

Minimum increment: 2

Recommended increment: 2

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

Rank of the output gray value.

Default value: 5

Suggested values: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 31, 49, 51, 61, 71, 81, 91, 101

Minimum increment: 1

Recommended increment: 2

Restriction: 1 <= Rank && Rank <= MaskWidth * MaskHeight


For each pixel: O(1).


If the parameter values are correct the operator rank_rectrank_rectRankRectRankRectRankRect returns the value 2 (H_MSG_TRUE). The behavior in case of empty input (no input images available) is set via set_system('no_object_result',<Result>)set_system("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>)SetSystem("no_object_result",<Result>). If necessary, an exception is raised.

Possible Predecessors


Possible Successors

thresholdthresholdThresholdThresholdThreshold, dyn_thresholddyn_thresholdDynThresholdDynThresholdDynThreshold, regiongrowingregiongrowingRegiongrowingRegiongrowingRegiongrowing


rank_imagerank_imageRankImageRankImageRankImage, median_rectmedian_rectMedianRectMedianRectMedianRect, median_imagemedian_imageMedianImageMedianImageMedianImage

See also

gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectGrayErosionRect, gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectGrayDilationRect, gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapeGrayErosionShape, gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapeGrayDilationShape, gray_erosiongray_erosionGrayErosionGrayErosionGrayErosion, gray_dilationgray_dilationGrayDilationGrayDilationGrayDilation


S. Perreault, P. Hébert; “Median Filtering in Constant Time”; IEEE Transactions on Image Processing, vol. 16, no. 9, pp. 2389-2394, 2007.
D. Cline, K.B. White, P.K. Egbert; “Fast 8-Bit Median Filtering Based On Separability”; International Conference on Image Processing, vol. V, pp. 281-284, 2007.



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