rank_rectrank_rectRankRectRankRectrank_rect (Operator)

Name

rank_rectrank_rectRankRectRankRectrank_rect — Compute a rank filter with rectangular masks.

Signature

Description

rank_rectrank_rectRankRectRankRectRankRectrank_rect performs a rank filter on the input image ImageImageImageImageimageimage with a rectangular mask of size MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width × MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height and returns the filtered image in ImageRankImageRankImageRankImageRankimageRankimage_rank.

Conceptually, the rank filter sorts all gray values within the mask in ascending order and then selects the gray value with rank RankRankRankRankrankrank. The rank 1 corresponds to the smallest gray value and the rank MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height corresponds to the largest gray value within the mask. For RankRankRankRankrankrank = (MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height - 1) / 2 + 1, rank_rectrank_rectRankRectRankRectRankRectrank_rect returns the median gray value (see median_rectmedian_rectMedianRectMedianRectMedianRectmedian_rect). For RankRankRankRankrankrank = 1, rank_rectrank_rectRankRectRankRectRankRectrank_rect performs a gray value erosion (see gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectGrayErosionRectgray_erosion_rect, gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapeGrayErosionShapegray_erosion_shape, and gray_erosiongray_erosionGrayErosionGrayErosionGrayErosiongray_erosion), while for RankRankRankRankrankrank = MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height rank_rectrank_rectRankRectRankRectRankRectrank_rect performs a gray value dilation (see gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectGrayDilationRectgray_dilation_rect, gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapeGrayDilationShapegray_dilation_shape, and gray_dilationgray_dilationGrayDilationGrayDilationGrayDilationgray_dilation).

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

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

Attention

If even values instead of odd values are passed in MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height or MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width, rank_rectrank_rectRankRectRankRectRankRectrank_rect uses the next larger odd values instead.

rank_rectrank_rectRankRectRankRectRankRectrank_rect 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_rectRankRectRankRectRankRectrank_rect 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_imageRankImageRankImageRankImagerank_image is faster than rank_rectrank_rectRankRectRankRectRankRectrank_rect. Typically, this is the case for MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height 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_rectRankRectRankRectRankRectrank_rect 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_imageRankImageRankImageRankImagerank_image is faster than rank_rectrank_rectRankRectRankRectRankRectrank_rect even for larger values of MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height.

rank_rectrank_rectRankRectRankRectRankRectrank_rect should neither be used with RankRankRankRankrankrank = 1 to perform a gray value erosion nor with RankRankRankRankrankrank = MaskWidthMaskWidthMaskWidthMaskWidthmaskWidthmask_width * MaskHeightMaskHeightMaskHeightMaskHeightmaskHeightmask_height to perform a gray value dilation. In these cases, the operators gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectGrayErosionRectgray_erosion_rect or gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapeGrayErosionShapegray_erosion_shape and gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectGrayDilationRectgray_dilation_rect or gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapeGrayDilationShapegray_dilation_shape, respectively, are faster than rank_rectrank_rectRankRectRankRectRankRectrank_rect 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

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

Parameters

Complexity

For each pixel: O(1).

Result

If the parameter values are correct the operator rank_rectrank_rectRankRectRankRectRankRectrank_rect returns the value 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>)set_system("no_object_result",<Result>). If necessary, an exception is raised.

Possible Predecessors

read_imageread_imageReadImageReadImageReadImageread_image

Possible Successors

thresholdthresholdThresholdThresholdThresholdthreshold, dyn_thresholddyn_thresholdDynThresholdDynThresholdDynThresholddyn_threshold, regiongrowingregiongrowingRegiongrowingRegiongrowingRegiongrowingregiongrowing

Alternatives

rank_imagerank_imageRankImageRankImageRankImagerank_image, median_rectmedian_rectMedianRectMedianRectMedianRectmedian_rect, median_imagemedian_imageMedianImageMedianImageMedianImagemedian_image

See also

gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectGrayErosionRectgray_erosion_rect, gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectGrayDilationRectgray_dilation_rect, gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapeGrayErosionShapegray_erosion_shape, gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapeGrayDilationShapegray_dilation_shape, gray_erosiongray_erosionGrayErosionGrayErosionGrayErosiongray_erosion, gray_dilationgray_dilationGrayDilationGrayDilationGrayDilationgray_dilation

References

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.

Module

Foundation