rank_imagerank_imageRankImageRankImagerank_image (Operator)

Name

rank_imagerank_imageRankImageRankImagerank_image — Compute a rank filter with arbitrary masks.

Signature

Description

rank_imagerank_imageRankImageRankImagerank_image performs a rank filter on the input image ImageImageImageimageimage with a mask that is specified by the region MaskMaskMaskmaskmask and returns the filtered image in ImageRankImageRankImageRankimageRankimage_rank. The shape of the mask can be chosen arbitrarily and can, for example, be created with operators like gen_circlegen_circleGenCircleGenCirclegen_circle or draw_regiondraw_regionDrawRegionDrawRegiondraw_region. The position of the mask does not influence the result since the center of gravity of the mask region is used as the reference point of the mask.

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 A corresponds to the largest gray value within the mask. Here, A denotes the area of MaskMaskMaskmaskmask (see area_centerarea_centerAreaCenterAreaCenterarea_center). For RankRankRankrankrank = (A - 1) / 2 + 1, rank_imagerank_imageRankImageRankImagerank_image returns the median gray value (see median_imagemedian_imageMedianImageMedianImagemedian_image). For RankRankRankrankrank = 1, rank_imagerank_imageRankImageRankImagerank_image performs a gray value erosion (see gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectgray_erosion_rect, gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapegray_erosion_shape, and gray_erosiongray_erosionGrayErosionGrayErosiongray_erosion), while for RankRankRankrankrank = A rank_imagerank_imageRankImageRankImagerank_image performs a gray value dilation (see gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectgray_dilation_rect, gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapegray_dilation_shape, and gray_dilationgray_dilationGrayDilationGrayDilationgray_dilation).

rank_imagerank_imageRankImageRankImagerank_image can be used, for example, to suppress noise or to suppress unwanted objects that are smaller than the mask. Furthermore, rank_imagerank_imageRankImageRankImagerank_image 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 A, slightly larger or smaller values should be selected for RankRankRankrankrank.

Several border treatments can be chosen for filtering via the parameter MarginMarginMarginmarginmargin:

gray value

Pixels outside of the image border are assumed to be constant (with the indicated gray value).

'continued'"continued""continued""continued""continued"

Continuation of the gray values at the image border.

'cyclic'"cyclic""cyclic""cyclic""cyclic"

Cyclic continuation at the image borders.

'mirrored'"mirrored""mirrored""mirrored""mirrored"

Reflection of pixels at the image borders.

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

Attention

rank_imagerank_imageRankImageRankImagerank_image uses an algorithm with a runtime per pixel that depends on the number of runs in the mask MaskMaskMaskmaskmask. Therefore, rank_imagerank_imageRankImageRankImagerank_image is slower than rank_rectrank_rectRankRectRankRectrank_rect for rectangular masks with a large mask height. The precise mask height for which rank_rectrank_rectRankRectRankRectrank_rect will become faster than rank_imagerank_imageRankImageRankImagerank_image depends on the computer architecture (processor type, availability of SIMD instructions like SSE2 or MMX, cache size and throughput, memory throughput). Typically, this is the case for mask heights > 15, but can also be the case only for larger mask sizes, e.g., if SIMD instructions are unavailable and memory throughput is low.

Furthermore, it should be noted that rank_rectrank_rectRankRectRankRectrank_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_imageRankImageRankImagerank_image is faster than rank_rectrank_rectRankRectRankRectrank_rect even for larger mask heights.

rank_imagerank_imageRankImageRankImagerank_image should neither be used with RankRankRankrankrank = 1 to perform a gray value erosion nor with RankRankRankrankrank = A to perform a gray value dilation. In these cases, the operators gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectgray_erosion_rect, gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapegray_erosion_shape, or gray_erosiongray_erosionGrayErosionGrayErosiongray_erosion and gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectgray_dilation_rect, gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapegray_dilation_shape, or gray_dilationgray_dilationGrayDilationGrayDilationgray_dilation, respectively, are typically faster than rank_imagerank_imageRankImageRankImagerank_image.

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

Example (HDevelop)

read_image (Image, 'fabrik')
draw_region (Region, WindowHandle)
rank_image (Image, Region, ImageRank, 5, 'mirrored')
dev_display(ImageRank)

Complexity

For each pixel: O(N), where N is the number of runs of MaskMaskMaskmaskmask (see runlength_featuresrunlength_featuresRunlengthFeaturesRunlengthFeaturesrunlength_features).

Result

If the parameter values are correct the operator rank_imagerank_imageRankImageRankImagerank_image returns the value 2 ( H_MSG_TRUE) . The behavior in case of empty input (no input images available) is set via the operator set_system('no_object_result',<Result>)set_system("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_imageReadImageReadImageread_image, draw_regiondraw_regionDrawRegionDrawRegiondraw_region, gen_circlegen_circleGenCircleGenCirclegen_circle, gen_rectangle1gen_rectangle1GenRectangle1GenRectangle1gen_rectangle1, gen_rectangle2gen_rectangle2GenRectangle2GenRectangle2gen_rectangle2

Possible Successors

thresholdthresholdThresholdThresholdthreshold, dyn_thresholddyn_thresholdDynThresholdDynThresholddyn_threshold, regiongrowingregiongrowingRegiongrowingRegiongrowingregiongrowing

Alternatives

rank_rectrank_rectRankRectRankRectrank_rect, median_imagemedian_imageMedianImageMedianImagemedian_image, median_rectmedian_rectMedianRectMedianRectmedian_rect

See also

gray_erosion_rectgray_erosion_rectGrayErosionRectGrayErosionRectgray_erosion_rect, gray_dilation_rectgray_dilation_rectGrayDilationRectGrayDilationRectgray_dilation_rect, gray_erosion_shapegray_erosion_shapeGrayErosionShapeGrayErosionShapegray_erosion_shape, gray_dilation_shapegray_dilation_shapeGrayDilationShapeGrayDilationShapegray_dilation_shape, gray_erosiongray_erosionGrayErosionGrayErosiongray_erosion, gray_dilationgray_dilationGrayDilationGrayDilationgray_dilation

References

T.S. Huang, G.J. Yang, G.Y. Tang; “A Fast Two-Dimensional Median Filtering Algorithm”; IEEE Transactions on Acoustics, Speech, and Signal Processing, vol. 27, no. 1, pp. 13-18, 1979.
R. Haralick, L. Shapiro; “Computer and Robot Vision”; Addison-Wesley, 1992, pp. 318-320.

Module

Foundation