Operators

erosion_rectangle1 (Operator)

Name

erosion_rectangle1 — Erode a region with a rectangular structuring element.

Signature

erosion_rectangle1(Region : RegionErosion : Width, Height : )

Description

erosion_rectangle1 applies an erosion with a rectangular structuring element to the input regions Region. The size of the structuring rectangle is Width x Height. The operator results in reduced regions, and the areas smaller than the rectangular mask are eliminated.

erosion_rectangle1 is a very fast operation because the height of the rectangle enters only logarithmically into the runtime complexity, while the width does not enter at all. This leads to excellent runtime efficiency, even in the case of very large rectangles (edge length > 100).

Regions containing small connecting strips between large areas are separated only seemingly. They remain logically one region.

Attention

To reduce a region by the same amount in all directions, Width and Height must be odd. If this is not the case, the region is eroded by a larger amount at the right or at the bottom, respectively, than at the left or at the top.

Parallelization

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Automatically parallelized on tuple level.

Parameters

Region (input_object)  region(-array) object

Regions to be eroded.

RegionErosion (output_object)  region(-array) object

Eroded regions.

Width (input_control)  extent.x (integer)

Width of the structuring rectangle.

Default value: 11

Suggested values: 1, 2, 3, 4, 5, 11, 15, 21, 31, 51, 71, 101, 151, 201

Typical range of values: 1 ≤ Width ≤ 511 (lin)

Minimum increment: 1

Recommended increment: 1

Height (input_control)  extent.y (integer)

Height of the structuring rectangle.

Default value: 11

Suggested values: 1, 2, 3, 4, 5, 11, 15, 21, 31, 51, 71, 101, 151, 201

Typical range of values: 1 ≤ Height ≤ 511 (lin)

Minimum increment: 1

Recommended increment: 1

Complexity

Let F1 be the area of an input region and H be the height of the rectangle. Then the runtime complexity for one region is:

```       O(sqrt(F1) * ld(H)) .
```

Result

erosion_rectangle1 returns 2 (H_MSG_TRUE) if all parameters are correct. The behavior in case of empty or no input region can be set via:

• no region: set_system('no_object_result',<RegionResult>)

• empty region: empty region: set_system('empty_region_result',<RegionResult>)

Otherwise, an exception is raised.