Bottom-hat

Perform morphological bottom-hat filtering on intensity or binary images

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Libraries:
Computer Vision Toolbox / Morphological Operations

Description

The Bottom-hat block performs bottom-hat filtering on an intensity or binary image using a predefined neighborhood or structuring element. Bottom-hat filtering is the equivalent of subtracting the input image from the result of performing a morphological closing operation on the input image.

To define the structuring element that the block applies to the image, use the Neighborhood or structuring element parameter. Specify this element by entering a vector or matrix of 1s and 0s or by using the strel function.

This block uses two-dimensional flat structuring elements only.

Examples

Perform Bottom-hat Filtering of Binary Image

Perform bottom-hat filtering on a binary image object.

• Open Script

Ports

Input

I — Input image

matrix

Specify an input image as a matrix of intensity values. This port is unnamed unless you set the Neighborhood or structuring element source parameter to Input port.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean | fixed point

Nhood — Neighborhood values

vector | matrix

Specify neighborhood values representing a structuring element as a vector or matrix of 1s and 0s or by using the strel function.

Dependencies

To enable this port, set the Neighborhood or structuring element source parameter to Input port.

Data Types: Boolean

Output

Port_1 — Filtered image

matrix

The bottom-hat filtered image is returned as a matrix of intensity values. The size and data type of the filtered image are the same as those of the input image.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean | fixed point

Parameters

Input image type — Type of input image

Intensity (default) | Binary

Specify the type of image as one of these options:

• Intensity — If the input image is an intensity image, select this option.

• Binary — If the input image is a binary image, select this option.

Neighborhood or structuring element source — Source of neighborhood or structuring element

Specify via dialog (default) | Input port

Specify the source of neighborhood or structuring element as one of these options:

• Specify via dialog — Use the Neighborhood or structuring element parameter to specify a neighborhood or structuring element.

• Input port — Use the Nhood input port to specify neighborhood values representing a structuring element.

Neighborhood or structuring element — Neighborhood or structuring element

strel('octagon',15) (default) | vector | matrix

Specify neighborhood or structuring element as a vector or matrix of 1s and 0s, a strel object or an array of strel objects. When you specify this value as an array of strel objects, the block applies each object to the entire image in turn.

If the structuring element is decomposable into smaller elements, the block executes at higher speed due to the use of a more efficient algorithm.

Dependencies

To enable this parameter, set the Neighborhood or structuring element source parameter, to Specify via dialog.

Block Characteristics

Data Types	Boolean | double | fixed point | integer | single
Multidimensional Signals	no
Variable-Size Signals	yes

More About

Bottom-hat Transform

Image processing tasks like background equalization, feature extraction, and image enhancement can be achieved using the bottom-hat transform. This process returns an image which contains objects that are:

• Smaller in dimension than the structuring element chosen and

• Darker than the surroundings

References

[1] Soille, Pierre. Morphological Image Analysis. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. https://doi.org/10.1007/978-3-662-05088-0.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a