Erosion

Morphological erosion of binary pixel data

Library:
Vision HDL Toolbox / Morphological Operations

Description

The Erosion block replaces each pixel with the local minimum of the neighborhood around the pixel. The block operates on a stream of binary intensity values. You can specify a neighborhood or structuring element of up to 32-by-32 pixels.

This block uses a streaming pixel interface with a bus for frame control signals. This interface enables the block to operate independently of image size and format. The pixel ports on this block support single pixel streaming or multipixel streaming. Single pixel streaming accepts and returns a single pixel value each clock cycle. Multipixel streaming accepts and returns 4 or 8 pixels per clock cycle to support high-frame-rate or high-resolution formats. Along with the pixel, the block accepts and returns a pixelcontrol bus that contains five control signals. The control signals indicate the validity of each pixel and their location in the frame. For multipixel streaming, one set of control signals applies to all four or eight pixels in the vector. To convert a frame (pixel matrix) into a serial pixel stream and control signals, use the Frame To Pixels block. For a full description of the interface, see Streaming Pixel Interface.

Ports

Input

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`pixel` — Boolean input pixel or multipixel vector
scalar | vector

This block supports single pixel streaming or multipixel streaming. For single pixel streaming, specify a single input pixel as a scalar Boolean value. For multipixel streaming, specify a vector of four or eight Boolean values. For details of how to set up your model for multipixel streaming, see Filter Multipixel Video Streams.

Data Types: Boolean

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Specify a pixelcontrol bus that contains five signals. The signals describe the validity of the pixel and its location in the frame. For more information, see Pixel Control Bus.

For multipixel streaming, each vector of pixel values has one set of control signals. Because the vector has only one valid signal, the pixels in the vector must be either all valid or all invalid. The hStart and vStart signals apply to the pixel with the lowest index in the vector. The hEnd and vEnd signals apply to the pixel with the highest index in the vector.

Data Types: bus

Output

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`pixel` — Boolean output pixel or multipixel vector
scalar | vector

This block supports single pixel streaming or multipixel streaming. When using single pixel streaming, the block returns a single pixel as a scalar Boolean value. When using multipixel streaming, the block returns a vector of Boolean values. This vector is the same size as the input pixel vector. For details of how to set up your model for multipixel streaming, see Filter Multipixel Video Streams.

Data Types: Boolean

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Specify a pixelcontrol bus that contains five signals. The signals describe the validity of the pixel and its location in the frame. For more information, see Pixel Control Bus.

For multipixel streaming, each vector of pixel values has one set of control signals. Because the vector has only one valid signal, the pixels in the vector are either all valid or all invalid. The hStart and vStart signals apply to the pixel with the lowest index in the vector. The hEnd and vEnd signals apply to the pixel with the highest index in the vector.

Data Types: bus

Parameters

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`Neighborhood` — Pixel neighborhood
`ones(3,3)` (default) | vector or matrix of `1`s and `0`s

Pixel neighborhood, specified as a vector or matrix of 1s and 0s.

The block supports neighborhoods of up to 32-by-32 pixels. To use a structuring element, specify Neighborhood as getnhood (Image Processing Toolbox)(strel (Image Processing Toolbox)(shape)).

When you use multipixel vector input, the neighbourhood must be at least two pixels in each dimension.

`Line buffer size` — Size of line memory buffer
`2048` (default) | positive integer

Specify a power of two that accommodates the number of active pixels in a single horizontal line.

If you specify a value that is not a power of two, the block uses the next largest power of two. The block allocates (neighborhood lines – 1)-by-Line buffer size memory locations to store the pixels.

`Padding method` — Method for padding
`Constant` (default) | `None`

Select one of these methods for padding the boundary of the input image. For more information about these methods, see Edge Padding.

Constant — The block pads the image with ones. This value prevents erosion at the boundaries of the active frame.
None — Exclude padding logic. The block does not set the pixels outside the image frame to any particular value. This option reduces the hardware resources used by the block and the blanking required between frames but affects the accuracy of the output pixels at the edges of the frame. To maintain pixel stream timing, the output frame is the same size as the input frame. However, to avoid using pixels calculated from undefined padding values, mask off the KernelSize/2 pixels around the edge of the frame for downstream operations. For details, see Increase Throughput with Padding None.

Algorithms

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Latency

The latency of the block is the line buffer latency plus the latency of the kernel calculation. The line buffer latency includes edge padding by default. The latency of the padding operation depends on the size of the kernel. If edge padding is not necessary for your design, you can reduce the latency by setting the Padding method parameter to None. When you use this option, the block latency does not depend on your kernel size. To determine the exact latency for any configuration of the block, measure the number of time steps between the input and output control signals.

The latency of the kernel depends on the neighborhood size.

Note

When you use edge padding, use a horizontal blanking interval greater than twice the kernel width. This interval lets the block finish processing one line before it starts processing the next one, including adding padding pixels before and after the active pixels in the line. Standard streaming video formats use a horizontal blanking interval of about 25% of the frame width. This interval is much larger than the filters applied to each frame. When you disable edge padding, the horizontal blanking interval must be at least 12 cycles and is independent of the kernel size. If you are using a custom video format, set the horizontal blanking interval by using the Frame To Pixels block parameters. The horizontal blanking interval is equal to Total pixels per line – Active pixels per line or, equivalently, Front porch + Back porch. For more information, see Configure Blanking Intervals.

Extended Capabilities

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

This block supports C/C++ code generation for Simulink^® accelerator and rapid accelerator modes and for DPI component generation.

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

HDL Architecture

This block has a single, default HDL architecture.

HDL Block Properties

ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays within your design. Distributed pipelining does not redistribute these registers. The default is `0`. For more details, see ConstrainedOutputPipeline (HDL Coder).
InputPipeline	Number of input pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is `0`. For more details, see InputPipeline (HDL Coder).
OutputPipeline	Number of output pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is `0`. For more details, see OutputPipeline (HDL Coder).

Restrictions

You cannot generate HDL code for this block if it is inside a Resettable Synchronous Subsystem (HDL Coder).

Documentation

Erosion

Description

Ports

Input

`pixel` — Boolean input pixel or multipixel vector
scalar | vector

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Output

`pixel` — Boolean output pixel or multipixel vector
scalar | vector

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

Parameters

`Neighborhood` — Pixel neighborhood
`ones(3,3)` (default) | vector or matrix of `1`s and `0`s

`Line buffer size` — Size of line memory buffer
`2048` (default) | positive integer

`Padding method` — Method for padding
`Constant` (default) | `None`

Algorithms

Latency

Extended Capabilities

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

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

See Also

Topics

Vision HDL Toolbox Documentation

Support

Documentation

Erosion

Description

Ports

Input

pixel — Boolean input pixel or multipixel vector scalar | vector

ctrl — Control signals associated with pixel stream pixelcontrol bus

Output

pixel — Boolean output pixel or multipixel vector scalar | vector

ctrl — Control signals associated with pixel stream pixelcontrol bus

Parameters

Neighborhood — Pixel neighborhood ones(3,3) (default) | vector or matrix of 1s and 0s

Line buffer size — Size of line memory buffer 2048 (default) | positive integer

Padding method — Method for padding Constant (default) | None

Algorithms

Latency

Extended Capabilities

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

HDL Code Generation Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

See Also

Topics

Vision HDL Toolbox Documentation

Support

`pixel` — Boolean input pixel or multipixel vector
scalar | vector

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

`pixel` — Boolean output pixel or multipixel vector
scalar | vector

`ctrl` — Control signals associated with pixel stream
`pixelcontrol` bus

`Neighborhood` — Pixel neighborhood
`ones(3,3)` (default) | vector or matrix of `1`s and `0`s

`Line buffer size` — Size of line memory buffer
`2048` (default) | positive integer

`Padding method` — Method for padding
`Constant` (default) | `None`

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

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.