Autothreshold

Convert intensity image to binary image

• Library:

• Computer Vision Toolbox / Conversions

• 

Description

The Autothreshold block converts an intensity image to a binary image using a threshold value. This block uses Otsu's method to determine the threshold.

Ports

Input

I — Input image

matrix

Input image, specified as an M-by-N matrix.

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

Output

BW — Output binary image

matrix

Output binary image, returned as an M-by-N matrix.

Data Types: Boolean

Th — Threshold value

scalar

Threshold value used to convert the intensity image to a binary image, returned as a scalar.

The block calculates the threshold value using Otsu's method. The block computes this value by splitting the histogram of the input image such that the variance of each pixel group is minimized.

Dependencies

To enable this port, select the Output threshold parameter.

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

EMetric — Effectiveness metric value

scalar

Effectiveness metric value, returned as a scalar in the range [0, 1].

If all the pixel values of the input image are the same, the value of the effectiveness metric is 0. If the image has two unique pixels, or if the histogram of the image is symmetric, the value of the effectiveness metric is 1.

Dependencies

To enable this port, select the Output effectiveness metric parameter.

Data Types: single | double

Parameters

Main

Thresholding operator — Specify thresholding operator

> (default) | <=

Select whether the block includes pixels from the intensity image with values below the threshold or those with values equal to or greater than the threshold in the output binary image.

• > — For pixel values of the input image greater than the threshold, the block outputs 1 in the binary image. Otherwise, the block assigns the pixel a value of 0.

• <= — For pixel values of the input image less than or equal to the threshold, the block outputs 1. Otherwise, the block assigns the pixel a value of 0.

Output threshold — Output threshold

off (default) | on

Select Output threshold to return the threshold value the block uses to convert the intensity image to a binary image. Selecting this parameter enables the Th output port.

Output effectiveness metric — Output effectiveness metric

off (default) | on

Select Output effectiveness metric to return the effectiveness metric value. Selecting this parameter enables the EMetric output port.

Specify data range — Specify input pixel value range

off (default) | on

Select Specify data range to enable specification of minimum and maximum input pixel values to use to determine the threshold. Selecting this parameter enables the Minimum value of input, Maximum value of input, and When data range is exceeded parameters.

Minimum value of input — Minimum input pixel value

0 (default) | scalar

Specify the minimum value of input pixels to use to determine the threshold.

Maximum value of input — Maximum input pixel value

255 (default) | scalar

Specify the maximum value of input pixels to use to determine the threshold.

When data range is exceeded — Operation to perform when data range is exceeded

Ignore (default) | Saturate | Warn and saturate | Error

Specify the behavior of the block when the value of an input image pixel exceeds the specified data range.

• Ignore — The block ignores all pixels with values outside the specified data range.

• Saturate — The block saturates the pixels with values below the data range to the specified minimum value, and those above the data range to the specified maximum value.

• Warn and saturate — The block displays a warning message in the MATLAB^® command window and saturates the pixel values as specified for the Saturate option.

• Error — The block displays an error message and ends the simulation.

Scale threshold — Specify scale threshold

off (default) | on

Select Scale threshold to enable specification of a scale factor for the thresholding operation. Selecting this parameter enables the Threshold scaling factor parameter.

Threshold scaling factor — Scale factor for thresholding

1 (default) | scalar

Specify the scaling factor for the thresholding operation as a scalar. The block performs thresholding by multiplying the threshold value computed by Otsu's method by the specified scale factor.

Data Types

For details on fixed-point block parameters, see Specify Fixed-Point Attributes for Blocks.

Lock data type settings against change by the fixed-point tools — Data type override

off (default) | on

Select this parameter to prevent the fixed-point tools from overriding the data types you specify in this block. For more information, see Lock the Output Data Type Setting (Fixed-Point Designer).

Model Examples

Convert Grayscale Image to Binary Image

Convert a grayscale image to a binary image using a global threshold.

Open Script

Block Characteristics

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

More About

Fixed-Point Data Types

This diagram shows the data types used in the Autothreshold block for fixed-point signals. You can use the default fixed-point parameters if your input has a word length less than or equal to 16.

In this diagram, DT means data type. You can set the product, accumulator, quotient, and effectiveness metric data types in the block mask.

Extended Capabilities

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

Version History

Introduced before R2006a