Compute standard deviation of input or sequence of inputs
Computer Vision Toolbox / Statistics
The 2D Standard Deviation block computes the standard deviation of an input array. The input can be a 1D vector, 2D matrix, or an NDarray. The block can compute standard deviation along a specified dimension of the input or the entire input. If you select the Running standard deviation parameter, the block can also track the standard deviation in a sequence of inputs over a time period.
In
— Input arrayInput array, specified as a vector, matrix, or ND array. This port is unnamed until you select the Enable ROI processing parameter.
Data Types: single
 double
Complex Number Support: Yes
Rst
— Reset portReset port, specified as a scalar. This port specifies the event that causes the block to reset the running standard deviation. The sample time of the Rst input must be a positive integer and a multiple of the input sample time.
To enable this port, select the Running standard deviation
parameter and set the Reset port parameter to
Rising edge
, Falling edge
,
Either edge
, or Nonzero
sample
.
Data Types: single
 double
 int8
 int16
 int32
 uint8
 uint16
 uint32
 Boolean
ROI
— Region of interestRegion of interest (ROI), specified as a fourelement vector, mby4 matrix, or MbyN matrix. The input value to this port depends on the ROI type parameter.
Note
You can use the ROI
port only if the input is a 2D
image.
To enable this port, set the Find the standard deviation value
over parameter to Entire input
and select
the Enable ROI processing parameter.
Data Types: single
 double
 int8
 int16
 int32
 uint8
 uint16
 uint32
 Boolean
 fixed point
Label
— Label matrixLabel matrix, specified as a matrix of nonnegative integers. The label matrix represents the objects in an image. The pixels labeled 0 are the background. The pixels labeled 1 make up one object; the pixels labeled 2 make up a second object; and so on. The size of the label matrix must be the same size as the 2D input.
To enable this port, select the Enable ROI processing
parameter and set the ROI type parameter to
Label matrix
.
Data Types: uint8
 uint16
 uint32
Label Numbers
— Label values of ROIsLabel values of ROIs, specified as a Melement vector. The value of M can be less than or equal to the number of objects that are labeled in the label matrix.
To enable this port, select the Enable ROI processing
parameter and set the ROI type parameter to
Label matrix
.
Data Types: uint8
 uint16
 uint32
Out
— Computed output standard deviationComputed output standard deviation, returned as a scalar, vector, matrix, or NDarray. The size of the returned output standard deviation depends on the size of the input, and the settings for the Running standard deviation and Find the standard deviation value over parameters.
This port is unnamed until you select the Output flag indicating if ROI
is within image bounds and the ROI type parameter is
set to Rectangles
, Lines
, or
Label matrix
.
You can compute standard deviation along any specified dimension of the input or the entire input. The output is a:
Scalar if the input is of any size and the Find the
standard deviation value over parameter is set to
Entire input
.
Vector if the input is a matrix and the Find the
standard deviation value over parameter is set to any one of
Each row
, Each column
,
and Specified dimension
. In this case, the
Dimension value for Specified
dimension
can be either 1 or 2.
Matrix if the input is a 3D array and the Find the
standard deviation value over parameter is set to
Specified dimension
and the
Dimension value is 3.
ND array if the input is an ND array
and the Find the standard deviation value over
parameter is set to an option other than Entire
input
.
If you compute standard deviation along the Nth dimension
of the input, then the returned output is an (N1)D array.
In this case, the Dimension value for
Specified dimension
is set to
N.
Example: For a 3D input array of size MbyNbyP, the dimension of the returned output is:
1byNbyP if you set the
Find the standard deviation value over
parameter to Entire row
.
Mby1byP if you set the
Find the standard deviation value over
parameter to Entire column
.
MbyN if you set the Find the standard deviation value over parameter
to Specified dimension
and the
Dimension value to 3.
When you select the Running standard deviation parameter, the block computes the standard deviation of each sample in the input with respect to all previous samples. The output is of the same size as the input.
Data Types: single
 double
 int8
 int16
 int32
 uint8
 uint16
 uint32
 fixed point
Flag
— Validation for ROIValidation for ROI, returned as 0 or 1. The output value signifies if all of the ROIs specified at the input lie within the image bounds. The output value depends on the values of the Output and ROI Type parameters.
ROI Type  Output  Output from Flag port  Description 
 Individual statistics for each
ROI  0  ROI is completely outside the input image. 
1  ROI is either completely or partially inside the input image.  
Single statistic for all
ROIs  0  ROI is completely outside the input image.  
1  ROI is either completely or partially inside the input image.  
Label matrix  Individual statistics for each
ROI  0  Label number is not in the label matrix. 
1  Label number is in the label matrix.  
Single statistic for all
ROIs  0  None of the label numbers are in the label matrix.  
1  At least one of the label numbers is in the label matrix. 
Note
If the ROI is partially outside the image, the block computes the standard deviation values only for the portion of the ROI that lies within the image bounds.
To enable this port, select the Output flag indicating if ROI is
within image bounds parameter and set the value of ROI
type parameter to Rectangle
,
Lines
, or Label
Matrix
.
Main Tab
Running standard deviation
— Track running standard deviationSelect to track the standard deviation of successive inputs to the block. In this mode, the block treats each element as a channel.
Reset port
— Reset eventNone
(default)  Rising edge
 Falling edge
 Either edge
 Nonzero sample
Specify when the block detects a reset event. The block resets the running standard deviation when a reset event is detected at the optional Rst port. The reset sample time must be a positive integer and a multiple of the input sample time.
Specify the reset event as:
None
to disable the Rst port.
Rising edge
to trigger a reset event when the
Rst input does one of the following:
Rises from a negative value to either a positive value or zero
Rises from zero to a positive value, where the rise is not a continuation of a rise from a negative value to zero
Falling edge
to trigger a reset event when the
Rst input does one of the following:
Falls from a positive value to either a negative value or zero
Falls from zero to a negative value, where the fall is not a continuation of a fall from a positive value to zero
Either edge
to trigger a reset event when
the Rst input is a Rising
edge
or Falling edge
.
Nonzero sample
to trigger a reset event at each
sample time, when the Rst input is not zero.
Note
When running simulations in the Simulink^{®} multitasking mode, reset signals have a onesample latency. Therefore, when the block detects a reset event, there is a onesample delay at the reset port rate before the block applies the reset.
To enable this parameter, select the Running standard deviation parameter.
Find the standard deviation value over
— Dimension along which standard deviation is computedEntire input
(default)  Each row
 Each column
 Specified dimension
Specify the dimension of the input along which the block computes the standard deviation.
Entire input
— Computes standard deviation
over the entire input.
Each row
— Computes standard deviation over
each row.
Each column
— Computes standard deviation
over each column.
Specified dimension
— Computes standard
deviation over the dimension specified in the Dimension
parameter. By default, the Dimension parameter is set
to 1 and the output is the same as when you select Each
column
.
To enable this parameter, clear the Running standard deviation parameter.
Dimension
— Custom dimensionSpecify the dimension of the input array over which the standard deviation is computed as a onebased value. The value of this parameter is set to 1..
To enable this parameter, set the Find the standard deviation value
over parameter to Specified dimension
.
ROI Processing
Enable ROI processing
— Compute standard deviation within a particular regionSelect to calculate standard deviation within a particular ROI in the image.
Note
Full ROI processing is available only if you have a Computer Vision Toolbox™ license. If you do not have a Computer Vision Toolbox license, you can still use ROI processing, but the ROI
type is limited to Rectangles
.
To enable this parameter, set the Find the standard deviation value
over parameter to Entire input
.
ROI type
— Type of ROI Rectangles
(default)  Lines
 Label matrix
 Binary mask
Specify the type of ROI that represents the regions in the image over which the block computes the standard deviation. The type of ROI can be a rectangle, line, label matrix, or a binary mask.
Parameters  Description  
ROI type  Inputs to the ROI port  
Rectangles 


Lines 


Label matrix  MbyN matrix  Matrix of the same size as the input image. The matrix contains label values that represent different objects in an image. The pixels labeled 0 are the background. The pixels labeled 1 make up one object; the pixels labeled 2 make up a second object; and so on. 
Binary mask  MbyN matrix  Matrix of the same size as the input image. The binary mask classifies image pixels as belonging to either the region of interest or the background. The mask pixel values of 1 indicate that the image pixel belongs to the ROI. The mask pixel values of 0 indicate that the image pixel is part of the background. 
To enable this parameter, select the Enable ROI processing parameter.
ROI portion to process
— Portion of ROI in which to calculate standard deviationEntire ROI
(default)  ROI perimeter
Specify the portion of the ROI from which the block has to calculate 2D standard deviation. The ROI portion is either the entire ROI or the ROI perimeter.
To enable this parameter, select the Enable ROI processing
parameter and set the ROI type parameter to
Rectangles
.
Output
— Calculate standard deviation for individual or entire ROIIndividual statistics for each
ROI
(default)  Single statistic for all ROIs
Specify whether to calculate 2D standard deviation individually for each ROI or for the entire ROI.
If you select Individual statistics for each ROI
,
the block outputs a vector of standard deviation values. The size of the output
vector is equal to the number of ROIs.
If you select Single statistic for all ROIs
, the
block outputs a scalar value. The scalar value represents the statistical value
for all the specified ROIs.
To enable this parameter, select the Enable ROI processing
parameter and set the ROI type parameter to
Rectangles
, Lines
, or
Label matrix
.
Output flag indicating if ROI is within image bounds
— Enable Flag portSelect to expose the Flag port. For a description of the Flag port output, see Flag.
To enable this parameter, select the Enable ROI processing
parameter and set the ROI type parameter to
Rectangles
, Lines
, or
Label matrix
.
Data Types Tab
For details on the fixedpoint block parameters, see Specify FixedPoint Attributes for Blocks.
Lock data type settings against change by the fixedpoint tools
— Prevent fixedpoint tools from overriding data typesSelect this parameter to prevent the fixedpoint tools from overriding the data types you specify in this block. For more information, see Lock the Output Data Type Setting (FixedPoint Designer).
Data Types 

Multidimensional Signals 

VariableSize Signals 

2D
Mean  2D
Variance  var
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