2-D FIR Filter
Perform 2-D FIR filtering on input matrix
Library
Filtering
visionfilter
Description
The 2-D Finite Impulse Response (FIR) filter block filters the input matrix
I
using the coefficient matrix H
or the
coefficient vectors HH
and HV
.
Port | Input/Output | Supported Data Types | Complex Values Supported |
---|---|---|---|
I | Vector or matrix of intensity values |
| Yes |
H | Matrix of filter coefficients | Same as I port. | Yes |
HH | Vector of filter coefficients | Same as I port. The input to ports HH and HV must be the same data type. | Yes |
HV | Vector of filter coefficients | Same as I port. The input to ports HH and HV must be the same data type. | Yes |
PVal | Scalar value that represents the constant pad value | Input must have the same data type as the input to I port. | Yes |
Output | Scalar, vector, or matrix of filtered values | Same as I port. | Yes |
If the input has a floating-point data type, then the output uses the same data type. Otherwise, the output can be any fixed-point data type.
Select the Separable filter coefficients check box if your filter
coefficients are separable. Using separable filter coefficients reduces the amount of
calculations the block must perform to compute the output. For example, suppose your
input image is M-by-N and your filter coefficient
matrix is x-by-y. For a nonseparable filter with the Output size
parameter set to Same as input port I
, it would take
multiply-accumulate (MAC) operations for the block to calculate the output. For a separable filter, it would only take
MAC operations. If you do not know whether or not your filter
coefficients are separable, use the isfilterseparable
function.
Here is an example of the function syntax, [S, HCOL, HROW] =
isfilterseparable(H)
. The isfilterseparable
function
takes the filter kernel, H
, and returns S
,
HCOL
and HROW
. Here, S
is a
Boolean variable that is 1 if the filter is separable and 0 if it is not.
HCOL
is a vector of vertical filter coefficients, and
HROW
is a vector of horizontal filter coefficients.
Use the Coefficient source parameter to specify how to define
your filter coefficients. If you select the Separable filter
coefficients check box and then select a Coefficient
source of Specify via dialog
, the
Vertical coefficients (across height) and Horizontal
coefficients (across width) parameters appear in the dialog box. You can
use these parameters to enter vectors of vertical and horizontal filter coefficients,
respectively.
You can also use the variables HCOL
and HROW
,
the output of the isfilterseparable
function, for these parameters.
If you select the Separable filter coefficients check box and then
select a Coefficient source of Input
port
, ports HV and HH appear on the block. Use these ports to specify
vectors of vertical and horizontal filter coefficients.
If you clear the Separable filter coefficients check box and
select a Coefficient source of Specify via
dialog
, the Coefficients parameter appears in the
dialog box. Use this parameter to enter your matrix of filter coefficients.
If you clear the Separable filter coefficients check box and
select a Coefficient source of Input
port
, port H appears on the block. Use this port
to specify your filter coefficient matrix.
The block outputs the result of the filtering operation at the Output port. The
Output size parameter and the sizes of the inputs at ports
I and H dictate the dimensions of the
output. For example, assume that the input at port I has dimensions
(Mi, Ni) and the input at port H has
dimensions (Mh, Nh). If you select an
Output size of Full
, the output has
dimensions (Mi+Mh-1,
Ni+Nh-1). If you select an Output
size of Same as input port I
, the output has
the same dimensions as the input at port I. If you select an Output
size of Valid
, the block filters the input
image only where the coefficient matrix fits entirely within it, so no padding is
required. The output has dimensions (Mi-Mh+1,
Ni-Nh+1).
However, if
all(size(I)<size(H))
, the block errors out.
Use the Padding options parameter to specify how to pad the
boundary of your input matrix. To pad your matrix with a constant value, select
Constant
. To pad your input matrix by repeating its
border values, select Replicate
. To pad your input matrix
with its mirror image, select Symmetric
. To pad your input
matrix using a circular repetition of its elements, select
Circular
. For more information on padding, see the Image Pad block reference page.
If, for the Padding options parameter, you select
Constant
, the Pad value source
parameter appears in the dialog box. If you select Specify via
dialog
, the Pad value parameter appears in the
dialog box. Use this parameter to enter the constant value with which to pad your
matrix. If you select Pad value source ofInput
port
, the PVal port appears on the block. Use this port to specify the
constant value with which to pad your matrix. The pad value must be real if the input
image is real. You will get an error message if the pad value is complex when the input
image is real.
Use the Filtering based on parameter to specify the algorithm by
which the block filters the input matrix. If you select
Convolution
and set the Output size
parameter to Full
, the block filters your input using the
following algorithm
where and . If you select Correlation
and set the
Output size parameter to Full
, the
block filters your input using the following algorithm
where and .
The imfilter
function from the Image Processing Toolbox™ product similarly performs N-D filtering of multidimensional
images.
Fixed-Point Data Types
The following diagram shows the data types used in the 2-D FIR Filter block for fixed-point signals.
You can set the coefficient, product output, accumulator, and output data types in the block mask as discussed in Parameters.
The output of the multiplier is in the product output data type if at least one of the inputs to the multiplier is real. If both of the inputs to the multiplier are complex, the result of the multiplication is in the accumulator data type. For details on the complex multiplication performed, refer to Multiplication Data Types.
Parameters
- Separable filter coefficients
Select this check box if your filter coefficients are separable. Using separable filter coefficients reduces the amount of calculations the block must perform to compute the output.
- Coefficient source
Specify how to define your filter coefficients. Select
Specify via dialog
to enter your coefficients in the block parameters dialog box. SelectInput port
to specify your filter coefficient matrix using port H or ports HH and HV.- Coefficients
Enter your real or complex-valued filter coefficient matrix. This parameter appears if you clear the Separable filter coefficients check box and then select a Coefficient source of
Specify via dialog
. Tunable.- Vertical coefficients (across height)
Enter the vector of vertical filter coefficients for your separable filter. This parameter appears if you select the Separable filter coefficients check box and then select a Coefficient source of
Specify via dialog
.- Horizontal coefficients (across width)
Enter the vector of horizontal filter coefficients for your separable filter. This parameter appears if you select the Separable filter coefficients check box and then select a Coefficient source of
Specify via dialog
.- Output size
This parameter controls the size of the filtered output. If you choose
Full
, the output has dimensions (Ma+Mh-1, Na+Nh-1). If you chooseSame as input port I
, the output has the same dimensions as the input at port I If you chooseValid
, output has dimensions (Ma-Mh+1, Na-Nh+1).- Padding options
Specify how to pad the boundary of your input matrix. Select
Constant
to pad your matrix with a constant value. SelectReplicate
to pad your input matrix by repeating its border values. SelectSymmetric
to pad your input matrix with its mirror image. SelectCircular
to pad your input matrix using a circular repetition of its elements. This parameter appears if you select an Output size ofFull
orSame as input port I
.- Pad value source
Use this parameter to specify how to define your constant boundary value. Select
Specify via dialog
to enter your value in the block parameters dialog box. SelectInput port
to specify your constant value using the PVal port. This parameter appears if you select a Padding options ofConstant
.- Pad value
Enter the constant value with which to pad your matrix. This parameter is visible if, for the Pad value source parameter, you select
Specify via dialog
. Tunable. The pad value must be real if the input image is real. You will get an error message if the pad value is complex when the input image is real.- Filtering based on
Specify the algorithm by which the block filters the input matrix. You can select
Convolution
orCorrelation
.- Rounding mode
Select the Rounding Modes for fixed-point operations.
- Saturate on integer overflow
Select the overflow mode for fixed-point operations. See Precision and Range.
- Coefficients
Choose how to specify the word length and the fraction length of the filter coefficients.
When you select
Inherit: Same word length as input
, the word length of the filter coefficients match that of the input to the block. In this mode, the block automatically sets the fraction length of the coefficients to the binary-point only scaling that provides you with the best precision possible given the value and word length of the coefficients.When you select
fixdt(1,16)
, you can enter the word length of the coefficients, in bits. In this mode, the block automatically sets the fraction length of the coefficients to the binary-point only scaling that provides you with the best precision possible given the value and word length of the coefficients.When you select
fixdt(1,16,0)
, you can enter the word length and the fraction length of the coefficients, in bits.When you select
<data type expression>
, you can enter the data type expression.
The filter coefficients do not obey the Rounding mode and the Saturate on integer overflow parameters; instead, they are always saturated and rounded to
Nearest
.Click the Show data type assistant button
to display the Data Type Assistant, which helps you set the Product output data type parameter.
See Specify Data Types Using Data Type Assistant (Simulink) for more information.
- Product output
Use this parameter to specify how to designate the product output word and fraction lengths. Refer to Fixed-Point Data Types and Multiplication Data Types for illustrations depicting the use of the product output data type in this block:
When you select
Inherit: Same as input
, these characteristics match those of the input to the block.When you select
fixdt([],16,0)
, you can enter the word length and the fraction length of the product output, in bits.When you select
<data type expression>
, you can enter the data type expression.
If you set the Coefficient source (on the Main tab) to
Input port
the Product Output will inherit its sign according to the inputs. If either or both input I1 and I2 are signed, the Product Output will be signed. Otherwise, the Product Output is unsigned. The following table shows all cases.Sign of Input I1 Sign of Input I2 Sign of Product Output unsigned unsigned unsigned unsigned signed signed signed unsigned signed signed signed signed Click the Show data type assistant button
to display the Data Type Assistant, which helps you set the Product output data type parameter.
See Specify Data Types Using Data Type Assistant (Simulink) for more information.
- Accumulator
Use this parameter to specify how to designate the accumulator word and fraction lengths. Refer to Fixed-Point Data Types and Multiplication Data Types for illustrations depicting the use of the accumulator data type in this block. The accumulator data type is only used when both inputs to the multiplier are complex:
When you select
Inherit: Same as input
, these characteristics match those of the input to the block.When you select
Inherit: Same as product output
, these characteristics match those of the product output.When you select
fixdt([],16,0)
, you can enter the word length and the fraction length of the accumulator, in bits.When you select
Slope and bias scaling
, you can enter the word length, in bits, and the slope of the accumulator. All signals in the Computer Vision Toolbox™ software have a bias of 0.
Click the Show data type assistant button
to display the Data Type Assistant, which helps you set the Product output data type parameter.
See Specify Data Types Using Data Type Assistant (Simulink) for more information.
- Output
Choose how to specify the word length and fraction length of the output of the block:
When you select
Inherit: Same as input
, these characteristics match those of the input to the block.When you select
fixdt([],16,0)
, you can enter the word length and the fraction length of the output, in bits.You can choose to set signedness of the output to
Auto
,Signed
orUnsigned
.When you select
<data type expression>
, you can enter the a data type expression.
Click the Show data type assistant button
to display the Data Type Assistant, which helps you set the Product output data type parameter.
See Specify Data Types Using Data Type Assistant (Simulink) for more information.
- Lock data type settings against change by the fixed-point tools
Select this parameter to prevent the fixed-point tools from overriding the data types you specify on the block mask. For more information, see
fxptdlg
(Fixed-Point Designer), a reference page on the Fixed-Point Tool in the Simulink® documentation.
See Also
Image Processing Toolbox |
Extended Capabilities
Version History
Introduced before R2006a