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# fsamp2

2-D FIR filter using frequency sampling

## Syntax

``h = fsamp2(Hd)``
``h = fsamp2(f1,f2,Hd,[m n])``

## Description

example

````h = fsamp2(Hd)` designs a two-dimensional FIR filter with frequency response `Hd`, and returns the filter coefficients in matrix `h`. The filter `h` has a frequency response that passes through points in `Hd`. `fsamp2` designs two-dimensional FIR filters based on a desired two-dimensional frequency response sampled at points on the Cartesian plane. ```
````h = fsamp2(f1,f2,Hd,[m n])` produces an `m`-by-`n` FIR filter by matching the filter response at the points in the vectors `f1` and `f2`. The frequency vectors `f1` and `f2` are in normalized frequency, where 1.0 corresponds to half the sampling frequency, or π radians. The resulting filter fits the desired response as closely as possible in the least squares sense. For best results, there must be at least `m*n` desired frequency points. `fsamp2` issues a warning if you specify fewer than `m*n` points.```

## Examples

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Use `fsamp2` to design an approximately symmetric, two-dimensional bandpass filter with passband between 0.1 and 0.5 (normalized frequency, where 1.0 corresponds to half the sampling frequency, or radians).

Create a matrix `Hd` that contains the desired bandpass response. Use `freqspace` to create the frequency vectors `f1` and `f2`.

```[f1,f2] = freqspace(21,'meshgrid'); Hd = ones(21); r = sqrt(f1.^2 + f2.^2); Hd((r<0.1)|(r>0.5)) = 0; colormap(jet(64)) mesh(f1,f2,Hd)```

Design the filter that passes through this response.

```h = fsamp2(Hd); freqz2(h)```

## Input Arguments

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Frequency response, specified as a numeric matrix. `Hd` is a matrix containing the desired frequency response sampled at equally spaced points between -1.0 and 1.0 along the x and y frequency axes. The value 1.0 corresponds to half the sampling frequency, or π radians.

`${H}_{d}\left({f}_{1},{f}_{2}\right)={{H}_{d}\left({\omega }_{1},{\omega }_{2}\right)|}_{{\omega }_{1}=\pi {f}_{1},{\omega }_{2}=\pi {f}_{1}}$`

For best results, use frequency points returned by `freqspace` to create `Hd`.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64`

Frequency vector, specified as a numeric vector.

Data Types: `double`

Frequency vector, specified as a numeric vector.

Data Types: `double`

## Output Arguments

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2-D FIR filter, returned as a numeric array of class `double`. `fsamp2` returns `h` as a computational molecule, which is the appropriate form to use with `filter2`. If `Hd` is of class `single`, `h` is also of class `single`. If `Hd` is `m`-by-`n`, then `h` is also `m`-by-`n`.

## Algorithms

`fsamp2` computes the filter `h` by taking the inverse discrete Fourier transform of the desired frequency response. If the desired frequency response is real and symmetric (zero phase), the resulting filter is also zero phase.

## References

[1] Lim, Jae S., Two-Dimensional Signal and Image Processing, Englewood Cliffs, NJ, Prentice Hall, 1990, pp. 213-217.