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# makelut

Create lookup table for use with `bwlookup`

## Syntax

``lut = makelut(fun,n)``

## Description

example

````lut = makelut(fun,n)` creates a lookup table. `fun` is a function that creates a numeric output from a 2-by-2 or 3-by-3 binary neighborhood, where `n` determines the neighborhood size. `makelut` creates a lookup table by passing all possible neighborhoods to `fun`, one at a time, and storing the outputs in vector `lut`.Use the lookup table with `bwlookup` to perform nonlinear neighborhood filtering.```

## Examples

### Make Lookup Table for 2-by-2 Neighborhood

Construct a lookup table for 2-by-2 neighborhoods. In this example, the function passed to `makelut` returns `TRUE` if the number of `1`s in the neighborhood is 2 or greater, and returns `FALSE` otherwise.

```f = @(x) (sum(x(:)) >= 2); lut = makelut(f,2)```
```lut = 0 0 0 1 0 1 1 1 0 1 1 1 1 1 1 1```

## Input Arguments

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Function handle, specified as a handle. The function must accept an `n`-by-`n` binary matrix of `1`s and `0`s as input and return a scalar.

For more information about function handles, see Create Function Handle (MATLAB).

Neighborhood size for the lookup table, specified as `2` or `3`.

## Output Arguments

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Lookup table, returned as a 16-element numeric vector when `n` is `2`, or a 512-element numeric vector when `n` is `3`.

Data Types: `double`

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