# filterDog2d

## PURPOSE

Difference of Gaussian (Dog) Filter.

## SYNOPSIS

function G = filterDog2d( r, var, order, show )

## DESCRIPTION

     Difference of Gaussian (Dog) Filter.

     Adapted from code by Serge Belongie.  Takes a "Difference of Gaussian" -
     all centered on the same point but with different values for sigma. Also
     serves as an approximation to an Laplacian of Gaussian (LoG) filter (if
     order==1).

     USAGE
      G = filterDog2d( r, var, order, [show] )

     INPUTS
      r       - Final filter will be 2*r+1 on each side
      var     - variance of central Gaussian
      order   - should be either 1-LoG or 2-difference of 3 Gaussians
      show    - [0] figure to use for optional display

     OUTPUTS
      G       - filter

     EXAMPLE
      G = filterDog2d( 40, 40, 1, 1 ); %order=1 (LoG)
      G = filterDog2d( 40, 40, 2, 3 ); %order=2

     See also FILTERDOOG, FILTERGAUSS

     Piotr's Image&Video Toolbox      Version 2.0
     Copyright 2008 Piotr Dollar.  [pdollar-at-caltech.edu]
     Please email me if you find bugs, or have suggestions or questions!
     Licensed under the Lesser GPL [see external/lgpl.txt]

## CROSS-REFERENCE INFORMATION

This function calls:

- filterGauss n-dimensional Gaussian filter.
- filterVisualize Used to visualize a 1D/2D/3D filter.
- c clc - clear command window.

This function is called by:

- FbMake Various 1D/2D/3D filterbanks (hardcoded).