# Laplacian node¶

*This documentation is for version 4.0 of Laplacian.*

## Description¶

Blur input stream, and subtract the result from the input image. This is not a mathematically correct Laplacian (which would be the sum of second derivatives over X and Y).

Uses the ‘vanvliet’ and ‘deriche’ functions from the CImg library.

CImg is a free, open-source library distributed under the CeCILL-C (close to the GNU LGPL) or CeCILL (compatible with the GNU GPL) licenses. It can be used in commercial applications (see http://cimg.eu).

## Inputs¶

Input | Description | Optional |
---|---|---|

Source | No | |

Mask | Yes |

## Controls¶

Parameter / script name | Type | Default | Function |
---|---|---|---|

Size / `size` |
Double | x: 3 y: 3 | Size (diameter) of the filter kernel, in pixel units (>=0). The standard deviation of the corresponding Gaussian is size/2.4. No filter is applied if size < 1.2. |

Uniform / `uniform` |
Boolean | Off | Apply the same amount of blur on X and Y. |

Filter / `filter` |
Choice | Gaussian | Bluring filter. The quasi-Gaussian filter should be appropriate in most cases. The Gaussian filter is more isotropic (its impulse response has rotational symmetry), but slower.
Quasi-Gaussian (quasigaussian): Quasi-Gaussian filter (0-order recursive Deriche filter, faster) - IIR (infinite support / impulsional response).Gaussian (gaussian): Gaussian filter (Van Vliet recursive Gaussian filter, more isotropic, slower) - IIR (infinite support / impulsional response).Box (box): Box filter - FIR (finite support / impulsional response).Triangle (triangle): Triangle/tent filter - FIR (finite support / impulsional response).Quadratic (quadratic): Quadratic filter - FIR (finite support / impulsional response). |

(Un)premult / `premult` |
Boolean | Off | Divide the image by the alpha channel before processing, and re-multiply it afterwards. Use if the input images are premultiplied. |

Invert Mask / `maskInvert` |
Boolean | Off | When checked, the effect is fully applied where the mask is 0. |

Mix / `mix` |
Double | 1 | Mix factor between the original and the transformed image. |