DIPlib Documentation - ©1995-2009 Quantitative Imaging Group, Delft University of Technology.

# Convolve1d

Perform a 1D convolution

## SYNOPSIS

`#include "dip_linear.h"`

dip_Error DIP_TPI_FUNC(dip_Convolve1d)( in, out, filter, size, filterSize, origin, flags, boundary )

## DATA TYPES

integer,float

## FUNCTION

This function performs a one-dimensional convolution of the input data with the given filter kernel. In general your filter will be centered around the origin. The origin is uniquely defined if the filter size is odd, but if the filter size is even you'll have to specify whether the origin of the filter lies to the left or the right. Words cannot possibly suffice here, so here is a small pictorial representation:

    filter size is odd :             kernel data :     x x x x x
                                                           ^
                                                           0

    filter size is even and
       DIP_CNV_LEFT is specified :   kernel data :     x x x x x x
                                                           ^
                                                           0

       DIP_CNV_RIGHT is specified :  kernel data :     x x x x x x
                                                             ^
                                                             0

When the filter size is even, one of the flags `DIP_CNV_LEFT` or `DIP_CNV_RIGHT` must be specified. When the filter size is odd both flags are ignored. It is also possible to specify the origin of the filter directly by using the `DIP_CNV_USE_ORIGIN` flag in combination with the `origin` parameter. Again a small pictorial representation:

                      0 1 2 3 4 5 6 7 8
    kernel data :     x x x x x x x x x     when origin = 2
                          ^
                          0

when DIP_CNV_USE_ORIGIN is NOT specified origin is computed as follows :

    filter size odd      origin = ( filterSize - 1 ) / 2
    filter size even _and_
       DIP_CNV_LEFT      origin = ( filterSize / 2 ) - 1
       DIP_CNV_RIGHT     origin = filterSize / 2

The input data is copied to a temporary buffer, after which the input data is extended according to the boundary condition specified. You can use the flags `DIP_CNV_HAS_BORDER` to indicate that the input data already has a border. In this case you must make sure that there are enough pixels on either size of the array:

       on the left  :  ( ( filterSize - 1 ) - origin )  pixels
       on the right :  ( origin )  pixels

If `DIP_CNV_HAS_BORDER` is specified and `in` != `out` no auxiliary storage is used. You must also specify the symmetry of the filter as follows:

       odd filter size    :   a  b  c  b  a      DIP_CNV_EVEN
                              a  b  c -b -a      DIP_CNV_ODD
                              a  b  c  d  e      DIP_CNV_GENERAL

       even filter size   :   a  b  c  c  b  a   DIP_CNV_EVEN
                              a  b  c -c -b -a   DIP_CNV_ODD
                              a  b  c  d  e  f   DIP_CNV_GENERAL

## ARGUMENTS

Data type | Name | Description
`void *` | `in` | Pointer to the input data
`void *` | `out` | Pointer to the output data
`void *` | `filter` | Pointer to the filter data
`dip_int` | `size` | Size of the input data
`dip_int` | `filterSize` | Size of the filter
`dip_int` | `origin` | Origin of the filter. Only valid in conjunction with `DIP_CNV_USE_ORIGIN`
`dipf_Convolve` | `flags` | A combination of the flags described above
`dip_Boundary` | `boundary` | One of the standard boundary conditions. See Boundary conditions

## SEE ALSO

General information about convolution

`SeparableConvolution`, `SeparableFrameWork`

DIPlib on-line documentation | Function reference | Global function index