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CONVOLUTION(3)                                                  CONVOLUTION(3)




NAME

       im_conv,  im_convf,  im_convsep,  im_convsepf,  im_convsub, im_shrink -
       convolves an image with a generalised mask


SYNOPSIS

       #include <vips/vips.h>

       int im_conv(in, out, mask)
       IMAGE *in, *out;
       INTMASK *mask;

       int im_convf(in, out, mask)
       IMAGE *in, *out;
       DOUBLEMASK *mask;

       int im_convsep(in, out, mask)
       IMAGE *in, *out;
       INTMASK *mask;

       int im_convsepf(in, out, mask)
       IMAGE *in, *out;
       DOUBLEMASK *mask;

       int im_convsub(in, out, mask, xskip, yskip)
       IMAGE *in, *out;
       INTMASK *mask;
       int xskip, yskip;

       int im_shrink(in, out, xfactor, yfactor)
       IMAGE *in, *out;
       double xfactor, yfactor;



DESCRIPTION

       These functions convolve the image pointed by the image  descriptor  in
       with  the file pointed by mask and puts the result in the image pointed
       by out.  The mask structures INTMASK and DOUBLEMASK are returned by the
       function  im_read_imask(3)  or im_read_dmask(3), for integer and double
       masks respectively.

       Input should be non-complex.  The size and type of the output image are
       the  same as the size of the input.  To output a larger type (for exam-
       ple, to output an int image from convolution of a byte image,  avoiding
       clipping),  cast  the  input image up with one of the im_clip2*() func-
       tions.

       If the sizes of the mask are xm and ym and the sizes of the  image  are
       xs and ys, then there is a black border at the output image as follows:

       The top ym/2 lines black, bottom ys-ym/2-ym lines black;  each  of  the
       remaining  lines  has  the  initial  xm/2 pels blank, and the final xs-
       xm/2-xm pels (division over 2 is integer division).

       The output at each point is divided by scale and  then  the  offset  is
       added.  Both offset and scale are held in mask.

       im_conv()  and  im_convsep()  have  'raw' versions which do not add the
       black border: instead the output image is smaller than the input.

       im_conv() and im_conv_raw() convolve any  non-complex  input  image  to
       make  an  output image of the same type. Rounding is appropriate to the
       image type.

       im_convf() convolves to float (double if the  input  is  double).   The
       function expects a double mask.

       im_convsep() and im_convsep_raw() carry out convolution using an 1xN or
       Nx1 separable mask.

       The function scales the output result by dividing it with  scale*scale.
       The  scale  factor  should  therefore  be  the sqrt of the scale of the
       square NxN mask.

       Rounding is appropriate to the image type.  It works on any non-complex
       image,  and  writes  the  output  in the same format as the input.  The
       function expects integer mask.

       im_convsepf() convolves to float (double if the input is double).   The
       function expects a double mask.

       im_convsub()  convolves  the  byte  image  pointed by in and writes the
       result as a byte output.  Using this function the input image  is  sub-
       sampled  on  both directions by an integer factor of xskip horizontally
       and an integer factor of yskip vertically.  During the covolution, val-
       ues  are  rounded  before  division.   Both input and output are bytes.
       Output is clipped between 0 and 255.  The function expects  an  integer
       mask.

       im_shrink() shrink the input image file by xfactor along the horizontal
       and yfactor along the vertical direction.  The function doesnot perform
       subpixel  interpolation  and  therefore the resultant image can present
       aliasing especially for small x and y factors. Any size image, any non-
       complex type, any number of bands.


RETURN VALUE

       The function returns 0 on success and -1 on error.


SEE ALSO

       im_read_imask(3), im_compass(3), im_fastcor(3).



                                  2 May 1991                    CONVOLUTION(3)

im_conv_raw 7.14.5 - Generated Sat Sep 6 09:02:56 CDT 2008
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