NAME

       VistaIOZeroCrossings - mark zero crossings in an image

SYNOPSIS

       #include <vistaio.h>

       VistaIOImage VistaIOZeroCrossings (src, dest, band)
              VistaIOImage src, dest;
              VistaIOBand band;

ARGUMENTS

       src       Specifies the source image in which zero crossings are to be located.

       dest      May  specify  a  destination  image  to  contain  the  results,  or NULL to indicate that a new
                 destination image should be created.

       band      May specify a particular band of the source image to be  processed,  or  may  be  the  constant
                 VistaIOAllBands to indicate that all bands of the source image should be processed.

DESCRIPTION

       VistaIOZeroCrossings  marks  the zero crossings of an image. It examines pixels of the source image, src,
       and sets destination pixels according to whether they correspond to  zero  crossings.  If  a  destination
       pixel  does  not  lie on a zero crossing, it is set to zero. If it does, it is set to the gradient of the
       zero crossing. The gradient is simply computed as the magnitude of the difference between pixels on  each
       side of the zero crossing.

       If  the  dest  argument  is  NULL,  VistaIOZeroCrossings creates a destination image with the appropriate
       properties. Otherwise, dest specifies an existing destination image to be used.

       The destination image is smaller than the source image by one row and one column. It has either the  same
       number  of  bands as the source image (if band is VistaIOAllBands), or a single band (if band specifies a
       particular band). Its pixel representation depends on  that  of  the  source  image  as  defined  by  the
       following table:

                                  Source Representation   Destination Representation
                                  ───────────────────────────────────────────────────
                                       VistaIOBit               not supported
                                      VistaIOUByte              not supported
                                      VistaIOSByte               VistaIOUByte
                                      VistaIOShort               VistaIOLong
                                       VistaIOLong               VistaIOLong
                                      VistaIOFloat               VistaIOFloat
                                      VistaIODouble             VistaIODouble

RETURN VALUES

       VistaIOZeroCrossings returns the destination image if successful and NULL otherwise.

SEE ALSO

       VistaIOCanny(3), VistaIOLinkImage(3), VistaIOImage(3),

NOTES

       VistaIOZeroCrossings labels the destination image as a gradient image by giving it the attributes ncompo‐
       nents: 1 and component_interp: gradient.

DIAGNOSTICS

       ``Band band referenced in image of nbands band(s).''
              The band argument is invalid given the number of bands in src.

       ``Source image has unsigned pixels.''
              How can an image of unsigned pixels have zero crossings? Such source images are not supported.

       ``Destination image has dest_nbands bands; src_nbands expected.''
              A  destination  image  was specified but it has the wrong number of bands.  If band is VistaIOAll‐
              Bands, the destination image must have the same number of bands as the source image. Otherwise, it
              must have a single band.

       ``Destination image has dest_prop property; src_prop expected.''
              Property is one of ``pixels'', ``rows'', or ``columns''.  A destination image was specified but it
              does not have the same pixel representation, number of rows, and number of columns as  the  source
              image.

AUTHORS

       David Lowe <lowe@cs.ubc.ca>, Art Pope <pope@cs.ubc.ca>

       Adaption to vistaio: Gert Wollny <gw.fossdev@gmail.com>

VistaIO Version 1.2.14                            24 April 1993                          VistaIOZeroCrossings(3)