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 ncomponents: 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
              VistaIOAllBands,  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>