'\" t
.ds Vv 1.2.14
.TH VistaIOZeroCrossings 3 "24 April 1993" "VistaIO Version \*(Vv"
.SH NAME
VistaIOZeroCrossings \- mark zero crossings in an image
.SH SYNOPSIS
.nf
.B "#include <vistaio.h>"
.PP
.ft B
VistaIOImage VistaIOZeroCrossings (\fIsrc\fP, \fIdest\fP, \fIband\fP)
.RS
VistaIOImage \fIsrc\fP, \fIdest\fP;
VistaIOBand \fIband\fP;
.RE
.fi
.SH ARGUMENTS
.IP \fIsrc\fP 10n
Specifies the source image in which zero crossings are to be located.
.IP \fIdest\fP
May specify a destination image to contain the results, or
.SB NULL
to indicate that a new destination image should be created.
.IP \fIband\fP
May specify a particular band of the source image to be processed,
or may be the constant \fBVistaIOAllBands\fP to indicate that all bands 
of the source image should be processed.
.SH DESCRIPTION
\fBVistaIOZeroCrossings\fP marks the zero crossings of an image. It examines
pixels of the source image, \fIsrc\fP, 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.
.PP
If the \fIdest\fP argument is
.SB NULL\c
, \fBVistaIOZeroCrossings\fP creates a destination image with the appropriate
properties. Otherwise, \fIdest\fP specifies an existing destination image to
be used.
.PP
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
\fIband\fP is \fBVistaIOAllBands\fP), or a single band (if \fIband\fP specifies
a particular band). Its pixel representation depends on that of the
source image as defined by the following table:
.PP
.TS
center ;
c c .
Source Representation	Destination Representation
_
\fBVistaIOBit\fP	\fInot supported\fP
\fBVistaIOUByte\fP	\fInot supported\fP
\fBVistaIOSByte\fP	\fBVistaIOUByte\fP
\fBVistaIOShort\fP	\fBVistaIOLong\fP
\fBVistaIOLong\fP	\fBVistaIOLong\fP
\fBVistaIOFloat\fP	\fBVistaIOFloat\fP
\fBVistaIODouble\fP	\fBVistaIODouble\fP
.TE
.SH "RETURN VALUES"
\fBVistaIOZeroCrossings\fP returns the destination image if successful and 
.SB NULL
otherwise.
.SH "SEE ALSO"
.na
.nh
.BR VistaIOCanny (3),
.BR VistaIOLinkImage (3),
.BR VistaIOImage (3),

.hy
.ad
.SH NOTES
\fBVistaIOZeroCrossings\fP labels the destination image as a gradient image by
giving it the attributes \fBncomponents:\ 1\fP and 
\fBcomponent_interp: gradient\fP.
.SH DIAGNOSTICS
.IP "``Band \fIband\fP referenced in image of \fInbands\fP band(s).''"
The \fIband\fP argument is invalid given the number of bands in \fIsrc\fP.
.IP "``Source image has unsigned pixels.''"
How can an image of unsigned pixels have zero crossings? Such source images
are not supported.
.IP "``Destination image has \fIdest_nbands\fP bands; \fIsrc_nbands\fP expected.''"
A destination image was specified but it has the wrong number of bands.
If \fIband\fP is \fBVistaIOAllBands\fP, the destination image must have the same
number of bands as the source image. Otherwise, it must have a single
band.
.IP "``Destination image has \fIdest_prop\fP \fIproperty\fP; \fIsrc_prop\fP expected.''"
\fIProperty\fP 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.
.SH AUTHORS
.na
.nh
David\ Lowe\ <lowe@cs.ubc.ca>,\ Art\ Pope\ <pope@cs.ubc.ca>

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