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+.help extras Sep95 noao.twodspec.apextract
+.ih
+NAME
+extras -- Information about the extra bands in 3D output
+.ih
+DESCRIPTION
+When one dimensional spectra are extracted by the tasks in the
+\fBapextract\fR package the user may specify that additional
+extra associated information be extracted at the same time.  This
+information is produced when the \fIextras\fR parameter is "yes".
+
+The associated information is recorded as additional "bands" (the IRAF term
+for the third dimension of a three dimensional image) of the output
+extracted spectral image.  Extracted spectra are currently stored as IRAF
+images with dispersion information given in the image header.  The
+image axes for such images are:
+
+.nf
+    1 (columns) - dispersion axis
+    2 (lines)   - spectrum axis (each line is a separate spectrum)
+    3 (bands)   - extras axis (each band is associated data)
+.fi
+
+The lengths of the second and third axes, that is the number of
+lines and bands, may be one or more.  If there is only one band
+the image will be two dimensional and if there is only one line
+and one band the image will be one dimensional.  Note that the
+\fIformat\fR parameter controls whether multiple apertures are
+written to separate images or to a single image.  Thus, if
+the format is "onedspec" this means that the second dimension
+will always be of length one and, if the \fIextras\fR parameter
+is no, the output images will be one dimensional.
+
+The associated data in the image bands depends on which extraction
+options are performed.  The various types of data are:
+
+.nf
+    The primary spectrum flux values.
+    Simple aperture sum if variance weighting or cleaning was done.
+    Background spectrum if background subtraction was done.
+    Sigma spectrum if variance weighting or cleaning was done.
+.fi
+
+The primary spectrum is always the first band and will be the cleaned
+and/or variance weighted and/or background subtracted spectrum.  The
+simple aperture sum spectrum allows comparing against the results of the
+variance weighting or pixel rejection options.  When background
+subtraction is performed the subtracted background is recorded in
+one of the bands.  When variance weighting or pixel rejection is
+performed the software generates an estimate of the uncertainty
+in the extracted flux as a sigma.
+
+The identity of the various bands is given by the image header
+keywords BANDIDn (where n is the band number).  This also serves
+to document which extraction options were used.
+
+For more information get help under the topic "apextract.package".
+.ih
+SEE ALSO
+apextract.package
+.endhelp