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+.help magnify Dec98 images.imgeom
+.ih
+NAME
+magnify -- interpolate two dimensional images
+.ih
+USAGE	
+.nf
+magnify input output xmag ymag
+.fi
+.ih
+PARAMETERS
+.ls input
+List of one or two dimensional images to be magnified.  Image sections are
+allowed.  Images with an axis containing only one pixel are not magnified.
+.le
+.ls output
+List of output image names.  If the output image name is the same as the input
+image name then the magnified image replaces the input image.
+.le
+.ls xmag, ymag
+The magnification factors for the first and second image dimensions
+respectively.  The magnifications need not be integers.  Magnifications
+greater than 1 increase the size of the image while negative magnifications
+less than -1 decrease the size by the specified factor.  Magnifications
+between -1 and 1 are interpreted as reciprocal magnifications.
+.le
+.ls x1 = INDEF, x2 = INDEF
+The starting and ending coordinates in x in the input image which become
+the first and last pixel in x in the magnified image.  The values need not
+be integers.  If indefinite the values default to the first and last pixel
+in x of the input image; i.e. a value of 1 and nx.
+.le
+.ls y1 = INDEF, y2 = INDEF
+The starting and ending coordinates in y in the input image which become
+the first and last pixel in y in the magnified image.  The values need not
+be integers.  If indefinite the values default to the first and last pixel
+in y of the input image; i.e. a value of 1 and ny.
+.le
+.ls dx = INDEF, dy = INDEF
+The intervals between the output pixels in terms of the input image.
+The values need not be integers.  If these values are specified they
+override the magnification factors.
+.le
+.ls interpolant = "linear"
+The interpolant used for rebinning the image.
+The choices are the following.
+.ls nearest
+Nearest neighbor.
+.le
+.ls linear
+Bilinear interpolation in x and y.
+.le
+.ls poly3
+Third order polynomial in x and y.
+.le
+.ls poly5
+Fifth order polynomial in x and y.
+.le
+.ls spline3
+Bicubic spline.
+.le
+.ls sinc
+2D sinc interpolation. Users can specify the sinc interpolant width by
+appending a width value to the interpolant string, e.g. sinc51 specifies
+a 51 by 51 pixel wide sinc interpolant. The sinc width will be rounded up to
+the nearest odd number.  The default sinc width is 31 by 31.
+.le
+.ls lsinc
+Look-up table sinc interpolation. Users can specify the look-up table sinc
+interpolant width by appending a width value to the interpolant string, e.g.
+lsinc51 specifies a 51 by 51 pixel wide look-up table sinc interpolant. The user
+supplied sinc width will be rounded up to the nearest odd number. The default
+sinc width is 31 by 31 pixels. Users can specify the resolution of the lookup
+table sinc by appending the look-up table size in square brackets to the
+interpolant string, e.g. lsinc51[20] specifies a 20 by 20 element sinc
+look-up table interpolant with a pixel resolution of 0.05 pixels in x and y.
+The default look-up table size and resolution are 20 by 20 and 0.05 pixels
+in x and y respectively.
+.le
+.ls drizzle
+2D drizzle resampling. Users can specify the drizzle pixel fraction in x and y
+by appending a value between 0.0 and 1.0 in square brackets to the
+interpolant string, e.g. drizzle[0.5]. The default value is 1.0.
+The value 0.0 is increased internally to 0.001. Drizzle resampling
+with a pixel fraction of 1.0 in x and y is equivalent to fractional pixel
+block summing (fluxconserve = yes) or averaging (flux_conserve = no)  if
+xmag and ymag are < 1.0.
+.le
+.le
+.ls boundary = "nearest"
+Boundary extension type for references to pixels outside the bounds of the
+input image. The choices are:
+.ls nearest
+Use the value of the nearest boundary pixel.
+.le
+.ls constant
+Use a constant value.
+.le
+.ls reflect
+Generate value by reflecting about the boundary.
+.le
+.ls wrap
+Generate a value by wrapping around to the opposite side of the image.
+.le
+.le
+.ls constant = 0.
+Constant value for constant boundary extension.
+.le
+.ls fluxconserve = yes
+Preserve the total image flux.
+.le
+.ls logfile = STDOUT
+Log file for recording information about the magnification.  A null
+logfile may be used to turn off log information.
+.le
+.ih
+DESCRIPTION
+The list of input images are expanded or contracted by interpolation
+to form the output images.  The output image names are specified by the
+output list.  The number of output image names must be the
+same as the number of input images.  An output image name may be the same
+as the corresponding input image in which case the magnified image replaces
+the input image.  The input images must be one or two dimensional and each
+axis must be of at least length 2 (i.e. there have to be distinct
+endpoints between which to interpolate).
+
+The magnification factor determines the pixel step size or interval.
+Positive magnifications are related to the step size as the reciprocal;
+for example a magnification of 2.5 implies a step size of .4 and a
+magnification of .2 implies a step size of 5.  Negative magnifications
+are related to the step size as the absolute value; for example a
+magnification of -2.2 implies a step size of 2.2.  This definition
+frees the user from dealing with reciprocals and irrational numbers.
+Note that the step size may be specified directly with the parameters
+\fIdx\fR and \fIdy\fR, in which case the magnification factor is
+not required.
+
+If fluxconserve = yes, the magnification is approximately flux conserving
+in that the image values are scaled by the ratio of the output to the input
+pixel areas; i.e dx * dy.
+
+In the default case with only the magnifications specified the full
+image is expanded or contracted.  By specifying additional parameters
+the size and origin of the output image may be changed.  Only those
+parameters to be fixed need to be specified and the values of the
+remaining parameters are either determined from these values or
+default as indicated in the PARAMETERS section.
+
+The user may select the type of two dimensional interpolation and boundary
+extension to be used.  Note that the image interpolation is performed on
+the boundary extended input image.  Thus, boundary extensions which are
+discontinuous (constant and wrap) may introduce interpolation errors.
+.ih
+EXAMPLES
+1. To expand an image by a factor of 2.5:
+
+	cl> magnify imagein imageout 2.5 2.5
+
+2. To subsample the lines of an image in steps of 3.5:
+
+	cl> magnify imagein imageout dx=3.5 dy=1
+
+3. To magnify the central part of an image by 2 into a 11 by 31 image:
+
+.nf
+	cl> magnify imagein imageout 2 2 x1=25.3 x2=30.3 \
+	>>> y1=20 y2=35
+.fi
+
+4. To use a higher order interpolator with wrap around boundary extension:
+
+.nf
+	cl> magnify imagein imageout 2 2 x1=-10 y1=-10 \
+	>>> interpolation=spline3 boundary=wrap
+.fi
+
+It is important to remember that the magnification affects the pixel intervals!
+This means that the number of pixels in an expanded image is not simply
+a multiple of the original number.   The following example illustrates this
+point.  Begin with an image which is 100 by 10.  This means the
+x coordinates run between 1 and 100 and the y coordinates run between 1 and
+10 with a pixel interval of 1.
+
+Let's magnify the x axis by 0.5 and the y axis by 2.
+The output pixel intervals, in terms of the input pixel intervals,
+are then 2 and 0.5.  This means the output x pixels are at
+1, 3, 5, etc. and output y pixels are at 1, 1.5, 2, 2.5, etc., again in
+terms of the input pixel coordinates.  The last output x pixel is then
+at 99 in the input coordinates and the number of pixels is 50.  For the
+y axis the last output pixel is at 10 in the input coordinates and the
+number of pixels between 1 and 10 in intervals of 0.5 is 19!  Thus, the
+final image is 50 by 19 and not 50 by 20 which you would get if you
+multiplied the axis lengths by the magnification factors.
+
+A more complex example is given above in which x1=25.3,
+x2=30.3, y1=20, and y2=35 with magnification factors of 2.
+It is important to understand why the output image is 11 by 31 and
+what the pixel coordinates are in terms of the input pixel coordinates.
+.ih
+SEE ALSO
+imshift, blkavg, rotate, imlintran, register, geotran, geomap
+.endhelp