.help imshift Dec98 images.imgeom
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NAME
imshift -- shift a set of images in x and y
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USAGE
imshift input output xshift yshift
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PARAMETERS
.ls input
List of images to be transformed.
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.ls output
List of output images.
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.ls xshift, yshift
Fractional pixel shift in x and y such that xout = xin + xshift and
yout = yin + yshift.
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.ls shifts_file = ""
The name of the text file containing the shifts for each input image. If no
file name is supplied each input image is shifted by \fIxshift\fR and
\fIyshift\fR. Shifts are listed in the text file, 1 set of shifts per image,
with the x and y shift in columns 1 and 2 respectively. The number of
shifts in the file must equal the number of input images.
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.ls interp_type = "linear"
The interpolant type use to computed the output shifted image.
The choices are the following:
.ls nearest
nearest neighbor.
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.ls linear
bilinear interpolation in x and y.
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.ls poly3
third order interior polynomial in x and y.
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.ls poly5
fifth order interior polynomial in x and y.
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.ls spline3
bicubic spline.
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.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 input by the
user will be rounded up to the nearest odd number. The default sinc width
is 31 by 31.
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.ls drizzle
2D drizzle resampling. Users can specify the drizzle pixel fractions in x and y
by appending values 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 to 0.001. Drizzle resampling with a pixel fraction
of 1.0 in x and y is identical to bilinear interpolation.
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.le
.ls boundary_type = "nearest"
The choices are:
.ls nearest
Use the value of the nearest boundary pixel.
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.ls constant
Use a constant value.
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.ls reflect
Generate value by reflecting about the boundary.
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.ls wrap
Generate a value by wrapping around to the opposite side of the image.
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.le
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DESCRIPTION

IMSHIFT will shift an image in x and y such that:

.nf
    xout = xin + xshift
    yout = yin + yshift

.fi

The output image gray levels are determined by interpolating in the input
image at the positions of the shifted output pixels.
IMSHIFT uses the routines in the 2-D interpolator package.

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EXAMPLES

1. Shift an image by (+3.2, -4.5) using a biquintic interior polynomial
   interpolant and boundary extension.

   cl> imshift vys70 vys70shift 3.2 -4.5 inter=poly5 bound=neare

2. Shift an image by (-6., 1.2) using bilinear interpolation and
   boundary extension.

   cl> imshift ugc1040 ugc1040shift -6.0 1.2 bound=neare

3. Shift a set of images using shifts listed in the textfile "shifts".

   cl> page shifts

       3.5  4.86
       -2.  8.9
       10.1 7.8

   cl> imshift im1,im2,im3 im1.s,im2.s,im3.s shifts_file=shifts

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TIMINGS
The time required to shift a 512 by 512 real image by fractional pixel
amounts in x and y is approximately 10, 20, 70, 120, and 120 cpu seconds for the
nearest neighbor, bilinear, bicubic, biquintic and bicubic spline
interpolants respectively (Vax 11/750 fpa).

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BUGS
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SEE ALSO
shiftlines, magnify, rotate, geomap, geotran, imlintran
.endhelp