NAME

imshift -- shift a set of images in x and y

USAGE

imshift input output xshift yshift

PARAMETERS

input

List of images to be transformed.

output

List of output images.

xshift, yshift

Fractional pixel shift in x and y such that xout = xin + xshift and yout = yin + yshift.

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 xshift and yshift . 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.

interp_type = "linear"

The interpolant type use to computed the output shifted image. The choices are the following:

nearest

nearest neighbor.

linear

bilinear interpolation in x and y.

poly3

third order interior polynomial in x and y.

poly5

fifth order interior polynomial in x and y.

spline3

bicubic spline.

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.

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.

boundary_type = "nearest"

The choices are:

nearest

Use the value of the nearest boundary pixel.

constant

Use a constant value.

reflect

Generate value by reflecting about the boundary.

wrap

Generate a value by wrapping around to the opposite side of the image.

DESCRIPTION

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

    xout = xin + xshift
    yout = yin + yshift

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.

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

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 neighbour, bilinear, bicubic, biquintic and bicubic spline interpolants respectively (Vax 11/750 fpa).

BUGS

SEE ALSO

shiftlines, magnify, rotate, geomap, geotran, imlintran