shift -- Shift an image by a specified number of pixels.
shift input output shift
This routine shifts the contents of either a 1- or 2-dimensional image by a specified integral number of pixels. The amount of shift can be specified as either "center" or "decenter", in which case the shift will be calculated as it would in other tasks in the fourier package. After shifting the image, this task will update the value of the CRPIX1 keyword (and CRPIX2 for a 2- dimensional image.
- input = "" [file name template]
- Names of the image(s) to be shifted.
The convention for real and imaginary parts used elsewhere in the fourier package is ignored for this task. The file name passed to this parameter should be the full file name---no "r" or "i" will be appended. The name must therefore be given twice if both real and imaginary parts are to be shifted, or a wildcard character (such as "*") must be used.
- output = "" [file name template]
- File names for the shifted output images.
If output is null, then input files will be modified in-place. If any value is passed to output, then output must be passed the same number of values as were passed to input. If the same name is given for an input file and its corresponding output file, then that file will be modified in-place.
- shift = "center" [string]
- Amount of shift, in pixels.
The amount of shift may be given as a number, or it may be either "center" or "decenter". (Only the first letter "c" or "d" is significant).
A shift of +5 means that the value at pixel 1 will be moved to pixel 6. If shift=center, then shift is calculated as (npix/2), where npix is the number of pixels in the image (with fractions truncated). If shift=decenter, then shift will correspond to a value of (-npix/2)--this will have a different effect from shift=center when npix is an odd number.
If numbers are passed to shift when working with 2- dimensional images, then two numbers---separated by whitespace---must be passed; a single value will not be used for both images as is would the "decenter" or "center" options. If "center" and "decenter" options are desired, then they can be abbreviated, for example, shift=center,center can be abbreviated shift=center. The same shift parameter will be applied to all files, but this can result in different shift VALUES. If shift=center or shift=decenter, the amount of shift will depend on the size of the file.
- (verbose = yes) [boolean]
- Display the names of files as they are processed?
1. The 2-dimensional real and imaginary parts (hd446r and hd446i) are to be centered in the second axis, but not in the first. The following will center them in the second axis without changing the first; they are modified in-place:
fo> shift "hd446r,hd446i" "" "0 center"
Type "help fourier opt=sys" for a higher-level description of the fourier package.