CDIST-S-distortion correction using SDIST results

Description:

Applies the distortion correction determined by SDIST to an image.

Parameters:

IMAGE

The name of the S-distorted image that is to be corrected.

YSTART

If the image contains, for example, a single spectrum in the center and a lot of unused background at the edges, it can save processing time if only a part of the Y-range of the data is corrected. YSTART is the first Y value in the range corrected by CDIST.

YEND

Specifies the last Y value in the range corrected by CDIST.

OUTPUT

Specifies the name of the resulting, corrected, image. If OUTPUT is different to IMAGE, a new image will be created. If it is the same, the correction will be performed in situ.

MAXDEGY

If a number of spectra have been used to determine the image distortion, CDIST interpolates between their fitted positions by fitting a low order polynomial to them. MAXDEGY specifies the order of this polynomial.

ROTATE

The processing performed by CDIST normally involves accessing the image in a way that causes excessive paging on the VAX. This paging may be considerably reduced by rotating the image (in a relatively efficient way) before and after the correction. Of course, this introduces the overhead of the two rotations. Generally, large images should be rotated, small images should not. The results should be identical in both cases.

Source comments:

 C D I S T

 Performs an S-distortion correction for an image, using the
 distortion analysis provided by SDIST.  If the SDIST analysis
 was for a single spectrum, the the correction is '1-dimensional'
 in that it consists simply of applying a shift in Y to the
 data for each column of the image.  The shift is determined
 separately for each column from the polynomial fitted by SDIST.
 If the SDIST analysis was for more than one spectrum, the
 correction is what might be termed '1.5-dimensional' - the
 data is only redistributed within columns, but the amount of
 shift varies along each column in a manner determined by fitting
 a low order polynomial to the results of evaluating the polynomials
 that SDIST fitted to each spectrum.  The 1.5D algorithm actually
 reduces to the 1-D case when there is only one spectrum, but it
 simplifies things to think of them as distinct cases.

 Command parameters -

 IMAGE    (Character) The name of the image to be corrected.

 YSTART   (Numeric) The first Y value to be used.

 YEND     (Numeric) The last Y value to be used.  Using YSTART
          and YEND to limit the range of data corrected will
          speed up the operation.

 OUTPUT   (Character) The name of the resulting image.  This
          can be the same as IMAGE, in which case the correction
          will be performed in situ.

 MAXDEGY  (Numeric) The maximum degree polynomial to fit to the
          spectral positions in the case where there is more
          than one spectrum covered by the SDIST analysis.

 Command keywords -

 ROTATE   If set, the image to be corrected will be rotated
          prior to the application of the correction.  This
          minimises the number of page faults during the correction,
          but at the expense of the overheads of the rotation itself.

 User variables - None

 Input files -

 SDIST.DAT contains the results of the fit(s), as written by
           SDIST, in a format treated as follows -

           3 header lines, all beginning with '*'
           One line giving the number of spectra traced, in the
           format 20X,I5.
           Then, for each spectrum traced, one record giving
           the spectrum number, and the leftmost and rightmost
           pixels covered by the trace, in format
           11X,I5,17X,I5,4X,I5, then 1 record giving the average
           Y value in the spectrum, in format 16X,F13.7,
           which is followed by 3 records giving the 11
           polynomial coefficients for the fit, in 3D23.16.
           Coefficients are given constant first, with any unused
           coefficients set to zero.

                                          KS / CIT 6th Feb 1984