VIG-Corrects a 2D array for vignetting

Description:

This routine accepts a sky or flat field IMAGE obtained at the same filter for imaging , or at the same grating angle as a series of spectra which need to be corrected for vignetting in 2D. Two orthogonal one dimensional cuts through the 2D IMAGE are formed and fitted with Chebyshev polynomials to form flattening functions on the respective axes. The correction applied to the data is formed from the product of the terms of each of these two series. Because the correction IMAGES may include unwanted signals, such as sky lines the users can specify regions of the data which may be excluded from the fits. In practice rather actaully restructure the template cuts formed in the two directions,by deleteing these data this is achieved by ascribing them a very low weight in the fitting process. At the current time it has been found that a wright of 1E-6 is an effective way of elimanting such points.

Parameters:

IMAGE

IMAGE = FILE (Read) Name of image for input

OLD

OLD = LOGICAL (Read) old coefficients are to be used for correction

OUTPUT

OUTPUT = FILE (Write) OUTput Name of output file OUTPUT is the name of the resulting image. If OUTPUT is the same as INPUT the data in the input file will be modified in situ.Otherwise a new file will be created.

YSTART

YSTART = INTEGER (Read) start value to extract in channel direction The data between the limits ystart and yend is extracted and the resultant spectrum is used to find the vignetting in the channel direction.

YEND

YEND = INTEGER (Read) end value to extract in channel direction The data between the limits ystart and yend is extracted and the resultant spectrum is used to find the vignetting in the channel direction.

XSTART

XSTART = INTEGER (Read) start value to extract in x-sect direction The data between the limits xstart and xend is extracted and the resultant spectrum is used to find the vignetting in the cross-section direction.

XEND

XEND = INTEGER (Read) end value to extract in x-sect direction The data between the limits xstart and xend is extracted and the resultant spectrum is used to find the vignetting in the cross-section direction.

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