IRAF help page for package images, program lineclean

• input
• output
• sample = *
• naverage = 1
• function = spline3
• legendre
• chebyshev
• spline1
• spline3
• order = 1
• low_reject = 2.5, high_reject = 2.5
• niterate = 1
• grow = 1.
• graphics = stdgraph
• cursor = stdgcur

lineclean input output

PARAMETERS

input

output

sample = *

naverage = 1

function = spline3

chebyshev

spline1

spline3

order = 1

low_reject = 2.5, high_reject = 2.5

niterate = 1

grow = 1.

graphics = stdgraph

cursor = stdgcur

A one dimensional function is fit to each line of the input images. The function may be a legendre polynomial, chebyshev polynomial, linear spline, or cubic spline of a given order or number of spline pieces. If low_reject and/or high_reject are greater than zero the sigma of the residuals between the fitted points and the fitted function is computed and those points whose residuals are less than -low_reject * sigma and greater than high_reject * sigma are excluded from the fit. Points within a distance of grow pixels of a rejected pixel are also excluded from the fit. The function is then refit without the rejected points. This rejection procedure may be iterated a number of times given by the parameter niterate. Finally, the rejected points in the input image are replaced by the fitted values to create the output image lines.

The output image may exist in which case a section in the input image is applied to the output image. Thus, a section on the input image causes only that part of the output image to be cleaned. If the output image does not exist it is first created by making a copy of the full (without a section) input image.

The points fit are determined by selecting a sample of columns specified by the parameter sample and taking either the average or median of the number of points specified by the parameter naverage. The type of averaging is selected by the sign of the parameter and the number of points is selected by the absolute value of the parameter. The sample points are specified relative to any image section.

The fitting parameters (sample, naverage, function, order, low_reject, high_reject, niterate, grow) may be adjusted interactively if the parameter interactive is yes. Lines from the image are selected to be fit with the icfit package. For images of greater than two dimensions sets of numbers giving the 2nd, 3rd, etc. coordinates are entered. The image lines are specified relative to any image section. When an end-of-file or no line is given then the last selected fitting parameters are used on each line of the image. This step is repeated for each image in the input list. The interactive options are described in the help information icfit.