NAME

lineclean -- replace deviant pixels in image lines

USAGE

lineclean input output

PARAMETERS

input

Input images to be cleaned.

output

Output cleaned images. The number of output images must be the same as the number of input images.

sample = "*"

Columns to be used in fitting the cleaning function.

naverage = 1

Number of sample points to combined to create a fitting point. A positive value specifies an average and a negative value specifies a median.

function = spline3

Cleaning function to be fit to the image lines. The functions are:

legendre

Legendre polynomial of the specified order.

chebyshev

Chebyshev polynomial of the specified order.

spline1

Linear spline of the specified number of pieces.

spline3

Cubic spline of the specified number of pieces.

order = 1

The order of the polynomials or the number of spline pieces.

low_reject = 2.5, high_reject = 2.5

Rejection limits below and above the fit in units of the residual sigma.

niterate = 1

Number of rejection iterations.

grow = 1.

When a pixel is rejected, pixels within this distance of the rejected pixel are also rejected.

graphics = "stdgraph"

Graphics output device for interactive graphics.

cursor = "stdgcur"

Graphics cursor input.

DESCRIPTION

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 .

EXAMPLES

1. To clean pixels deviating by more than 2.5 sigma:

cl> lineclean image cleanimage

If the interactive flag is set then a prompt for an image line is printed:

image: Fit line = 100

For a one or two dimensional image the line number is entered (1 for a one dimensional image). For a three dimensional image two numbers are entered. For example:

image: Fit line = 10 2

for line 10 of the second image plane.

The selected line is graphed and the interactive options for setting and fitting the line are used. Data points marked with diamonds indicate points to be replaced by the fitted value. Exiting with q or return prompts for another line. When the fitting parameters are suitably set then respond with end-of-file or return to fit all the lines of the image and create the output image.

SEE ALSO

fit1d, xtools.icfit, imsurfit