Name

lccdproc -- Process LRIS images

Usage

ccdproc images

Parameters

images: List of input CCD images to process. The list may include processed images and calibration images.
ccdtype = "": CCD image type to select from the input image list. If no type is given then all input images will be selected. The recognized types are described in ccdtypes.
max_cache = 0: Maximum image caching memory (in Mbytes). If there is sufficient memory the calibration images, such as zero level, dark count, and flat fields, will be cached in memory when processing many input images. This reduces the disk I/O and makes the task run a little faster. If the value is zero image caching is not used.
noproc = no: List processing steps only?

Processing Switches

fixpix = yes: Fix bad CCD lines and columns by linear interpolation from neighboring lines and columns? If yes then a bad pixel mask, image, or file must be specified.
overscan = yes: Apply overscan or prescan bias correction? If yes then the overscan image section will be determined from the keywords in the image header.
trim = yes: Trim the image of the overscan region and bad edge lines and columns? If yes then the data section will be determined from the keywords in the image header.
zerocor = yes: Apply zero level correction? If yes a zero level image must be specified.
darkcor = yes: Apply dark count correction? If yes a dark count image must be specified.
flatcor = yes: Apply flat field correction? If yes flat field images must be specified.
illumcor = no: Apply illumination correction? If yes illumination images must be specified.
fringecor = no: Apply fringe correction? If yes fringe images must be specified.
readcor = no: Convert zero level images to readout correction images? If yes then zero level images are averaged across the readout axis to form one dimensional zero level readout correction images.
scancor = no: Convert zero level, dark count and flat field images to scan mode flat field images? If yes then the form of scan mode correction is specified by the parameter scantype.

Processing Parameters

readaxis = "line"

Read out axis specified as "line" or "column".

fixfile

Bad pixel mask, image, or file. If "image" is specified then the name is specified in the image header or instrument translation file. If "BPM" is specified then the standard BPM image header keyword defines a bad pixel mask. A bad pixel mask is a compact format (".pl" extension) with zero values indicating good pixels and non-zero values indicating bad pixels. A bad pixel image is a regular image in which zero values are good pixels and non-zero values are bad pixels. A bad pixel file specifies bad pixels or rectangular bad pixel regions as described later. The direction of interpolation is determined by the mask value with a value of two interpolating across columns, a value of three interpolating across lines, and any other non-zero value interpolating along the narrowest dimension.

zero = ""

Zero level calibration image. The zero level image may be one or two dimensional. The CCD image type and subset are not checked for these images and they take precedence over any zero level calibration images given in the input list.

dark = ""

Dark count calibration image. The CCD image type and subset are not checked for these images and they take precedence over any dark count calibration images given in the input list.

flat = ""

Flat field calibration images. The flat field images may be one or two dimensional. The CCD image type is not checked for these images and they take precedence over any flat field calibration images given in the input list. The flat field image with the same subset as the input image being processed is selected.

illum = ""

Illumination correction images. The CCD image type is not checked for these images and they take precedence over any illumination correction images given in the input list. The illumination image with the same subset as the input image being processed is selected.

fringe = ""

Fringe correction images. The CCD image type is not checked for these images and they take precedence over any fringe correction images given in the input list. The fringe image with the same subset as the input image being processed is selected.

minreplace = 1.

When processing flat fields, pixel values below this value (after all other processing such as overscan, zero, and dark corrections) are replaced by this value. This allows flat fields processed by ccdproc to be certain to avoid divide by zero problems when applied to object images.

scantype = "shortscan"

Type of scan format used in creating the CCD images. The modes are:

"shortscan": The CCD is scanned over a number of lines and then read out as a regular two dimensional image. In this mode unscanned zero level, dark count and flat fields are numerically scanned to form scanned flat fields comparable to the observations.
"longscan": In this mode the CCD is clocked and read out continuously to form a long strip. Flat fields are averaged across the readout axis to form a one dimensional flat field readout correction image. This assumes that all recorded image lines are clocked over the entire active area of the CCD.

nscan

Number of object scan readout lines used in short scan mode. This parameter is used when the scan type is "shortscan" and the number of scan lines cannot be determined from the object image header (using the keyword nscanrows or it's translation).

Overscan Fitting Parameters

There are two types of overscan (or prescan) determinations. One determines a independent overscan value for each line and is only available for a readaxis of 1. The other averages the overscan along the readout direction to make an overscan vector, fits a smoothing function to the vector, and then evaluate and then evaluates the smooth function at each readout line or column. The line-by-line determination only uses the function parameter and the smoothing determinations uses all the following parameters.

interactive = no

Fit the overscan vector interactively? If yes and the overscan function type is one of the icfit types then the average overscan vector is fit interactively using the icfit package. If no then the fitting parameters given below are used.

function = "legendre"

Line-by-line determination of the overscan is specified by:

average - the average of the biassec columns at each line
median - the median of the biassec columns at each line
minmax - the average at each line with the min and max excluded

The smoothed overscan vector may be fit by one of the functions:

legendre - legendre polynomial
chebyshev - chebyshev polynomial
spline1 - linear spline
spline3 - cubic spline

order = 1

Number of polynomial terms or spline pieces in the overscan fit.

sample = "*"

Sample points to use in the overscan fit. The string "*" specifies all points otherwise an icfit range string is used.

naverage = 1

Number of points to average or median to form fitting points. Positive numbers specify averages and negative numbers specify medians.

niterate = 1

Number of rejection interations to remove deviant points from the overscan fit. If 0 then no points are rejected.

low_reject = 3., high_reject = 3.

Low and high sigma rejection factors for rejecting deviant points from the overscan fit.

grow = 0.

One dimensional growing radius for rejection of neighbors to deviant points.

Detector Parameters

rdnoise: CCD readout noise in electrons per pixel. If specified, the value is written to the image header as the keyword rdnoise.
gain: CCD inverse gain in electrons per ADU. If specified, the value is stored in the image header as the keyword gain.

Description

lccdproc is a version of the customary noao.imred.ccdred.ccdproc task specifically modified for use with LRIS. The only substantive changes are as follows:

Overscan subtraction is performed by invoking the lrisbias task which reduces properly data taken in both single- or dual-amp mode.
The overscan region(s) and trim data section are determined automatically from keywords present in the image header.
The readout noise and gain, if specified, are stored in the image header for future reference.

After removing the overscan and trimming the image with lrisbias, this task invokes the ccdproc task to complete the data reduction.

Author

Gregory D. Wirth, W. M. Keck Observatory

Revisions

lccdproc v0.0 1999-Feb-24: Original release.