SKYPROCESS

Purpose :

Statistical analysis and smoothing of the cell pixel distributiton find the sky background level across the plate, and construct a properly sampled "snapshot" image of the entire plate.

Procedure :

The Sky Sigma is computed by taking the mode of the distribution of the individual cell rms values. The "Snapshot" is created by taking the sigma clipped mean value for each of the cells and saving this as an image (SNP file). The computation of the SKY image is performed by taking the median values of each cell and then running a sequence of median filters at different scales (8,4,2,1 cells) to smooth out the image over these scales. The mean and rms of this smoothed image is then computed. Although this smoothed image is the computed sky background, in an attempt to avoid processing the "Bad" edges of the plate and the label and sensitometer areas the edges of the sky image are examined for areas which the data is more than 5 sigma away from the mean sky are set negative. This is a flag for the Object Detection program to avoid processing.

User Restriction :

Set default to the directory containing the data before running the task. This is necessary to workaround a bugs that will be fixed in the future.

Calling Sequence :

SKYPROCESS SIMfile
[/XPOS=x] Starting corner to analyse (no longer supported) {default 1}
[/YPOS=y] Starting corner to analyse (no longer supported) {default 1}
[/XSIZE=nx] Size of area to analyse (no longer supported) {default 720}
[/YSIZE=ny] Size of area to analyse (no longer supported) {default 720}
[/K_VALUE=k] k sigma clipping value {def=2.5}
useful range min=0.5 max=infinity
(-) values allowed -x.y gives +x*sigma -y*sigma
[/TOLERANCE=t] convergence tolerance for clipping {def=25}
useful range: min=1 max=32767
[/MAX_ITER=i] max.iterations of clipping {def=10}
useful range: min=1 max=10000
[/[no]SMOOTH=(p,q,r,...] Apply repeated median filters on specified scales {def=(8,4,2,1)}
you can specify up to 8 integers for smoothing
each must be in the range min=1 max=image dim(sky pixels) / 2
[/[no]MASK] Apply edge mask {def}
[/MASK_ENLARGE=] Enlarge mask by imagesize/mask_enlarge {def=34}
# of pixels to enlarge mask = dim image in sky pixels / mask_enlarge
useful range: min=2 max=x or y dimension of image in sky pixels
[/MASKDIR="String"] mask file directory location
[/COMMENT="String"] Comment for DID file
[/[no]ANNOTATE] Write results {def}
[/NEW] Write new DID file
[/DEBUG]

Availability :

History/Author :

Original Implementation - Brian McLean
Brian McLean ---- mclean@stsci.edu