profoundChisel: Noise Chisel Esque Sky

In ProFound: Photometry Tools

Description

This is an implementation of a Noise Chisel like approach method of identifying sky pixels. It is conceptually similar on some regards, but does not attempt to produce the same solutions (i.e. it is more like "inspired by").

Usage

profoundChisel(image = NULL, sky = NULL, skythresh = 0.005, blurcut = 0.01,
objthresh = 1 - skythresh, sigma = 2, iterchisel = 5, itersky = 5,
objbias = 0.5, box = 100, skyconv = 0.01)

Arguments

image	Numeric matrix; required, the image we want to analyse. Note, image NAs are treated as masked pixels.
sky	User provided estimate of the absolute sky level. Can be a scalar or a matrix matching the dimensions of image (allows values to vary per pixel). This will be subtracted off the image internally, so only provide this if the sky does need to be subtracted!
skythresh	Numeric scalar; the quantile level to use to identify sink pixels for the sky (so should be between 0 and 1).
blurcut	Numeric scalar; PDF level to cut the blurring kernel at when dilating. Lower values mean larger dilations.
objthresh	Numeric scalar; the quantile level to use to identify source pixels for real objects (so should be between 0 and 1).
sigma	Numeric scalar; standard deviation of the blur used. This should be well matched to the PSF of the image in most cases.
iterchisel	Integer scalar; how many iterations of the inner chisel routine to run for.
itersky	Integer scalar; how many iterations of the outer sky estimation routine to run for.
objbias	Numeric scalar; how much to bias the dilations towards assuming pixels belong to objects (larger values mean more object pixels will in general be created).
box	Integer scalar; the dimensions of the box car filter to estimate the sky with.
skyconv	Numeric scalar; when <= skyconv fraction of pixels change sky/object designation, the solution is considered converged and itersky iterations stop.

Details

This is an implementation of a Noise Chisel like approach method of identifying sky pixels. It is conceptually similar on some regards, but does not attempt to produce the same solutions (i.e. it is more like "inspired by").

Value

A list with two parts:

objects	Logical matrix; the object map matched pixel by pixel to image. 1 means there is an object at this pixel, 0 means it is a sky pixel. Can be used as a mask in various other functions that require objects to be masked out.
sky	The estimated sky level of the image.

Author(s)

Aaron Robotham

References

Akhlaghi et al, 2015, ApJSS, 220, 1

See Also

profoundMakeSkyGrid

Examples

image=readFITS(system.file("extdata", 'VIKING/mystery_VIKING_Z.fits',
package="ProFound"))$imDat
magimage(profoundChisel(image)$objects)

ProFound documentation built on Jan. 8, 2021, 5:37 p.m.