ProFound: Photometry Tools

profoundSkyScan

R Documentation

Remove Sensor 1/f Noise

Description

Removes classic row and column noise artefacts that are common the CCDs and CMOS due to 1/f read noise and other electronic effects.

Usage

profoundSkyScan(image, mask = NULL, clip = c(0,1), scan_block = dim(image),
  sky_quan = 0.4, scan_direction = 'xy', good_frac = 0, keep_trend = TRUE,
  trend_block = 21)

Arguments

`image`	Numeric matrix; required, the image we want to analyse. Note, image NAs are treated as masked pixels.
`mask`	Boolean matrix; optional, object mask where 1 is object and 0 is sky. If provided, this matrix must be the same dimensions as image.
`clip`	Numeric scalar; the quantile clip level to apply to the internal scan blocks to remove bright real sources. The default does nothing, and is probably only appropriate when keep_trend = TRUE.
`scan_block`	Integer vector; the scan blocks to use for x/rows (x direction) and y/columns (y direction). Generally larger means less aggressive feature removal. These must be integer divisors of dim(numeric).
`sky_quan`	Numeric scalar; the quantile level to analyse to remove 1/f features. Lower is generally better, but too low is bad because you can hit negative pixel artefacts too.
`scan_direction`	Character scalar; how to scan image. Either x then y (default), y the x, just x or just y.
`good_frac`	Integer scalar; the fraction of real values pixels that must be available on a scan block for the value to be trusted (at the extreme this would be not compute the median of a single value).
`keep_trend`	Logical; should large scale trends (correlations between neighbouring scan blocks) be preserved? Usually the answer to this will be TRUE, to not self subtract e.g. large galaxies from themselves. If in a very empty field with not "real" large scale trends then a better answer might be FALSE.
`trend_block`	Integer scalar; the size of the running median to use to detect and recover large scalre trends when keep_trend = TRUE.

Details

If scan_direction = 'xy' the code first scans blocks of the image in rows of x of size scan_block[1]. It clips out masked pixels, pixels below clip[1], and pixels above the quantile cut implied by clip[2]. It then detects the quantile defined by sky_quan, and the median of all blocks analysed is removed before the row wise 1/f map is reconstructed (i.e. the sky pedestal will remain intact, and only variations around this are removed).

The code next does a similar operation by in columns of y of size scan_block[2]. Note this is done with the x/row wise 1/f map subtracted already.

If scan_first = 'yy' the order of row and column wise operations is reversed. Generally you want to analyse the scan direction with strongest noise features first if doing both.

Value

`image_fix`	A 1/f zapped version of the input image.
`row_map`	The row wise (x block) 1/f map.
`col_map`	The column wise (y block) 1/f map.

Author(s)

Aaron Robotham

Examples

image = Rfits_read_image(system.file("extdata", 'VIKING/mystery_VIKING_Z.fits',
  package="ProFound"))$imDat
temp_fix = profoundSkyScan(image)
magimage(image)
magimage(temp_fix$image_fix)
magimage(temp_fix$row_map)
magimage(temp_fix$col_map)

asgr/ProFound documentation built on Feb. 10, 2024, 9:04 p.m.