profoundMakeStack: Stack Images
In ProFound: Photometry Tools

Description Usage Arguments Details Value Author(s) See Also Examples

Stacks multiple images based on their signal-to-noise.

1 2	profoundMakeStack(image_list = NULL, sky_list = NULL, skyRMS_list = NULL, magzero_in = 0, magzero_out = 0, masking = 'and')

`image_list`	List; each list element is a numeric matrix representing the image to be stacked.
`sky_list`	List; each list element is a numeric matrix representing the sky to be subtracted.
`skyRMS_list`	List; each list element is a numeric matrix representing the sky-RMS to weight the stack with.
`magzero_in`	Numeric vector; the input mag-zero points. If length 1 then it is assumed all input frames have the same mag-zero point.
`magzero_out`	Numeric scalar; the output mag-zero point desired.
`masking`	Character scalar; what to do with masked pixels (NAs in the image). If 'or' a pixel is masked if any of the images being stacked have a masked pixel (NA in the image_list) at that location, if 'and' then a pixel is masked if all of the images being stacked have a masked pixel at that location.

The stack is actually done based on variance weighting. In pseudo code:

stack=0 stackRMS=0 for(i in 1:length(image_list)) stack=stack+(image_list[[i]]-sky_list[[i]])/(skyRMS_list[[i]]^2) sky_stack=sky_stack+(image_list[[i]]^2) stack=stack*sky_stack/(length(skyRMS_list)^2)

The output is explictly sky subtracted (so the sky is now 0 everywhere by definition as far as profoundProFound is concerned). The stacked sky is not returned. However, it can be computed by running profoundMakeStack again, but passing the sky list originally passed to the sky_list argument to the image_list argument instead, and not providing any input to the sky_list argument (or setting this to 0).

A list containing:

`image`	Numeric matrix; the variance-weighted sky-subtracted stacked image. Masked pixels are NA.
`skyRMS`	Numeric matrix/scalar; the sky RMS image/value of the final stacked image
`magzero`	The mag-zero point of the stacked image.

Aaron Robotham

profoundProFound

im1 = im2 = im3 =readFITS(system.file("extdata", 'VIKING/mystery_VIKING_Z.fits',
  package="ProFound"))$imDat

stack=profoundMakeStack(list(im1, im2, im3),
skyRMS_list = list(8,8,3))

#The new signal-to-noise weighted sky should equal sqrt(1/(1/8^2+1/8^2+1/3^2)) = 2.65

stack$skyRMS

# masking logic, here we have a wedding cake of masked regions:

im1[100:200,100:200]=NA; im2[120:180,120:180]=NA; im3[140:160,140:160]=NA

# masking='or' will conservatively mask any pixel that is masked in the stack:

magimage(profoundMakeStack(list(im1, im2, im3), masking='or')$image)

# masking='and' will optimistically only mask pixels masked in all stacked images:

magimage(profoundMakeStack(list(im1, im2, im3), masking='and')$image)