ABIRL

A Basic Image Reduction Library

A. C. Boley, 15 Sept. 2021

ABIRL is a simple implementation of astropy and related libraries to reduce astronomical observations. It is also a work in progress, and this repo is to help me stay organized.

In python, load the library as normal:

:import ABIRL as ab

You can always type

:help(ab) to see your options

The following provides a list of the main tasks.

headerSearch

headerSearch(filelist, SEARCHKEY="OBJECT", SEARCHVAL="bias",NAMEONLY=False,LISTALL=False)

• Scans list of file names to display exposure times and object types from HDU header.
• Will also show all values in header itels if listall=True.
• NAMEONLY just prints the filename if a match exists.

addCoords

addCoords(fout,filelist,pxu=1e-3)

• Use to get approximate coords if you trust the plate scale. But be careful and check it.
• This is not an astrometric solution.
• pxu converts the pixelsize to the same units used for the platescale. Default assumes pixel is in um while platescale is mm/".
• fout is the prefix of the output files.

medianFilter

medianFilter(fout,filelist,BLOCKX=1,BLOCKY=1)

• Applies a median filter over the entire image in that it runs a window over the original data and replaces each pixel with the median for a window centred on that pixel.
• BLOCKY and BLOCKX control the size of the rectangular window (+/- BLOCK* from the centre pixel).
• fout is the prefix of the output files.

chunkQuartileFlatten

chunkQuartileFlatten(fout,filelist,BLOCKX=32,BLOCKY=32,SKIP=1)

• Subtract the median value from all pixels within a chunk of the image.
• The median value is based on a window of width 2 BLOCKX +1 and 2 BLOCKY +1.
• The setting SKIP sets the number of cells in each image chunk, which is used to speed things up.
• SKIP=1 does not use image chunks. Larger chunks are faster, but can create pixelation.
• But this is better than the deceptive pixelation that could be created by too small of BLOCKX and BLOCKY.
• Ultimately, this is for removing gradients in the images.
• fout is the prefix of the output files.

medianFlatten

medianFlatten(fout,filelist,BLOCKX=32,BLOCKY=32)

• Subtracts the median within a window from each pixel.
• The window is centred on the pixel of interest, with size 2 BLOCK* + 1.
• Careful of bright features, which can create image artefacts.
• The purpose is to flatten an image. If this is too slow, consider using chunkQuartileFlatten
• fout is the prefix of the output files.

chunkMedianSubtract

chunkMedianSubtract(fout,filelist,BLOCKY=16,BLOCKX=8)

• Super fast way to flatten an image by directly subtracting medians
• based on a supergrid set by BLOCKY and BLOCKX subdivisions of the
• image in X and Y, respectively. This can leave sudden jumps between
• regions of different brightnesses. If this is the case, consider chunkQuartileFlatten
• fout is the prefix of the output files.

addBase

addBase(fout,filelist,base=100)

• Sometimes it could be advantageous to add a flat background adu. Not standard.
• fout is the prefix of the output files.

subtractImg

subtractImg(fout, fitsToSubtract, filelist,catch=1)

• Subtracts one image from all images in a list.
• fout is the prefix of the output files.

divideImg

divideImg(fout, fitsDenominator, filelist)

• Divides all images in list by another image.
• fout is the prefix of the output files.

meanCombine

meanCombine(fout, filelist)

• Mean combine files in file list takes.
• fout is the prefix of the output files.

medianCombine

meanCombine(fout, filelist)

• Median combine files in file list.
• fout is the prefix of the output files.

skyMedianCombine

skyMedianCombine(fout, filelist)

• Median combine sky flat files in file list.
• Ensures normalization before combing, as exposure times vary
• fout is the prefix of the output files.

getMedian

getMedian(filename)

• Median of one file

simpleAperture

simpleAperture(fout,filelist,aperturelist)

• You need to first create an aperture list that contains the pixel X Y coordinates, the inner radius of the aperture, and the outer radius of the aperture.
• The filelist should have the same order as the aperture list.
• fout is the prefix of the output files.

getMags

getMags(fout,photlist,rad=0.0014)

• Get magnitudes for objects in aperture file and compare with Gaia catalogue.
• Requires apiEx and assumes images are astrometrically calibrated.
• photlist is the list of aperture files.
• fout is the prefix of the output files.

regionLengths

regionLengths(regionfile)

• get region width in arcseconds.
• Assumes ds9 regionfile output of a polygon.
• Units need to be in degrees for the region file

rollImage

rollImage(fout,fin,RISE,RUN)

• Roll the image following RISE and RUN in pixels.
• Used for aligning satellite streaks along columns or rows. Experimental.