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About ROB Image Reductions

Descriptions of how image reductions are done on data from the ROB telescope


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Contents

Overview
Master Images
 - Utility Routines
 - masterCreate.pl
 - darkCreate
 - flatCreate
Processing Object Imges
Astrometry
Photometry
Welch Statistics

Overview

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I'm generally unhappy with the values that my reduction pipeline is producing. This page will document what I'm doing and allow others to look at what I've developed. Also I tend to find my own problems when I look closely and document my work. All image calculations presented below have been verified with FTOOLS and AIP4Win as appropriate. All fits file interactions are accomplished with CFITSIO and Astro::FITS::CFITSIO.

Master Images

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The first step in the reductions is to create master dark and flat images. A perl script called masterCreate.pl analyzes the available dark images and feeds the image list to darkCreate to munge into an appropriate image. The same happens for flat images using flatCreate, except star images are used as I currently have no ability to take true flat images.

Utility Routines

A utility tool I use to calculate image statistics called 'stdimg' was checked against 'fimgstat'. An image was chosen at random and the data given by stdimg 3050/V_flat.fits was compared against fimgstat 3050/V_flat.fits INDEF INDEF, and no differences were noted.

masterCreate.pl

Image selection stuff.

darkCreate

Using fimgcreate 16 "2064,2034" "none" zero.fits, an image of appripriate size was created filled with 0's. Then, five more images were created using farith zero.fits 1 one.fits +, farith zero.fits 2 two.fits +, farith zero.fits 3 three.fits +, farith zero.fits 4 four.fits +, farith zero.fits 5 five.fits +.
  • First, three runs were executed using darkCreate, each using either the mean, median or IQM (Inner Quartile Mean) with the images one.fits, two.fits, three.fits and four.fits. fimgstat ?.fits INDEF INDEF was then executed on each of the images generated, which all produced min/max/mean values of 2.5, which is appropriate for the four images given.
  • Second, three runs were executed using darkCreate, each using either the mean, median or IQM with the images one.fits, two.fits, three.fits, four.fits and five.fits. The min/max/mean produced values of 3, 4 and 2.5 respectivly, which is wrong for median and IQM. The median problem was off by one image when an odd number of images was used. The IQM problem was not using the last image when there were an odd number of images.
Testing was done after darkCreate.c was fixed and the correct results were achived for both image sets (2.5 and 3) and all three methods (mean, median and IQM).

flatCreate

The program flatCreate.c suffered from the same problem as darkCreate.c, and the same fix was applied.

Processing Object Imges

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DAOPHOT options and FWHM usage.

Astrometry

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How matched against TYCHO-2.

Photometry

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Changed from an iterative Perl script to a GSL GSL C program.

Welch Statistics

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Algorithm used.

© Copyright 2004-2011 Robert Creager. All Rights Reserved.
tass/reduce.html last modified 14:22:22 07-Jun-2009