MDIFF(1)

💖 MDIFF(1) — the mDiff page, but make it make sense 💖

okay so this is the mDiff manual, from the Montage crew (manual page MDIFF(1)), and bestie I need you to know up front: this one is niche and it's specific and it ate. It does ONE thing. It does it well. Let's go 🦋

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✨ NAME ✨

mDiff — Calculates the difference between a pair of overlapping images. That's it. That's the whole job. 💅

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✨ SYNOPSIS ✨

mDiff [-d level] [-n(o-areas)] [-s statusfile] in1.fits in2.fits
out.fits template.hdr

look at her go, all four positional args and everything 🌸

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✨ DESCRIPTION ✨

So mDiff calculates a simple difference between a single pair of overlapping images. Single pair. Not a whole pile. A pair. 🫶

This is meant for use on reprojected images where the pixels already line up exactly. No cap — if your pixels aren't already perfectly aligned, this is not the tool, bestie.

mDiff analyzes an image metadata table to determine a list of overlapping images. Each image is compared with every other image to determine all overlapping image pairs. 🔍 A pair of images are deemed to overlap if any pixel around the perimeter of one image falls within the boundary of the other image.

perimeter pixel in the other image's boundary = they're overlapping, periodt 💫

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✨ OPTIONS ✨

• -d level — Turns on debugging to the specified level (1-4). 1 to 4, and yes you have to pick one 🎀
• -n — No-area-images flag. Creates difference image without requiring pixel area FITS image. freedom from area images, iconic
• -z factor — Scale second image by factor before subtracting. multiply then subtract, the math girlies get it ✨
• -s statusfile — Output and errors are sent to statusfile instead of to stdout. redirect the whole vibe 📁

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✨ ARGUMENTS ✨

• in1.fits — First input FITS file. (Also needs area image in1_area.fits, or use -n flag) 🌸
• in2.fits — Second input FITS file. (Also needs area image in2_area.fits, or use -n flag) 🌸
• out.fits — Difference FITS image to be generated. this is the one you're making, the main character 👑
• template.hdr — FITS header template used to generate output image. the blueprint 🎀

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✨ RESULT ✨

FITS image and area image representing the difference in the overlap region. two for the price of one, we love a duo 💖

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✨ MESSAGES ✨

• OK — [struct stat="OK"] ✨
• ERROR — Cannot open status file: statusfile 💀
• ERROR — Images don't overlap 😭
• ERROR — All pixels are blank 🙈
• ERROR — Template file not found 🔍
• ERROR — FITS library error 💥
• ERROR — general error 🫠

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✨ EXAMPLES ✨

$ mDiff proj/in1.fits proj/in2.fits output/diff.fits template.hdr
       [struct stat="OK"]

and that's it, that's the whole run, slay 💅

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✨ BUGS ✨

heads up bestie, read this part, fr fr

• The drizzle algorithm has been implemented but has not been tested in this release. Not tested. In this release. We said what we said. 💀
• If a header template contains carriage returns (i.e., created/modified on a Windows machine), the cfitsio library will be unable to read it properly, resulting in the error: [struct stat="ERROR", status=207, msg="illegal character in keyword"] Windows line endings strike again 😭
• It is best for the background correction algorithms if the area described in the header template completely encloses all of the input images in their entirety. If parts of input images are "chopped off" by the header template, the background correction will be affected. We recommend you use an expanded header for the reprojection and background modeling steps, returning to the originally desired header size for the final coaddition. The default background matching assumes that there are no non-linear background variations in the individual images (and therefore in the overlap differences). If there is any uncertainty in this regard, it is safer to turn on the "level only" background matching (the -l flag in mBgModel).

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✨ COPYRIGHT ✨

2001-2015 California Institute of Technology, Pasadena, California 🌈

If your research uses Montage, please include the following acknowledgement: "This research made use of Montage. It is funded by the National Science Foundation under Grant Number ACI-1440620, and was previously funded by the National Aeronautics and Space Administration's Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of Technology." 🫶

The Montage distribution includes an adaptation of the MOPEX algorithm developed at the Spitzer Science Center. ⭐

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okay that's the whole page bestie, you're officially a mDiff girlie now 💅✨

this was Montage 5, dated Dec 2016 — thanks for reading, ily, go difference some images 🦋🎀