Stray Light (Flare) Documentation

Flexible Image Transport System (FITS) Files

Stray light (flare) documentation pages

Introduction: Intro to stray light testing and normalized stray lightOutputs from Imatest stray light analysis | History

Background: Examples of stray lightRoot Causes | Test overview | Test factors | Test ConsiderationsGlossary

Calculations: Metric image calculationsNormalization methodsLight source mask methods

Instructions: High-level Imatest analysis instructions (Master and IT) | Computing normalized stray light with Imatest | Motorized Gimbal instructions

Settings: Settings list and INI keys/values | Configuration file input


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Flexible Image Transport System (FITS) is a file format designed for the archival transport and storing of scientific data [1, 2, 3]. The FITS standard [4] is developed by the International Astronomical Union (IAU) FITS Working Group [5]. It may contain multi-dimensional arrays (1D vectors, 2D images, 3D+ data cubes), tables containing information, headers to provide descriptive information about the data, and supports compression of the aforementioned data.

Interacting with FITS Files

The FITS file format is commonly used within the astronomy community; therefore, many software tools/applications already exist for analyzing FITS file image data.


NASA GSFC maintains a list of FITS viewers [6].


SAOImageDS9 [7, 8] is one example of a commonly-used, free FITS file-viewing application. SAOImageDS9 is used by amateur and professional astronomers alike, for analyzing scientific image data such as from the James Webb Space Telescope (JWST).

A screenshot of the SAOImageDS9 application. A stray light metric image FITS file has been manipulated with logarithmic scaling and the “b” colormap to better reveal certain stray light artifacts.

I/O Libraries 

NASA GSFC maintains a list of FITS I/O Libraries that work with many common programming languages [9].





[4] FITS Standard Document.

[5] IAU FITS Working Group.

[6] FITS Image Software Packages.

[7] Joye, W. A., & Mandel, E. (2003). New features of SAOImage DS9. In Astronomical data analysis software and systems XII (Vol. 295, p. 489).

[8] SAOImageDS9.

[9] FITS I/O Libraries.