ast4723_fits - 10/5/10 aka. AST 4723 FITS Format, Image...

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10/5/10 1 AST 4723 FITS Format, Image Viewers, Data Archives and Databases aka. .. The format of an astronomical image How to view an image Where to get images Astronomical Image Format FITS (Flexible Image Transfer System) is the standard Designed speci±cally to store scienti±c data sets Not interchangeable with image formats like JPG, GIF! Basic elements of a FITS image: Consists of 1 or more Header + Data Units (HDUs) Each HDU is called an extension Header Keywords at the beginning of the ±le that contain image information (date, telescope, ±lter, processing info, etc) Each keyword can be up to 8 letters long Data Units 3 types of data units Image (multidimensional pixel array) ASCII Table (rows,columns of data in ascii format) Binary Table (rows, columns of data in binary format) Astronomical Image Format FITS (Flexible Image Transfer System) is the standard De±ned at http://±ts.gsfc.nasa.gov/±ts_standard.html 130 page de±nition document de±ning valid ±ts ±les Header lengths and format Max dimensions for data arrays World coordinate systems Etc…
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10/5/10 2 Example FITS Header SIMPLE = T / conforms to FITS standard BITPIX = 8 / array data type NAXIS = 0 / number of array dimensions EXTEND = T ORIGIN = 'NOAO-IRAF FITS Image Kernel July 2003' / FITS ±le originator IRAF-TLM= '14:55:27 (18/04/2006)' / Time of last modi±cation NEXTEND = 3 / Number of standard extensions DATE = '2006-04-18T14:55:27' / date this ±le was written (yyyy-mm-dd) FILENAME= 'ALL_drz.±ts' / name of ±le FILETYPE= 'SCI ' / type of data found in data ±le TELESCOP= 'HST' / telescope used to acquire data INSTRUME= 'ACS ' / identi±er for instrument used to acquire data EQUINOX = 2000.0 / equinox of celestial coord. system / TARGET INFORMATION TARGNAME= '1315.5.16 ' / proposer's target name RA_TARG = 2.195397500000E+02 / right ascension of the target (deg) (J2000) DEC_TARG= 3.423866666667E+01 / declination of the target (deg) (J2000) FITS Image Extension Properties of the image extension Typically 1D or 2D, but can be multidimensional if representing a data cube FITS format supports a range of numerical data types
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ast4723_fits - 10/5/10 aka. AST 4723 FITS Format, Image...

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