	Sloan Digital Sky Survey

JPEG WCS Header

Adding WCS info to JPEG images.

Tools such as rdjpgcom allow one to read comments from JPEG files. The tool wrjpgcom allows one to write comments to a JPEG file. We propose to use this comment block to add some WCS info to the SDSS JPEG images provided by SkyServer and the ImgCutOut Service.

Technicalities

We feel the simplest approach is to put the FITS keywords in the comment block. Adding the comment is easy on Linux ..

 >wrjpgcom -cfile sample.txt sample.jpeg > commented.jpg

And here is the file to look at.
Getting the info back is also easy ...

>rdjpgcom commented.jpg

Author="SDSS Collaboration "
Info="http://skyservice.jhu.edu/develop/jpeghead/index.html"
TITLE="SDSS Image Filter u"
SIMPLE=T
CRPIX1=744.5
CRPIX2=1024.5
CRTYPE1='RA--TAN'
CRTYPE2='DEC--TAN'
CRVAL1=179.948240689264
CRVAL2=0.101381194295879
CD1_1=-3.8008997158114E-08
CD1_2=0.000109924630958157
CD2_1=0.000110062460780114
CD2_2=-4.78845056498477E-08
NAXIS=2
NAXIS1=2048
NAXIS2=1489
EPOCH=2000

Above then are the keywords we intend to put in the JPEG.
Of course ANY fits keywords could be added.

EXIF

Looked into using proper EXIF tags for this but it is messy and the comment block seems like the simplest approach. We tried to contact ADOBE to reserve a bunch of numbers but the mail bounced.

William O'Mullane
Last Modified :Wednesday, August 6, 2003 at 2:34:59 PM , $Revision 1.1 $