RE: Data Disk Format

["Creager, Robert S" <CreagRS@LOUISVILLE.STORTEK.COM>]

Tom,

I must disagree with you about where the problem lies.  Raw-to-fits is
adding in a BZERO of 32768 and a BSCALE of 1 to the fits header for the MARK
IV images.  What this says is take each pixel value as stored in the data
portion of the image, multiply by 1 and add 32768.  If this is not what was
intended, then the raw-to-fits program is incorrectly writing the fits
header.  Can you try DS9 on one of your dark files please?

I don't believe CFITSIO or FTOOLS are prone to errors like this, and I've
verified the CFITSIO routines I've written using FTOOLS.

The reason I chose
http://www.cv.nrao.edu/fits/data/samples/image/swp05569slg.fits for you to
look at, is it has a BSCALE of something other than 1 (.4)

Can someone using IRAF or some other package generate the mean/sigma of the
above fits file and maybe one of the MARK IV images, dark and star?  This
thread started between Tom and I when I questioned the sigma Tom was showing
for images.  For a dark frame - h3r1838.720, I generate 4161591 samples, sum
of 31829121594, mean of 7648, sigma of 716, while Tom calculates a mean of
~-25000 and a sigma of ~40.

CFITSIO and apparently DS9 give the following for the goofy image above:

sample count = 91410
sum = 88021501
mean = 963
sigma = 915

ImageScientist:
mean = -27103.4
sigma = 292.1

If I cannot convince you Tom with two programs (FTOOLS and DS9) agreeing,
then I gues we will agree to disagree :-)

Later,
Rob

> -----Original Message-----
> From: Tom Droege [mailto:tdroege@veriomail.com]
> Sent: Thursday, December 21, 2000 7:57 PM
> To: tass@listserv.wwa.com
> Subject: Data Disk Format
> 
> 
> Rob Creager has been having a problem reading the format on the Data 
> Reduction Group disks.  It is clearly an Intel/first 
> byte/last byte/signed 
> integer problem.
> 
> Have any of the rest of you had this problem?  Image 
> Scientist reads the 
> file as they are intended to be seen, but DS9 does not.  I am 
> not quite 
> sure what DS9 does, but it appears to rescale them in some 
> way.  Note that 
> these files are the output of the RawToFits program, so DS9 
> is reading 
> something in the fits header and doing the wrong thing.
> 
> I suspect that it is something trivial.  Since no one has complained 
> before.  Further some of you seem to be getting the same result as 
> I.  Possibly someone can tell me how to set up DS9 so that it 
> reads our 
> files as intended.
> 
> Note that the background for a dark frame (close to the 
> pedestal that is 
> set by the hardware) is around -25000 counts.  If you don't 
> see close to 
> this mean value for a dark frame, then you have this problem. 
>  Particularly 
> if you get a mean value of near +9000 instead of -25000
> 
> Tom Droege
> 
>