RE: correct bias usage and using "Search the TASS Site"

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

Arne,

I would never accuse you of being dense any day, but I have been accused of
obfuscating the obvious regularly.

Column 3 was once determined to be a good covered column, as it varied
little between exposures of the same length.  Typically, I see variances
between column 3 of less than 20 ADU (between dark/object), so this was
chosen (by folks before me, I just verified/used it) as a 'scaling' column
to offset small timing irregularities.

"min central mean" is the minimum value of the group of means of the central
box from each image.  A way of making sure  "box mean" is the actual mean of
the central box.  I hope I un-obfuscated that enough.  The min central
mean/box mean is a scaling factor so the images play in the same average
space. 

I just realized when reading your comments (and then re-reading AIP), that
the bias is only(?) required when using dis-similar image integration times
(dark vs object) to be able to generate a scaled dark/thermal image.  If
this is true, then you can ignore my first question.


> -----Original Message-----
> From: aah@nofs.navy.mil [mailto:aah@nofs.navy.mil]
> Sent: Friday, August 03, 2001 12:08 PM
> To: tass@listserv.wwa.com
> Subject: Re: correct bias usage and using "Search the TASS Site"
> 
> 
> Rob,
>   I must be particularly dense today; I can't follow your logic.
> Why column 3?  What is (min central mean / box mean)?
>   As long as exposures are the same length as the darks, you
> can just subtract mean dark from each exposure rather than
> (mean dark - mean bias).  It is one less subtraction and
> actually improves the signal/noise.
> Arne
>