Re: [TASS] Flat fielding

[Chris Albertson <chrisja@jps.net>]

Andrew Bennett wrote (in part):

> 1) Flatfielding by dividing by a vector derived from a
> single image is a waste of time and introduces errors.

> 2) One should instead use a flat vector derived from
> a large number of images.

With the Mk III "number of images" does not mean much.
It is "number of rows" that matter.  The camera supplies
an endless and unbroken series of scan lines.  The software
arbitrarily chops this continuos data stream up into "images".
An operator can tell the software to make the image files
any size he wants.  We choose a "standard" size simply
so that one image fits on a floppy disk.  When making camera
adjustments I routinely set the image size down to 200
scan lines.  Would it be better for me to average four
200 line images then use one 800 line image?

So when we "divide by a vector derived from a single image"
we are actually "dividing by a vector derived from 800
scan lines"  Maybe 800 is the wrong number and 400 or
3200 would be better?  I can send you a CD with raw images
on it. if you want to experiment.




--
   --Chris Albertson             home: chrisja@jps.net
     Redondo Beach, California   work: calbertson@logicon.com