[AstroPy] An Odd Result on an All-Sky Image--Equal Images and Bars?

Wayne Watson sierra_mtnview at sbcglobal.net
Wed Apr 15 17:26:43 EDT 2009

(Well, I guess the moderator didn't release with two 1M fits files. I'm 
posting it without them. Jumping down to HERE might be best. The first part 
of this discusses the two files, but maybe it strikes a cord with some. The 
most important part might be about comparing two files. I'm attaching a 
small file of the barred image I discuss. I think if I keep it down to 40K, 
it'll pass through to the list. )

With help from posts above, I finally got a fits image from some old
data I was using for test purposes.  As displayed by the sentinel
software, the frame was dark with  the moon in the center a as small
bright circle. I used a program, ccdsoft*, which displays fits images.
It had much greater contrast. One could see the circular horizon, and
trees along the horizon, even my house in the lower right. Neighbor's
lights were visible in the lower left. That's not really anything new,
but why the difference in the two images as displayed, I asked myself? I
tried the image in DS9, and it showed it to be almost identical to the
image displayed by sentinel.

It's quite possible that ccdsoft has some auto contrast feature that was
applied, but I doubt it.  I saved the odd ccdsoft displayed image to a
fits file. The file name ends with ...x.fits. I'm pretty sure the pixel
values will be different from the other file. Is there a way to compare
the two easily? This is just curiosity.
Perhaps more importantly here, and this I had no immediate plans of
discussing here, since it was currently less important to putting in a
"save to fits" ability; how does one get rid of those vertical lines
(bars)? They are from the video camera working at high gain, I'm pretty
sure.  Dark frame subtraction doesn't help. Although removing the lines
is interesting here, it gets to be important in the situation where I've
stacked 256 images of the sky (which does show many stars--and noise).
BTW, the unstacked image is a  1/30th sec exposure. The purpose there is
to bring out dim stars. It works fine, but those lines probably won't
help star identification. I would think if it can be done with this
image, it could apply to the stacked images. Comments?

I'm attaching two fits files. Note that in the fitss file provided that
something of a coordinate system, 3 lines, is shown. That's pure
experimentation from some other interests.

Interestingly, in DS9, the image is upside down (neither file is the
display screen of the DS9).

* BTW, this is the first time these images have been available to
ccdsoft or ds9. ccdsoft does have IP capabilites, and sentinel has none.
As a consequence, they are seldom seen as provided by ccdsoft or any IP
program. Just playing around with a few IP controls on ccdsoft was
interesting.  That's a real plus having IP.

            Wayne Watson (Watson Adventures, Prop., Nevada City, CA)

              (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
               Obz Site:  39° 15' 7" N, 121° 2' 32" W, 2700 feet

            All the neutrons, and protons in the human body occupy
            a cube whose side is 5.52*10**-6 meters (tiny!). That
            adds up to a 150 pound person. It's not a surprise that
            we are mostly space. (Calculation by WTW)

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