RE: [APML] Scorpius, Sagittarius, and the Milky Way

["Chris Schur" <cschur@therim.com>]

Wei-Hao,

A truly dramatic image, such tiny stars!  Reminds me of a schmidt camera.
That film seems remarkably balanced in color, albeit a bit slow.  Nice rich
reds and very neutral Milkyway fields.  I like the Norma nebula at the
bottom.

Chris

-----Original Message-----
From: astro-photo-bounces@seds.org
[mailto:astro-photo-bounces@seds.org]On Behalf Of Wei-Hao Wang
Sent: Monday, July 05, 2004 1:12 AM
To: APML
Subject: [APML] Scorpius, Sagittarius, and the Milky Way


ALOHA,

A new image is in
http://www.ifa.hawaii.edu/~wang/gallery/picutres/sco_sgi_milkyway.htm

To correct the vignetting pattern, I used a little crappy but quick
flat field method.

As I introduced my flat field technique to you about half year ago, I
took several
images of daytime sky and average them to make a flat image.  The old way is
to nonlinearly match this flat with the sky background in a real
astronomical image
and then divide the image with the matched flat image.  This method works
quite
well.  I had showed the results on my Orion mosaic to you.  However,
this technique
may be a little difficult for most people since it requires some computer
programming.

In order to see if things could be more simple, I divide the image with the
flat
directly (without any background matching).  The result is the image above.
I have to say, this flat fielding is not perfect but the residual
vignettign pattern
can be so easily fixed in PhotoShop.  I think this is worth trying.
You don't need
to write a C++ program.  All you need is to take a picture of daytime sky
and
find a image processing software that does division (PhotoShop doesn't).

Cheers,

Wei-Hao

--
________________________________________________________________
Wei-Hao Wang  :)

Institute for Astronomy at University of Hawaii

Address:
2680 Woodlawn Drive         Personal Website:
Honolulu, HI 96822             http://www.ifa.hawaii.edu/~wang
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