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

["Scott Hammonds" <shammonds@creatorsview.com>]

Extraordinary Wei-Hao!  

Scott Hammonds



-----Original Message-----
From: Wei-Hao Wang [mailto:whwang@gmail.com] 
Sent: Monday, July 05, 2004 4:12 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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