RE: [APML] Processing comet

[Glenn Ray <Glenn.Ray@aspentech.com>]

Hrvoje,

Welcome to the APML! 

Can you tell us what kind of film (brand, speed, expiration date) you used?
The red "mist" is often seen on films that are past their expiration and/or
have heat damage. 

Here is an extreme example:
http://www.geocities.com/glennlray/Astro/Aquila_Rising.jpg
This was a 3-minute exposure with Kodak PJ400 film that had not been
properly stored (too warm).  Unfortunately, I bought several rolls like it
and all showed this effect on long exposures (greater than 30 seconds).

The best way to reduce the effect is to edit the red channel only (not
deleting it) by adjusting the brightness and contrast settings, as well as
adjusting curves.  If you have Photoshop, you can select the Red channel to
edit and then click the "eye" on the RGB channel (lets you see all three
channels without actually editing it) so you can see the effect of your
changes.  

If you'd like more detailed help, feel free to e-mail me offline.

Glenn Ray
Cypress, Texas
www.geocities.com/glennlray/Astro
glenn.ray@aspentech.com



-----Original Message-----
From: Hrvoje Posilovic [mailto:hrvoje.posilovic@mail.inet.hr]
Sent: Thursday, April 18, 2002 9:22 AM
To: astro-photo@seds.org
Subject: [APML] Processing comet


	Dear APML List this is my first posting to the list, and first I
will like to apologize because of my bad english, but hope that you will
understand me.
For some time  reading yours discussions and looking beautiful images of the
sky. And so decided to try mysef, a couple weeks ago I photographed the
Ikeya-Zhang comet with 250 mm lens mounted on the small scope.
At the night of photographing there was a very thin red glowing cloud in the
front of the comet. And here starting my problems, after printing
photographs
there is terrible red "mist" all over the photography. The comet is very
bright and with long tail.I scanned the photo and tryed to remove red "mist"
in photoshop.First I completely deleted red channel and that significant
improve
 the image, but there is also some artifacts in blue and green channel. That
blue and green artifacts is impossible to remove without affecting comet
tail.
	I thinking about that problem and concluded following : the "mist"
pixels are randomly distributed in the image, but pixels that belong to the
comet tail are distributed in some linear trend. 
I wonder is it possible to separate randomly and linear trended pixels and
in similar way to clean the comet tail of the "mist".
	I will like to improve that image if is possible, becouse that is my
first image of the sky and I like it.

I will appreciate any  help.

Best Regards
Hrvoje Posilovic
from Croatia
 



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