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RE: [APML] Gradient and Vignette removal software



Title: Message
Jeff, the main cause with my 5.5 inch schmidt is a regular vignetting from too small a primary mirror.  the vignette is about 30 percent, and really comes up on deep shots.  My 8 inch schmidt has an over size primary and very litte vignetting. 
 
Chris Schur
 
-----Original Message-----
From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org]On Behalf Of Jeff Ball
Sent: Thursday, June 27, 2002 6:00 AM
To: astro-photo@seds.org
Subject: RE: [APML] Gradient and Vignette removal software

Yes, that is why I prefer Picture Window for the simple stuff like vignetting.  But Picture Window's multipoint can be used to construct a more complex gradient, but I have found this more difficult than Photoshop manual gradient construction as per Matt BenDaniel.  To be honest, I think it is very difficult to manipulate wide field images without altering the color/background that is truly there.  I have used the techniques discussed below, but I am not sure that I did more harm than good on some of the images.  Perhaps it is the manipulator rather than the manipulation technique that is the problem!  Best of luck Chris.  Please share your final results with us.  I can only imagine some of the issues a Scmidt camera may present with gradients.  
 
Chris, if you are still reading this, what are the gradients associated with, i.e. processing, sky glow, green pixels from aging film?  Thanks.
Jeff Ball 
-----Original Message-----
From: owner-astro-photo@seds.org [mailto:owner-astro-photo@seds.org] On Behalf Of Mike Unsold
Sent: Thursday, June 27, 2002 8:15 AM
To: astro-photo@seds.org
Subject: Re: [APML] Gradient and Vignette removal software

Geometric gradients can be generated using software and can work well but often a gradient is not a simple geometric shape. For this reason would it not be better to extract the background component from the original image since it would contain both the complex shape and color of the original gradient?
 
Mike