[APML] Stacking [was: A Curves Exercise]

[Matt BenDaniel <matt@starmatt.com>]

Alan,

Firstly, I highly recommend RegiStar for registration. It is easier, faster and more accurate than PW (for images that contain field stars), especially when the images have different scales, rotations and warpage.
http://www.aurigaimaging.com/

Secondly, have you read DLC's paper on stacking?
http://www.dl-c.com/astro.pdf

Stacking can be a very complex subject, as there are multiple reasons for stacking (e.g. increasing S/N, mosaicking, chart overlay, correcting chromatic aberration),  and vignetting can be a tough problem. If I can reasonably combine the images in RegiStar, I'll do so. It's nice when it's that simple.

However sometimes the source images need AV or have skewed overlaps. In those cases, after registering with RegiStar, I bring the images into Photoshop and deal with them there. That can be a lot of work. I often end up with many layers to facilitate all that. The M33 that I recently posted here (http://starmatt.com/gallery/astro/m33.html) is an example. The two composite images were taken on different nights, at different image scales and different depths; they were skewed and both had vignetting. RegiStar did a great job as usual, but 95% of the work was in PS. Part of the result was from both images, but three corners were only covered by one of the source images. Making the blend between them required careful curving, AV, dust cleanup, and a custom mask for combination. It would require several chapters of a book to cover all that. I wonder if Jerry's book will.

Matt

At 08:52 05-12-02 -0800, Alan Voetsch wrote:
>I'd like to know how to
>stack two scans in PW and get that stacked image into
>PS. Or, should I manipulate in PS first, then stack in
>PW? What is the stack function in PW called?
>
>Alan  

--
Matt BenDaniel
matt@starmatt.com
http://starmatt.com


--  APML Archives at <http://astro.umsystem.edu/apml/>  ---
             Unsubscribe at <majordomo@seds.org>