First, I have no experience with stacking images of stars. But . . .
It sounds like the first image is extremely different from the last image,
so I'm thinking align_image_stack will not really work (Bruno or others can
say for sure.) Are you trying to make an image of a particular star or
group of stars? In either case, using all 1000 images, the area of interest
(in common to all images) is presumably a small portion of any one image
and this area of interest needs to appear in all 1000 images. I assume you
might want to partially *add* the images rather than just average them? Or
do you just want to enfuse them to remove noise and enhance saturation? Did
you take any dark slides? (I'm probably a bit out of my depth on these last
questions.)
A way around the limitation (my assumption) of align_image_stack might be
to break the images into sequential groups of say 25 or 50 (0-49, 50-99,
etc) and use align_image_stack on each group (the program should be able to
handle the much smaller stacking differences in each group.) Then you
can process each group separately. Finally you can take the sharper clearer
processed stacks and process them together. I think this would be just as
fast (or faster) and just as easily automated You might need to do some
manual cropping and/or process use cpfind rather than align_image_stack on
the second set.
Another possibility is to make interleaved stacks (0-49, 24-74, 50-99, etc.
Maybe the best thing would be to look at similar OSS that is specifically
designed for this. It's probably already solved all these problems and has
been optimized for the task. I don't remember the name of the software, but
I know it exists. I'm sure Google will be helpful ;-)
Let us know about what you do,
John
On Sunday, August 26, 2012 6:16:15 PM UTC-5, B. Schnieders wrote:
Hi all,
I need your help aligning some images :) I have a sequence of 1000 night
sky images taken with just a tripod, so alignment is needed before
averaging them.
The align_image_stack workflow does not seem to work properly for me -
the resulting images are aligned, but not very accurately, so that
averaging them results in a blurry mess.
Checking what went wrong, it seemed that align_image_stack did not find
2 control points for each consecutive pair of images, but keeps on
stacking photos. When adding proper points, the result is better, but
far from acceptable.
Another issue was the seemingly added-up error - I manually placed
control points between the first and last image, which seemed to lower
the blur by about 50%.
Now, manual work is acceptable for smaller image sets, but I wished to
fully automate the process for the full 1000 picture series. Thus, a
couple of questions:
- What would be appropriate settings for align_image_stack to detect
more/better control points? I already use -s 0.
- Can I tell align_image_stack to search for control points between all
combinations of images? I know this will take a while
- What settings would be needed that align_image_stack can detect
control points that move about half of the image's width?
Concerning the latter two points, I might rather use cpfind -
unfortunately, I have not yet figured out a way to let cpfind find any
control points on stars.
- What would be appropriate settings for cpfind to detect control points
on pictures of stars? I already tried to use --fullscale.
- Can I easily use either cpfind or align_image_stack from a script to
create control points in a pyramid-like manner (meaning, between
0-1-2-3-4..., 0-2-4-6..., 0-4-8-12..., 0-8-16-24,.) (to minimize
added up error and to keep CP count comparatively low)
- Can I force align_image_stack or cpfind to connect each image to the
rest with at least 3-4 good control points, or die?
So far for now, happy to hear any recommendations :)
Thank you,
Benjamin
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