> Am Sonntag, 22. Juli 2018 23:35:30 UTC+2 schrieb clepsydrae:
>>
>> Thanks T. Modes -- align_image_stack does a great job of finding points 
>> but it appears that align_image_stack only matches pair-wise between 
>> sequential images, 1-2, 2-3, 3-4, 4-5, etc... Those image pairs are aligned 
>> very well, but I have 63 images in this stack so the error compounds too 
>> much from the first to the last, so it doesn't work overall.
>>
> Either they are aligned or not. So I don't know what you mean.
>

It's probably me who is confused, but: this is a stack of star field 
images, mostly overlapping. 1-2 aligns fine, 2-3 aligns fine, etc. 
Presumably there is a small error between each alignment though, so when I 
compare the alignment of 1-63 it has drifted, making the stack not useful 
for doing gmic median_image.

Maybe it is sufficient to connect all images sequentially and then run 
> align_image_stack only on the first and last image to connect them.
> (align_image_stack can only cope with a limited amount of movement. It 
> this is too big between first and last image you can do it e.g. to link 
> only every tenth image - connect images 0, 10, 20, 30, 40, 50 and 60)
>

Thanks -- I tried that (1-63 as well as connecting 1-7, 7-14, 14-21, etc, 
plus 2-62) -- it might have helped a little bit, but didn't really make a 
difference. The statistical pull of each immediate image connection seems 
too strong.

(I used the Fast Preview window to add these control points -- I assume 
that was your meaning.)

Do you think there is any way I can preprocess these underexposed images to 
be more usable with cpfind (so I can use them as proxy images for 
alignment)? As mentioned above, simple brightening did not work, and it 
doesn't seem likely that constrast enhancement will help since the stars 
are already pretty bright compared to the sky...

-- 
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