Align_image_stack is usually the best option other than possibly attempting it manually directly in Hugin.
On Sat, Feb 4, 2017 at 8:57 PM Casey Connor wrote:

Hi - I was curious what the best overall image alignment plugin/method in GIMP (or out of GIMP) was these days?

"Best" for me means "most powerful/flexible/option-rich".

I've come across the hugin align_image_stack, the G'MIC plugin's "Align layers" option, and the image registration plugin . (I've also used the "Exact
Aligner" script, but it's two layers only.)

The goal is to align and then use mean/median for noise reduction stacking. I'll probably be working in 16bit.

Do all three methods do sub-pixel alignment? I read someone on pixls.us suggesting that the user upscale the source images by up to 1.33x before aligning for the sake of effectively achieving sub-pixel alignment, but if the current alignment methods do that anyway, seems like I should skip it... ?

Thanks!

-c

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Pat David
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Align_image_stack is usually the best option other than possibly attempting
it manually directly in Hugin.
On Sat, Feb 4, 2017 at 8:57 PM Casey Connor

wrote:

I tried align_image_stack many times, using different options combinations, but coudn't get aligned images in the end. I'm trying to abandon PS and fully use gnu software, but, so far, couldn't find a decent replacent for PS's autoalign feature. The point is that I didn't use tripod, so there are alignment differences in the original frames. PS's autoalign can handle that situation in a very satisfactory manner. Am I missing something?
I don't want to piggyback Casey's post, but since I have the same question, I choose to put this post here. If admins feel I should open another thread, just let me know.

Per recommendations here, I've used it and it worked really well; I've read, and experienced, that it seems to need images to be pretty close

Thanks for the feedback.
I believe if I shoot with a tripod it would work fine. The point is that a tripod isn't an option to me most of the time. My only camera is an old point & shoot Canon A3100, boosted by CHDK. CHDK has many wonderful features, but the one I mostly use is its raw capability, not available on Canon original firmware. Besides, I usually do a lot of stacking, pushing the final image quality to its limits. And here is my problem.
With PS, I can auto align hand held shots with excellent results. The differences in perspective between shots do exist but are not big, because I try to hold the camera the most steadier I can when shooting. I just came from aligning the same set of pictures in PS I tried in Hugin, and it worked almost perfectly. Before that, I had also tried using JImage (and its full package FiJi), but it is really, really complex and I gave up. So, unfortunately (being an open source fan), I will still have to keep with PS, until I find an open source alternative to its auto alignment feature.

Did you try the -g option with align_image_stack? Or -t?

I align hand-held images with align_image_stack and it works fine, even
without those options... e.g. this one: https://www.flickr.com/photos/lacinato/32628735771/in/dateposted-public/

-c

Tried

align_image_stack -a *.tif

and

align_image_stack -a -g *.tif

and no success...

Tried

align_image_stack -a *.tif

and

align_image_stack -a -g *.tif

and no success...

The whole process:

1 - Shoot in DNG 2 - RawTherappe - Open dng's with preset Neutral and save them as tif 3 - align_image_stack.

Btw, beautiful image.

So, backing up a step: when you say align_image_stack doesn't work, what
do you mean exactly? I assumed you meant that it did a poor job aligning
the images,

Correct assumption,

but I don't think the command lines you list there would

even work to start the program, so I'm wondering now if you meant that it doesn't even run?

"-a" requires a prefix following it, and "-g" requires a number.

E.g.:

align_image_stack -a someprefix -g 8 *.tif

Documentation is here: http://wiki.panotools.org/Align_image_stack

Well, it works.

-a without explicit prefix defaults to the name of the first image file given.

-g without explicit number defaults to 5 (that is written in the --help option)

Btw, what os are you using?

I'm running this on Linux (Ubuntu 16.04)

Ah, ok. So what exactly goes wrong: one or two of the images is off-kilter?

Yes, that's it. I'm just checking the first two images, since PS successfully aligned all of them.

If you specify -g, try using something besides the default, as I'm not sure that using the default will change the behavior. (Meaning, not specifying -g probably results in the same thing as just "-g" -- the documentation is a little unclear, but I assume it's active when not specified.) Perhaps try -g 3 or 4 instead? I'm not 100% sure how to interpret it. If that doesn't work, try 6 or 7? Kubuntu 16.10.

-c

I tried

align_image_stack -a align -g 10 -t 5 *.tif

and

align_image_stack -a -dixyz *.tif

and

align_image_stack -a align -SAP *.tif

and the images (the first two) are still unaligned

The resulting stack by using Photoshop can be seen here https://flic.kr/p/SDKdBf

Did you try with a lower-than-default -g? E.g. "-g 3"?

If you want to upload the base .tif files somewhere, I can try to align
them, so we can see if there is some strange difference between align_image_stack on our machines.

-c

Hey, thanks for that!

Follows Flickr album https://flic.kr/s/aHskT2xjh1

Hey, thanks for that!

Follows Flickr album https://flic.kr/s/aHskT2xjh1

EDIT: I noticed that Flickr automatically changed the tiffs I uploaded into jpgs, so I wanted to make sure it wouldn't be a waste of time to you. I did what I suppose you'll do:
1 - Downloaded Flickr album
2 - Aligned the images with align_image_stack 3 - Opened the output from previous step as layers in Gimp. 4 - Changed layers opacity according to the mean rule (100%, 50%, 33%...) 4 - Did the same on PS

Conclusion: The format change didn't interfere in the original alignment issue: PS correctly auto-aligned the layers, but align_image_stack didn't.

The following images are screen shots from both ps and gimp showing the final stacks: http://imgur.com/a/drKdB

Ok -- I believe PS is beating align_image_stack because the picture seems to have been taken with a very wide lens (i.e. short focal length)
from close up... as a result, there is a lot of barrel distortion, and in addition there is a lot of camera movement between frames, so the result is that the image distorts differently from frame to frame and align_image_stack is not able to do it automatically. Meaning, when you
turn the camera that much, it "bends" the contents of the image in various different ways that make the images much harder to align. PS might be able to automatically correct for that distortion, but align_image_stack seems to struggle with it -- I get the same bad alignment results you did, but read on for more ideas:

Yeah, I suspect it had to do with the lens distortion, but, in this specific photo, I couldn't have place myself more distant because that was a corridor.

If you can use a longer focal length and stand farther away, and also hold the camera more still, I think it will work better (and have less barrel distortion as well.) Your PS screenshot also looks like there was
some kind of contrast or something applied (by PS, I assume? -- maybe related to the layer overlay mode when you stack the frames? -- or maybe
PS is just doing a better job!)

The only thing I did was applying the input script open stack or something like that (can't remember at this point its name) and changing the opacity. You're probably right assuming PS did some ajustments, because it probably calls Camera Raw under the hoods when opening the raw files, and by default, Camera Raw uses to open with some default settings already applied.

But note this: you don't have to, and probably shouldn't, use the manual
layer stacking method. That creates a simple averaging of the pixels, and it's probably pretty tedious to set up. There is another utility you
can use to create the median, instead of the average (aka mean), of the
image, which usually looks better. After I do align_image_stack, I use gmic to take the median of the files. The command line
looks like this (where test0001.tif etc are the images after alignment):

gmic -median_files test\*.tif -o output.tif

(you have to use "\*" with wildcards in gmic for whatever reason.)

I have tried the median method but, somehow, I generally prefer the median. As for the process being tedious, you're right, it is, although there is a much simpler way of doing exactly the same thing in PS, just by changing all the layers into Smart Object. Then you can apply in a single click the various stacking modes (including, of course, mean and median). Anyway, I'll give gmic a try.

Then I take the resulting output.tif file, open it in gimp, change the precision to 8 or 16bit, and remove the alpha channel (right-click the layer). This is the result of that process: http://caseyconnor.org/pub/image/aligned_and_medianed.tif

It certainly looks very good!
However, it's not clear after all, if you used gmic after align_stack or just applied it directly to the original frames.

I think it looks pretty good -- maybe not as nice as photoshop, but that
may just be the "contrast" that PS seems to have added. Note how the median, as opposed to the mean, eliminates the most mis-aligned frames automatically: those bad frames are left in if you average/mean the frames. As mentioned, I think you can make it look a lot better by taking better original pictures.

Even if you use PS to align the images, you should look into using gmic
to take the median, rather than stacking the layers. Just remember that
gmic outputs 32bit-float RGBA images, and you'll usually want/need to convert those to something more common.

(Note: current stable releases of gimp don't support high-precision images -- not sure if they will open the 32bit out of gmic or not. I'm using 2.9.5.)

-c

I'm using the latest developing version, 2.9.something, and it already supports, at least, 16-bit images. Not sure about 32-bit.

I feel like the open source tools are getting close to PS, regarding the stacking process. As for the rest, RawTherapee is really an option, and maybe Gimp sooner.

One last thought: if you are going to remove the barrel distortion in those images, you might try removing it before doing the image alignment... that might allow align_image_stack to work better... -c

That's a good idea, I'll try that.

Besides, many thanks for your patience and willingness to help.

I hope soon Gimp will present us a new alignment algorithm so we can forget, forever and ever, closed source apps.

Best wishes!

Could I have another link to the images to test something?

On Mon, Mar 27, 2017 at 12:59 PM oneaty wrote:

One last thought: if you are going to remove the barrel distortion in those images, you might try removing it before doing the image alignment... that might allow align_image_stack to work better... -c

That's a good idea, I'll try that.

Besides, many thanks for your patience and willingness to help.

I hope soon Gimp will present us a new alignment algorithm so we can forget,
forever and ever, closed source apps.

Best wishes!

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Could I have another link to the images to test something?

Sure.

https://goo.gl/photos/GCoSg4uANxLGunDAA

align_image_stack.exe -v -m -d -i -x -y -z -a aligned_ *.tif

Gave me pretty rock solid results with your .tif files:

https://transfer.sh/DgimG/oneaty.zip

pat

On Tue, Mar 28, 2017 at 3:03 PM oneaty wrote:

Could I have another link to the images to test something?

Sure.

https://goo.gl/photos/GCoSg4uANxLGunDAA

-- oneaty (via www.gimpusers.com/forums)

align_image_stack.exe -v -m -d -i -x -y -z -a aligned_ *.tif

Gave me pretty rock solid results with your .tif files:

https://transfer.sh/DgimG/oneaty.zip

pat Sure.

https://goo.gl/photos/GCoSg4uANxLGunDAA

-- oneaty (via www.gimpusers.com/forums)

Great!

I did a test with three new hand-held shots, and it worked perfectly.

So, by looking at the help text, it seems that you used all the options suited to focus stacking.

Maybe it should simply state that those are options suited for standard stacking. (Am I wrong to generalize it this way?)

Thank you very much Pat and Casey for your kind help.

PS.: I was preparing myself to meet Pat himself in Rio and thank him personally, but then I heard that he wouldn't attend the Conference... :)