I have to Auto-Align Layers twice to make it work correctly

[Bob Somrak]

I was working on a problem and discovered this issue.  I have a PSD file.  I "Save As" the PSD file as a TIFF so they should be the same.  Put the TIFF on top of the PSD and chose Auto-Align and set the blending mode of the top Layer to Difference and got this.

I selected the layers AGAIN and chose Auto-Align AGAIN and this time it WORKED as I got this as the Difference.  A perfect match.

I tried this on a couple other photos and got the same results.  Seems like the Auto-Align doesn't EXACTLY align the first time you use it.

[Trevor.Dennis]

What options did you use when saving the TIFF file?  I would have expected that if you have compression set to None, it would save an identical version.

[D Fosse · Accepted solution]

If you use auto-align a lot, you will soon discover that the result is frequently offset by 4 or 5 pixels. Once nudged into position, the match is usually perfect - so it's not that the algorithm itself doesn't work. I'm willing to bet that's what happened here.

The offset appears random and can go either way, often diagonally, such as two pixels right and four up.

I've no idea why this happens, but I always factor that in. Once completed, I go to 100% and nudge into place. Only then do I run auto-blend if that's the next step.

This is also one reason I never use Photomerge.

[Bob Somrak]

D Fosse

I could understand if you were auto-alining two DIFFERENT tripod shots for instance but this is a RESAVE of the SAME photo and I expected it to be dead-on the first time.  I guess I will just have to do the Auto-Align twice from now on as that seems to work, at least in this occasion.  You would think an operation that is used a lot like ALIGNING would work better.

[D Fosse]

Yeah, but there's no guarantee it won't be offset the second time as well. It's totally random. Much better IMO to just check at 100% right away and be done with it.

I should stress again that the algorithm works. The match is perfect aside from the offset, so there's really no reason to run it twice.

[Bob Somrak]

I wouldn't say the algorithm works if it is OFFSET, especially in the scenario of an identical photo.  In my example above it should be considered a bug.  Why did it work the second time?  The algorithm should be working the same.

[D Fosse]

As I said, the offset is random. Happens this time, not the next.

Yes, I agree it's a bug. I just hasn't bothered me all that much, because I like to double check alignment in any case. There are many scenarios where you would want to nudge a pixel or two even if it did work as expected - for instance to compensate for parallax errors.

[Bob Somrak]

Now that I am aware of this problem and have been checking more it seems like it is BADLY unaligned MOST of the time on the first try but works well on the second try of auto-align.  My example in the original post is essentially the same photo and it can't even do that well.  Adobe needs to work on this.

[Bob Somrak]

I was doing some more layer alignments and this still appears to be broken.  You would think something as basic as aligning layers would work correctly after all these years, especially when one is a direct derivative of the first as my original post states.  POOR job.

[Trevor.Dennis]

Bob, I have tried this a few times just to test, and I am always getting a perfect result.  I use the Difference trick when stitching multiple panels of topo maps, and always do it manually, because of the small overlap.  So  I am not sure what to suggest.  You are right that you shouldn't need more than one go to Auto Align, and Dag appears to back up your experience that this is sometimes necessary.

[Bob Somrak]

Thank you Trevor for the reply.  I only did a couple stacks today the first time since a year ago and neither worked "perfect" the first time but did ok on the second try as I indicated above.   I will be doing several in the next few weeks so hopefully I will have the good luck you did.  I just decided to do the alignment twice every time to try to avoid the problem.  The photo that started the thread was a TIFF that was a derivative of the PSD that was essentially exactly the same.  I was doing this to try to help a user that was having issues with exports of PSD files in Lightroom on the Lr forum and that is how I discovered the issue. 

[Bob Somrak]

Trevor.Dennis  wrote

it would save an identical version.

The TIFF is identical as you can see from the second auto-align because the Difference blend is BLACK.  The problem is Auto-Align didn't work correctly the first time.

[AdamB82]

Any reason these bugs aren't being fixed and auto-align is just being left buggy?  Why does auto-align still not work at the end of 2021?  Is there any roadmap for updating auto-align to actually work for things like hand held images?  Microsoft ICE passed photoshop in auto aligning about 10 years ago, will Adobe try to compete again on this?

[enrique.leopard]

I am trying to align 24 images loaded as layers. They are 1920x1080 px. If i check Geometric Distortion Photoshop never finishes to process.  So I use only AUTO. After one pass layers are align very badly. After applying auto.align again the result is much better!  doing it a third time makes very small difference... Now it is december 2023 and i am using PS 25.3.1.   Wish this featue could be improoved. I do a lot of Longterm timelapse and use this to corret cameta movement.

[D Fosse]

Correct, the pixel alignment is often not perfect.

But don't run it again! It's just a clean pixel offset. Rerunning it gets you another round of resampling, and you don't want that.

Press ctrl+1 to get 100%, then use the arrow keys to nudge into position, one by one pixel.

I agree, this should be fixed. It's been reported here many times. But in the meantime, just nudge to get the best result.