Why does Photoshop hang at "Align Selected Layers Based On Content" when auto-aligning many astrophotography stacks?
Asked 8/9/2016
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2 answers
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When I try to auto-align about 100 masked astrophotography stack images in Photoshop, the progress bar quickly reaches "Align Selected Layers Based On Content" and then appears frozen there for a very long time. Activity Monitor shows Photoshop still using 100% CPU.
System: Photoshop 2015.5 on a mid-2014 MacBook Pro Retina, internal and external SSD scratch disks with plenty of free space, and ample RAM assigned. I had completed similar astro stacks before without this issue.
After killing Photoshop and retrying a few times, the same file eventually worked. One possible variable is that I also use Parallels with GPU acceleration enabled, which may have been started after Photoshop in the failed attempts.
Is this likely a real Photoshop hang, or can the progress bar simply stop updating during auto-align? Could another app or VM competing for RAM/VRAM cause this behavior?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
3
For some unknown reason, I've decided to give it a third try after killing Photoshop again, and after a few minutes, it started working:
It's the exact same file on the exact same computer. I only have one suspect: I have Parallels installed that runs Windows (with GPU acceleration enabled) inside a VM (the VM has nothing to do with Photoshop or my photography, but they obviously share resources, especially RAM and VRAM). In the first tries, I may have opened Parallels while Photoshop was already running. Maybe it created some sort of memory/VRAM problem. This time, when I launched Photoshop, Paralells was already running. Maybe Parallels trying to allocate some resources made Photoshop go crazy, but in the last one, it had already allocated what it needs to Photoshop went stable. This is my only possible explanation.
Originally by user6411. Source · Licensed CC BY-SA 4.0
user6411
9y ago
0
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It may not be truly frozen if Photoshop is still using heavy CPU, but in your case the repeated stall at the same step suggests a resource/conflict issue rather than normal progress-bar behavior.
From the outcome you posted, the most likely culprit is contention from Parallels/its GPU acceleration. A VM can compete with Photoshop for RAM and especially VRAM, and that can make large auto-align jobs unstable or appear stuck. Since the exact same file later completed, the image data itself was probably not the problem.
Practical takeaway: for large layer-align jobs, close or avoid launching resource-heavy apps/VMs, especially anything using GPU acceleration, before starting Photoshop. If you must use both, launch them in a consistent order and keep as much RAM/VRAM free as possible. If Photoshop sits for hours at the same stage and never progresses, it’s reasonable to treat it as hung and retry under a cleaner system load.
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