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Merging layers with blends (startrails) causing checkered banding

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Theodore Lawrence
Merging layers with blends (startrails) causing checkered banding
on Aug 15, 2016 at 4:23:38 am
Last Edited By Theodore Lawrence on Aug 15, 2016 at 4:29:27 am

Apologies if this is a completely stupid question (I certainly feel like it is). I have been trying to find a way to properly merge the layers on a star trail photo for quite a while now an nothing seems to work (flatten image, merge layers, create snapshot, etc.). Saving the image results in similar issues when saving as jpg or tiff (no layers) - anything else seems to go over the 2 gig limit on file size so I can't even experiment with tiff including layers.

What idiocy has caught me here? I am using tiff files created from the DNGs to create the composite and simply applying a "lighten" filter to get the star trails to appear - no fancy jiggery pokery. Linked (in regrettable low res due to file size limitations) is a jpg export and a zoomed in screencap of the unmerged/uncompressed file to show the file without banding and with banding (it's zoomed in on the screencap to emphasize the dark areas where the banding occurs.). Perhaps working with jpgs as layers is better than tiffs? I don't know, feeling so dumb.

Thanks in advance for the advice!
SCREENCAP


EXPORTED FILE


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Kalle Kannisto
Re: Merging layers with blends (startrails) causing checkered banding
on Aug 15, 2016 at 9:08:38 am

My suspicion is that it has something to do with the layers being smart objects rather than images. This forces Photoshop to rasterize them upon export or flattening. I would bring the sequence in as images rather than smart objects.

Kalleheikki Kannisto
Senior Graphic Designer


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Theodore Lawrence
Re: Merging layers with blends (startrails) causing checkered banding
on Aug 15, 2016 at 4:44:23 pm

Gave it a try using FILE-->SCRIPTS-->LOAD FILES INTO STACK (which appears to layer the images without turning them into smart objects as dragging/dropping does) and there's still aberration.


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Kalle Kannisto
Re: Merging layers with blends (startrails) causing checkered banding
on Aug 16, 2016 at 2:56:43 pm
Last Edited By Kalle Kannisto on Aug 16, 2016 at 2:59:50 pm

That's mysterious. Can you curve a single image way lighter to see it the problem exists in a single image, and then try the same with an adjustment layer with curves on the layered file to see if the issue is already there before flattening/export but somehow not as visible before export?

Kalleheikki Kannisto
Senior Graphic Designer


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Theodore Lawrence
Re: Merging layers with blends (startrails) causing checkered banding
on Aug 17, 2016 at 9:12:09 pm

Curves doesn't appear to offer any significant clues either... You can just BARELY see some of the banding beginning in the trees I think if that gives us something to work with





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Kalle Kannisto
Re: Merging layers with blends (startrails) causing checkered banding
on Aug 21, 2016 at 3:22:03 pm

What is the "transform current layer" step in your action? That seems like more of a clue as to what might be happening here.

Kalleheikki Kannisto
Senior Graphic Designer


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Theodore Lawrence
Re: Merging layers with blends (startrails) causing checkered banding
on Aug 21, 2016 at 3:34:09 pm

The basic rundown(s) are as follows. Every option seems to yield the same results. I've dealt with it somewhat on the final product by applying a selective burn (midtones, shadows ~10%) but would like a more optimal solution.

1) import image series using LOAD FILES INTO STACK or dragging/dropping the files as smart objects.

2) Apply a blend to each layer - LIGHTEN - which creates the screenshot without banding.

3) merge layers with snapshot (CRTL+ALT+SHIFT+E), "merge layers", "flatten image", "merge visible layers", saving the image as a jpg or layerless tiff.


Images were shot on a Panasonic GH4 which is less than optimal for astrophotos but this doesn't APPEAR to be an in-camera issue


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Kalle Kannisto
Re: Merging layers with blends (startrails) causing checkered banding
on Aug 22, 2016 at 8:49:06 am

It would seem to me that the only way this can happen is if photoshop modifies the original files by rasterizing or rotating them. Do you have the "try to automatically align layers" active when you open as an image stack?

If the originals are DNGs, perhaps you should try opening them at 16 bits instead of 8? And turning the file to 8 bits (if need be) as the final step after flattening.

Kalleheikki Kannisto
Senior Graphic Designer


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