What would be responsible for this? (a regular grid showed up in a stacked long exposure)

[turnstyle]

Hi all, I'm starting to dabble with stacking long exposures, here's something I made last night:

To make this, I:

1) Took 80 30 second exposures, with "long exposure noise reduction" off (if left on, the star trails become dotted)

2) Imported them into Lightroom, and applied the same adjustments to all of them: gave them all exactly the same white balance, some gradients, sharpening, etc..

3) Exported from Lightroom as full-size JPGs

4) Imported those into Pixelmator, stacked them as layers, and set the blending mode to "lighter", and saved a full-size JPG.

But then I noticed an odd grid, you should have no problem seeing it here:

Any ideas what might be responsible for that? And, I assume, no simple way to correct it?

Something actually in the RAW files?

Artifacts added by Lightroom when processing?

JPG artifacts in the exported 80 exposures?

(fyi, I don't see anything in the individual frames when I eyeball them.)

Artifacts added by Pixelmator when stacking them all with the blending mode set to lighter?

It takes a fair amount of time to make these -- and so it would be great if I could figure out how to prevent that grid from showing up next time.

Thanks in advance for any thoughts...

 

[Tommygun45]

I am not sure what grid you are talking about. Can you show us an individual frame so we can compare what either is there or isn't there. If you are talking about the white dots they are probably just lights from airplanes. Not sure how you took this or why you want to stack that many shots. Why not just take one long exposure using bulb mode if you want star trails, or use the App. I am pretty sure there is a star trails app.

 

[turnstyle]

I am not sure what grid you are talking about. Can you show us an individual frame so we can compare what either is there or isn't there. If you are talking about the white dots they are probably just lights from airplanes. Not sure how you took this or why you want to stack that many shots. Why not just take one long exposure using bulb mode if you want star trails, or use the App. I am pretty sure there is a star trails app.

Perhaps you might need to turn up your brightness a bit? It should be very obvious in the second image I posted (a crop from the first).

A regular pattern of blobs across the image.

 

[Michael Fritzen]

Hi,

if you're reffering to a grid pattern from brighter to darker blue, it appears also in No 1 (in 1:1 view) but the pattern size seems smaller. No idea though what might be the reason. If shot in RAW I'd try to check if there are regular numeric variations noticeable already in the RAW editor.

--
Cheers,
Michael Fritzen

 

[turnstyle]

Hi,

if you're reffering to a grid pattern from brighter to darker blue, it appears also in No 1 (in 1:1 view) but the pattern size seems smaller. No idea though what might be the reason. If shot in RAW I'd try to check if there are regular numeric variations noticeable already in the RAW editor.

 

[Fredy Ross]

From my single experience one has to get away from the city lights to get great shots from stacking. Here in Israel everyone goes to the desert as it isn't very far.

 

[Michael Fritzen]

Ah, ok, I didn't notice the crop factor. So it seems to be the same pattern size which for me is most visible in the top image already on the right side, right above horizon level.

 

[Bobo Hodls]

I'd wager it's the processing of the individual exposures at play. I'd try it again (if I ever tried stacking, that is [g]), set all exposure settings in camera to manual to avoid having to tweak any individual shots before feeding them to be stacked.

Then again, I've never stacked, so it's just a guess.

 

[turnstyle]

I'd wager it's the processing of the individual exposures at play. I'd try it again (if I ever tried stacking, that is [g]), set all exposure settings in camera to manual to avoid having to tweak any individual shots before feeding them to be stacked.

Then again, I've never stacked, so it's just a guess.

fyi, I shot them all RAW, with the same exposure.

In Lightroom, I gave them all the same white balance, and applied the same broad corrections to all of them at the same time (contrast, some blends, etc.)

The individual frames don't show any artifacts I can see, but there might be "enough of something" in them that, cumulatively, you can see it after stacking -- OR, perhaps it's something about the blending itself that winds up adding artifacts.

 

[blue_skies]

Hi all, I'm starting to dabble with stacking long exposures, here's something I made last night:

To make this, I:

1) Took 80 30 second exposures, with "long exposure noise reduction" off (if left on, the star trails become dotted)

2) Imported them into Lightroom, and applied the same adjustments to all of them: gave them all exactly the same white balance, some gradients, sharpening, etc..

3) Exported from Lightroom as full-size JPGs

4) Imported those into Pixelmator, stacked them as layers, and set the blending mode to "lighter", and saved a full-size JPG.

Thanks in advance for any thoughts...

Most likely it is related to the JPG adjustments you made, especially anti-aliasing (sharpening) and sublevel color encoding (JPG quality) selection.

But it seems to be affecting only planes (and satellites?), not stars. Perhaps it could just be from plane warning lights, but the dot would be visible in some of the subframes.

Can you apply the JPG adjustments post blending rather than pre?

--
Cheers,
Henry

 

[turnstyle]

Most likely it is related to the JPG adjustments you made, especially anti-aliasing (sharpening) and sublevel color encoding (JPG quality) selection.

But it seems to be affecting only planes (and satellites?), not stars. Perhaps it could just be from plane warning lights, but the dot would be visible in some of the subframes.

Can you apply the JPG adjustments post blending rather than pre?

Just to be sure we're talking about the same thing -- do you see a regular geometric grid across the whole sky, almost like a blurry honeycomb? (Or are you talking about the actual streaks of light?)

My concern is the geometric grid.

I have to try try re-exporting from Lightroom as something other than JPG (the first set were JPGs at 100%), and blending those -- unfortunately I don't have the layering very well-automated yet.

 

[zackiedawg]

The individual frames don't show any artifacts I can see, but there might be "enough of something" in them that, cumulatively, you can see it after stacking -- OR, perhaps it's something about the blending itself that winds up adding artifacts.

This is my thinking - if you see nothing of the sort in any individual shot, but it shows up in the stacking, it might just be something so faint and distant that would never be noticed that then only shows up from all the stacks together, especially if stacking to lighten. Have you tried other stacking modes - maybe without lightening - or only lighten half the stacks and not the rest? Have you tried cranking up one individual frame to ridiculous levels and see if you can see the faint grid pattern? If yes, then it might be somewhere deep inside the shot a minor effect of a sensor reflection that doesn't show up in the regular shot, but if it's there in the distant background, super-faint, and then the stacking 80 times just enhances it over and over so much that it starts to come out.

 

[blue_skies]

Most likely it is related to the JPG adjustments you made, especially anti-aliasing (sharpening) and sublevel color encoding (JPG quality) selection.

But it seems to be affecting only planes (and satellites?), not stars. Perhaps it could just be from plane warning lights, but the dot would be visible in some of the subframes.

Can you apply the JPG adjustments post blending rather than pre?

Just to be sure we're talking about the same thing -- do you see a regular geometric grid across the whole sky, almost like a blurry honeycomb? (Or are you talking about the actual streaks of light?)

My concern is the geometric grid.

I have to try try re-exporting from Lightroom as something other than JPG (the first set were JPGs at 100%), and blending those -- unfortunately I don't have the layering very well-automated yet.

My comments were towards the dots in the pattern. Some have streaks, others have not.

But yes, I can see the 'honeycomb' faint geometric grid in the image. This appears very much to be structure of the PDAF cells in the sensor.

I am guessing that the JPG optimization and the JPG stacking method, combined with the long exposure time, are the root causes of this.

This is also why I think that the A7r (no-compromise IQ) and the A7s (low light optimized) do not have the PDAF cells.

I am pretty sure that you can make this grid 'disappear', but it may take some trial and error until you find an acceptable workflow. E.g., you could perhaps just 'filter out' the grid.

 

[biza43]

Try stacking them using StarStax, it's free and a great programme.

To me, the grid seems almost like pixel borders.

 

[Lightshow]

It's an interesting problem for sure, I have a feeling it's from the processing prior to combining the 80 frames, it appears to be some sort of digital artifact, it may be multiplied due to the high frame count, try combining the shots without processing(or at the least minimal processing).

Since you are not using the Long Exposure NR in camera, are you doing any sort of black frame noise reduction in post?

As a last resort, take a 30 second exposure black frame(both with and without LongExposureNR), apply similar processing, make 80 copies, combine them, then use PS to cancel out the remaining artifacts.

--
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My lenses:
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You can't depend on your eyes when your imagination is out of focus.
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####Where's my FF NEX-7 ?????

 

[turnstyle]

Anybody here happen to be familiar with Automator and Pixelmator?

The catch for me is that it's still a cumbersome process -- I'd love to figure out a way to automatically process a folder of photos through Pixelmator -- and I'm assuming Automator can be used for something like that.

But I'm fairly new to Mac, and have no clue how to go about it.

 

[Fat Dave]

Looks like aircraft strobes to me.

 

[turnstyle]

Looks like aircraft strobes to me.

It's not the streaks of lights or dotted lines -- there's a dim (but still easily noticeable) grid pattern across much of the image -- you might need to turn up your brightness a bit -- but it's distracting and weird.

The dotted lines are planes flashing a light -- what I'm looking into debugging is the dim repeating pattern across the image.

 

[mike105105]

I would try saving the images as something other than jpeg just to eliminate compression artifacts as the cause. What other file types does the stacking program accept?

Mike

 

[turnstyle]

Yes, I want to try -- but first I want to see if I can figure out how to get Automator to work -- because right now it's a labor-intensive process.

I can export TIFF or PNG or whatever from Lightroom, and use that as the transport.

But I'm hoping to figure out how to automate, as these are big sets of files.