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10-07-2014, 09:35 PM   #1
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Checkerboard Pattern in Star Trails



I'm having a weird issue with a star trails image and I've never had it before. When I merge the layers I get this checkerboard pattern. It's actually visible before the merge but is very faint.

To build the star trails I'm stacking the images in Photoshop as layers and the using "lighter color" as the blending mode for every image except the bottom, which remains on normal. There are 96 images in the stack.

As an experiment, I tried it with only half the images and the checkerboard pattern still occurs. Does anyone have any idea what's causing this? I've stacked upwards of 200 images in a star trails in this manner before and never had an issue like this.

10-10-2014, 09:12 AM   #2
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When weird stuff happens I will go back an retrace to see if there is hardware or software that changed between when it worked properly and when it broke.
I don't have a specific source for you but that is all I can suggest.
Did you do an upgrade in anything?
Did you use a different camera or setting?
10-10-2014, 11:51 AM   #3
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I've had this before which had something to do with my blend layers not being at 100% opacity. Try merging all visible layers (do a save-as first so as not to lose your layers in case this doesnt work) and then duplicate the resulting layer. If the layer wasn't at 100% opacity for some reason, stacking a duplicate over it should remove the matrix. good luck.
10-10-2014, 02:18 PM   #4
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QuoteOriginally posted by crewl1 Quote
Did you do an upgrade in anything?
Did you use a different camera or setting?
So no upgrades and no setting changes. Interestingly, in the eight or so ST shots I compiled that weekend with this camera, this is the only one that had this issue. And I used the same lens for other shots, too. What's weird is that the pattern worsens with the number of layers, but it's present even with just two overlapping layers.

QuoteOriginally posted by mikeSF Quote
I've had this before which had something to do with my blend layers not being at 100% opacity
I'll check and see if I inadvertently nudged the blending percentage. I can say that duplicating the flattened image intensifies the pattern, except on some blending modes like Overlay where I completely lose the pattern because I lose most of the image data. I'm just not sure why it's only happening with this image and why it's over the entire image. (Especially since this is my favorite of all the shots I took this weekend.)

Thank you both for your insight. I'll play around with it some more this weekend and see if anything improves.

10-12-2014, 06:46 AM - 3 Likes   #5
mee
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Ah yes. You captured the giant Space Waffle in photograph.. Nebulons from Kleptar IV are awaiting anxiously for the Milky Way to churn enough to form Space Butter before they 'destroy' this Space Waffle near the toasty Sun.
10-12-2014, 10:09 AM   #6
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It looks to me like you have a classic case of aliasing. The stars are smaller than a pixel in each exposure, so only a single pixel is maximally exposed per star. When you combine the 'single pixels' into a composite star trail, you get a string of single pixels. Since your trails are fairly close to 45-degrees, you get a line of single pixels connecting along the diagonal. This results in the checkerboard pattern.

Have you tried the Interval Composite function on the K-3 to take your star trails? If it works well, it would save you the Herculean effort of combining all the images in Photoshop.

Cheers,
Lou
10-12-2014, 02:01 PM   #7
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No, regrettably, I didn't. I'm going to give that a shot on the next go-round in 10 days, I hope. I'm hoping to get away from work to photograph the Orionids and have star-and-meteors shot. With luck, I'll have the ocean-front beach I'm eyeing to myself.

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