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Old 30-03-2015, 05:07 PM
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Joshua Bunn (Joshua)
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Streaking in stacked image

Hi All,

The bellow crop is from the coal sack. Its an averaged stack of 34 x 27sec exposures at 80 odd mm FL, Polar alignment was rough. A dark frame of the same exposure was subtracted from each image before averaging. The camera was a 6d at 3200 iso. Like i said, the streaking is not in each individual exposure, so i think its a problem with how im stacking or aligning the layers.

I did it in PS6, auto aligned layers, then adjusted the opacity of each layer accordingly, then flattened the image. Is there a better way to do this?

thanks
Josh
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Old 30-03-2015, 05:58 PM
LewisM
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That looks more like a bayer matrix interpolation "tartan".

I find that if I use OSC/DSLR, I need to debayer each frame individually firt BEFORE stacking and prior to aligning. If not, I get SEVERE "Tartan" images where the bayer compounds each layer.

I found it unusable in DSS (where you don't have specific options per se), but manageable, yet time consuming in CCDStack.
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Old 30-03-2015, 06:36 PM
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do you think it could be fixed pattern noise (eg from darks or flats) being smeared out by guiding drift? If your polar alignment was rough, drift could do this if you are using the same noisy dark frame throughout. looks a bit like the FPN in the image attached to -
http://www.iceinspace.com.au/forum/s...44#post1091044

If it is FPN, solution is to dither while gathering images - if it is getting in through the dark, could possibly help to get more dark data...

Last edited by Shiraz; 30-03-2015 at 07:05 PM.
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Old 30-03-2015, 08:36 PM
Alchemy (Clive)
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Try debayering your images using the proprietary software that came with the camera convert them to a 16 bit TIFF then stack, that way DSS doesn't have to do any debayer work, as per last comment more darks should improve things, if your still getting noisy images just try stacking with median combine.
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Old 30-03-2015, 10:41 PM
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I get that too at times. I find it happens when the evening humidity and temperature are high.
It's a right nuisance. No amount of darks (taken at the same temp) helped. Someone suggested dithering, that didn't help either.
In the end I caved and bought a cooled DSLR and only use my stock DSLR for long exposure work when the ambient temp is below 10C.
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Old 31-03-2015, 12:39 AM
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Quote:
Originally Posted by LewisM View Post
but manageable, yet time consuming in CCDStack.
I use ccdstack for my stl11000, so I guess i should try it, thanks Lewis.

Quote:
Originally Posted by Shiraz View Post
do you think it could be fixed pattern noise (eg from darks or flats) being smeared out by guiding drift?
Dont know Ray, I might do some research on that.

Quote:
Originally Posted by Shiraz View Post
If it is FPN, solution is to dither while gathering images - if it is getting in through the dark, could possibly help to get more dark data...
I guess these images were "dithered" between frames as there was a little polar alignment drift.

Quote:
Originally Posted by Alchemy View Post
Try debayering your images using the proprietary software that came with the camera convert them to a 16 bit TIFF then stack, that way DSS doesn't have to do any debayer work, as per last comment more darks should improve things, if your still getting noisy images just try stacking with median combine.
Thankyou Alchemy. Ill look into that.

Quote:
Originally Posted by jjjnettie View Post
I get that too at times. I find it happens when the evening humidity and temperature are high.
It's a right nuisance. No amount of darks (taken at the same temp) helped. Someone suggested dithering, that didn't help either.
In the end I caved and bought a cooled DSLR and only use my stock DSLR for long exposure work when the ambient temp is below 10C.
Thanks for sharing your experience
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Old 31-03-2015, 12:41 AM
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Quote:
Originally Posted by Shiraz View Post
do you think it could be fixed pattern noise (eg from darks or flats) being smeared out by guiding drift? If your polar alignment was rough, drift could do this if you are using the same noisy dark frame throughout. looks a bit like the FPN in the image attached to -
http://www.iceinspace.com.au/forum/s...44#post1091044
Thankyou for the link Ray, I'll have a good read through that.
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Old 31-03-2015, 09:44 AM
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I agree that it is fixed noise that has not been removed by darks that then streaks when stacked. The images will have moved due to tracking errors and when aligned the fixed noise appears as streaks.
Taking many darks and averaging them before subtracting the darks will help.
There will be random noise in a single dark and this noise is subtracted from the data image as well as the actual dark image.
Try it by taking 2 separate darks and subtract one from the other. The resulting image should be a perfectly even black image with every pixel measuring 0.
This will not be the case.
good luck with it.
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Old 31-03-2015, 12:42 PM
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Quote:
Originally Posted by Terry B View Post
I agree that it is fixed noise that has not been removed by darks that then streaks when stacked. The images will have moved due to tracking errors and when aligned the fixed noise appears as streaks.
Taking many darks and averaging them before subtracting the darks will help.
There will be random noise in a single dark and this noise is subtracted from the data image as well as the actual dark image.
Try it by taking 2 separate darks and subtract one from the other. The resulting image should be a perfectly even black image with every pixel measuring 0.
Thanks Terry!
How is the random noise subtracted from the dark image if i dont apply the dark to the dark image? Just trying to understand what you mean.
So i did the stack again, without subtracting a dark, the resulting image is bellow. Just seeing what happens.
The way im subtracting the dark is to past the dark layer on the data layer in layers then select the "difference" mode and then flatten the image. Is this the best way in PS6??

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This will not be the case.
I tried, it was not the case.
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