Author Topic: Unknown gradient/backgrounf Noise how to remove  (Read 2877 times)

Offline tdgm

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Unknown gradient/backgrounf Noise how to remove
« on: 2016 September 18 10:58:31 »

Hello everyone

Have an unusual gradient or noise . I am not sure what it is and definitely unsure how to get rid of it. Just review the attached JPEG. Noticed areas on right of brighter noise than the rest of the background. Background modelization does not seem to remove it. Would multiple modelizations remove this and if not what do you guys/gals think would help.

Offline Greg Schwimer

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #1 on: 2016 September 18 11:23:12 »
I'm looking at this on my phone...I  see a semi circular pattern on the right, and possibly on the left as well. Is this what you're referring to? Looks almost like a reflection or light leak. Could it be moonlight?
- Greg
Scottsdale, Arizona, USA

Offline tdgm

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #2 on: 2016 September 18 11:49:25 »
Actually 2 areas on the right  one is inside about 5 stars blueish color


Steve

Offline Greg Schwimer

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #3 on: 2016 September 18 17:42:20 »
Yes, I see it. In fact, there may be 4 in total - one on the far left, 3 on the right. It looks like a reflection or light leak maybe but not sure. You can clean it up with a mask and curves adjustment. I gave it a quick try. Result is attached.


 - Extract a luminance copy of the image.
 - Using MMT remove layers 1-5
 - Use HT to clip the blacks heavily, adjust so the artifact is relatively bright
 - Using PixelMath with a formula of "0", create a new image as a black reference.
 - Use the black reference as a source image to paint over the stars, etc using clone stamp leaving only the artifact.
 - Apply the result as a mask.
 - Use CurvesTransformation to suppress the artifact.



- Greg
Scottsdale, Arizona, USA

Offline Herbert_W

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #4 on: 2016 September 19 01:39:37 »
Hi,

here is a tutorial how to use a black image and clonestamp to create a 'mask' - http://www.skypixels.at/downloads/videos/mask_clonestamp.mp4

The video is in german language - but it should be possible, to follow the individuell steps.

Best regards!

Herbert, Austria


Offline msmythers

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #5 on: 2016 September 19 02:00:31 »
Hubert

Thanks. I'd forgotten what the order was for using clonestamp with a second image. My german is nonexistent but I was able to understand 'OK'.


Mike

Offline tdgm

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #6 on: 2016 September 19 08:10:13 »
Thanks Schwim I am just a beginner will work on my clone stamping skills when I can and thanks for all he help. There is never a dull moment with processing astro images.


Steve

Offline Greg Schwimer

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #7 on: 2016 September 19 13:02:06 »
Thanks Schwim I am just a beginner will work on my clone stamping skills when I can and thanks for all he help. There is never a dull moment with processing astro images.


Steve
No problem!

I would look at where the artifact came from. If it's being caused by a reflection or light leak it would be best if you solve that problem with the equipment. It's far easier to not have to process it out.
- Greg
Scottsdale, Arizona, USA

Offline tdgm

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #8 on: 2016 September 19 13:29:41 »
Hello Schwin

Last night I tried process the image again starting with a different Flat Filed Master. Apparently those semicircular patterns line up with the edges of dust donuts in the flat fields. I might have to work on my flat  flied creations. Both field images were created with in Batch PreProcessing and than reused as a master.  might have to create a master with Image calibration and Image integration outside of BPP.

Offline Greg Schwimer

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #9 on: 2016 September 19 13:54:47 »
Ah, that would do it as well. Now that I think about it, I ran into something similar last night using BPP (which I rarely do). Turns out BPP expects uncalibrated master darks whereas mine was calibrated. It calibrated this already calibrated dark which caused the flats to overcorrect. The dust donuts became light rings.

This is probably easier to fix than isolating a reflection. I hope that's the case!
- Greg
Scottsdale, Arizona, USA

Offline tdgm

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #10 on: 2016 September 22 12:02:10 »
I think I have tracked it down to the actual flat field images and that the dust donuts illumination is not equal the darker circles are the ones that have remains in the final integrated image. So I might have exposed for to long. Trying to get a max ADU of 42000 for STF 8300C and maybe I need to lower that number.  Does that sound plausible?

Steve

Offline Starcruiser

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #11 on: 2016 December 28 11:07:12 »
I have a ST8300M and just started using the STF8300C but I did save this information in my notebook from the CCDStack forum, so they appear to recommend around 33,000 average for the 8300"

"Well, 65535 is the max number possible in ADU. So we won't go into a lot of technical equations, not really needed.
Yes, you want to use Maxim, CCDStack or some program that will give you the average ADU of the flat and that is the ADU level that concerns you.
Try to get 33,000 average and that should give you a nice flat. The other number you want to try to get is a total of about 500,000 ADU. so you want to use 12-25 flats per filter, depending on your time you have to do flats. Then make a master flat from these exposures.
Due to the use of a mechanical shutter, you want to keep the exposure at 3 seconds or so, so the shutter does not show in the flat."
« Last Edit: 2016 December 28 14:15:20 by Starcruiser »

Offline tdgm

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Re: Unknown gradient/backgrounf Noise how to remove
« Reply #12 on: 2016 December 29 11:02:46 »
Hello Starcruiser

Thanks for the reply. I have been taking the flats with a maximum 65 K with a mean of 40k-42K and have no problems. Creating the flats was just confusing because nobody ever spelled out using the 42k as max or mean so was trying both. Also once i got a flat man and I could adjust the light it also helped.


Thanks again


Steve