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Old 01-01-2014, 05:10 PM
malau (David)
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noise when photoshop?

Hi All,

took an image of orion nebular and seems when I do curves the noise come out. Are there anyone can tell me what should I do to remove or reduce it?

Many thanks.

p.s. I did DSS, dark, bias frame..etchttp://img716.imageshack.us/img716/7506/rloj.jpg
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Old 01-01-2014, 05:28 PM
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The best way is to collect more data - either longer subs or more of them or both. This way when you stack the image you'll improve the signal to noise ratio.

You can get PS plugins that try to reduce noise however it is better if the stacked image is low noise to begin with. I have the noise ninja PS plugin but there are others like topaz and neat image.

Here is your image with a quick noise ninja treatment.
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Old 01-01-2014, 05:29 PM
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is that a single frame? the only real way to combat noise (without lowering the ISO, assuming you have a dslr) is to stack more images. Stacking increases the signal (the object in the image) to noise ratio. the more frames the noise reduces but the signal becomes more obvious and more detail will be seen.

You could use some noise reduction software, but you will lose detail in the Nebula.
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Old 01-01-2014, 11:21 PM
malau (David)
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Quote:
Originally Posted by peter_4059 View Post
The best way is to collect more data - either longer subs or more of them or both. This way when you stack the image you'll improve the signal to noise ratio.

You can get PS plugins that try to reduce noise however it is better if the stacked image is low noise to begin with. I have the noise ninja PS plugin but there are others like topaz and neat image.

Here is your image with a quick noise ninja treatment.
Thanks. Yours is much nicer than mine
When you talking about sub, do you mean "light" in dss?

Before I DSS, I use bridge camera raw to reduce the noise from raw file. Should I do this way? many thanks.
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Old 02-01-2014, 09:20 PM
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Subs is short for sub exposures - most astro photos are a combination of multiple individual exposures. As an example I typically take 5 minute sub exposures but might do 12 or more of them for each colour filter and then combine them in a stacking program like Deep Sky Stacker (I actually use Pixinsight). I've attached an example of a single 5 min sub (image 1) and a stacked set of 9x5 min subs (image 2) from the same night/target so you can see the difference in the signal to noise ratio - the stack of multiple subs has a lot less noise. Both frames are post calibration so have been corrected for flats and darks.
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Old 02-01-2014, 09:59 PM
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Quote:
Originally Posted by malau View Post
Hi All,

took an image of orion nebular and seems when I do curves the noise come out. Are there anyone can tell me what should I do to remove or reduce it?

Many thanks.

p.s. I did DSS, dark, bias frame..etc

In Photoshop you use an inverted layer mask to get rid of noise in low signal areas..

see Louie's video here:

http://www.youtube.com/watch?v=32Mj2Ia-tC0


A whole series is here & they are all essential to process photos:

http://www.youtube.com/channel/UCJ5b6pFHBGe66vsuSaXb-0A


cheers
Allan
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Old 02-01-2014, 10:23 PM
malau (David)
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Thanks everyone. Learn from you guys everyday.

I guess my problem is I dont have (budget tight) different filter. I only have 1 for my camera atm......

Should I do sth like lower iso but more pic to stack? I have orion motor drive so although I can expose longer I found that once longer than 2 mins the star trails may come out. or I didnt polar align properly?
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Old 03-01-2014, 11:01 PM
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Also dithering your images will enable detail gain with removal of hot and cold pixels from your subs which overall will help with noise removal, but as others have clearly stated you need more subs to combine.
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Old 04-01-2014, 12:17 AM
malau (David)
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Thanks everyone. Since I have the basic equipment (finally get the motor drive)... what I may do is take many photos as you guys suggested with 2 mins max (otherwise seems the star trail will be appear) and try again.
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