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Old 03-06-2008, 06:33 AM
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DSLR in camera noise reduction?

Hi All, I note my Canon 40D has 2 settings for in-camera noise reduction...

what's the feeling out there - do you guys use the in-camera noise reduction for astro work or rely on post-processing to remove noise?

cheers,

Rob
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Old 03-06-2008, 07:17 AM
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Rob, ICNR is the way to go, it dose increase your image run, but it is worth the effort, unless you can match the temp's very closely.

Leon
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Old 03-06-2008, 07:29 AM
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Quote:
Originally Posted by leon View Post
Rob, ICNR is the way to go, it dose increase your image run, but it is worth the effort, unless you can match the temp's very closely.

Leon
Thanks Leon, pardon my ignorance on this (complete novice), but why does it increase your image run? Also, when you say "unless you can match temp's very closely" are you suggesting that ICNR be used instead of darks which I understand would need to be taken at same temp as the lights?

And one final question can ICNR deal with hot pixels?

Thanks again for your help.

cheers,

Rob
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Old 03-06-2008, 07:41 AM
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Rob

ICNR is where the Canon 40D automatically takes “Dark Frames” after each light exposure.

When this is enabled (User sets “C.Fn II–1” to “2=On”) then the 40D will take a Dark for every exposure over 1 second.

So, when you take a 3 minute exposure of say, M83, the 40D will automatically begin a 3 minute “Dark” exposure (ICNR) as soon as the M83 light is completed. This effectively doubles your imaging time, i.e. 3 min M83 + 3 min Dark = 6 mins total.

On my SBIG ST7E, where the cooling temperature is regulated, I have the luxury of taking say, 10 x 3 minute lights of M83 consecutively, followed by say, 5 x 3 minute darks at the end of the imaging run as the chip is at the same temp throughout.

I think that Bert has investigated ICNR on the 5D fairly comprehensively and IIRC, his recommendation was to use ICNR rather than switch it off and try to apply separate Darks later on.

Cheers

Dennis
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Old 03-06-2008, 09:10 AM
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Thanks Dennis - great info. At the moment (and assuming I will ever be able to image again with this damn weather) I am using Images plus to control the camera and setting it up to take a range of Lights then a range of darks... do you know if I can use the ICNR with images plus just doing a run of lights or will this over-ride the ICNR?

cheers,

Rob

Quote:
Originally Posted by Dennis View Post
Rob

ICNR is where the Canon 40D automatically takes “Dark Frames” after each light exposure.

When this is enabled (User sets “C.Fn II–1” to “2=On”) then the 40D will take a Dark for every exposure over 1 second.

So, when you take a 3 minute exposure of say, M83, the 40D will automatically begin a 3 minute “Dark” exposure (ICNR) as soon as the M83 light is completed. This effectively doubles your imaging time, i.e. 3 min M83 + 3 min Dark = 6 mins total.

On my SBIG ST7E, where the cooling temperature is regulated, I have the luxury of taking say, 10 x 3 minute lights of M83 consecutively, followed by say, 5 x 3 minute darks at the end of the imaging run as the chip is at the same temp throughout.

I think that Bert has investigated ICNR on the 5D fairly comprehensively and IIRC, his recommendation was to use ICNR rather than switch it off and try to apply separate Darks later on.

Cheers

Dennis
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Old 03-06-2008, 10:41 AM
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Rob your camera controls the ICNR, so using Image Plus there is no reason to set it to take the darks at all, just set the camera to ICNR on 2, set Image Plus to take the lights at the desired length, tell Image Plus not to take darks at all, the camera will take care of it.

Just do some flats before hand, and process the lights as they are with the flats, as the darks are already taken care of.

Leon
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Old 03-06-2008, 11:04 AM
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Thanks Leon

Flats will be my next challenge
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Old 03-06-2008, 11:49 AM
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The Rho complex pic I posted recently had no ICNR and was a stack of 20 10minute subs at iso1600.

http://s231.photobucket.com/albums/e...t=RhoLarge.jpg

Turned out not too badly - I expected loads and loads of noise, but I only applied very minimal NR with the Noise Ninja plug-in which had only a subtle effect.

Noise (and the lack of it) confuses me!!!!!
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Old 03-06-2008, 12:07 PM
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Rob, to expand a bit on what others have replied with.

ICNR = great...but it only deals with REPEATABLE NOISE. It doesn't deal with random noise in the darks (each dark and light will have a certain amount of random noise. Depending on temperature (see below), this may or maynot be an issue

Taking darks after and then applying them = could be great.... but often isn't. Stacking a multiple of Darks will deal with repeatable noise as well as reducing random noise by the sq rt of the number of darks you use to create a master. This is a very desirable thing. UNFORTUNATELY..... your darks, unless taken at the same temperature will have differing amounts of dark current so combining them will not necessarily have the same dark current as your lights. In fact most probably not.

If there was say a 6 degree drop in temp between taking your lights (which will have different amounts of noise 'cos the temp is dropping anyway) and the final dark you taken, then there will be 1/2 the noise in the final dark as in the first light.


what does this all mean....IF you temp is stable (<2 or 3 degree maximum change ) then yes taking darks at the end can be a good thing, especially if you are pushed for light time. If though your temp is dropping (or rising) then consensus seems to be to take ICNR.

HTH

BTW non-random noise is not really noise by definition, it should really be described by something like unwanted signal or detrimental signal or something similar. jmo
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Old 03-06-2008, 02:14 PM
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Paul,
Wouldn't the "Random" noise only be a problem if you are taking a single long exposure.
I'd assume that stacking of multiple images would cancel the "random" noise out.
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Old 03-06-2008, 02:33 PM
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That is true for stacking the final lights Jeanette, but the ICNR is only a single dark frame applied to the each image, so the random noise of the dark is also subtracted from the light. This is where multiple darks beat the ICNR as you can reduce the random noise by stacking and creating a master dark. That option isn't available in the ICNR.
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Old 03-06-2008, 03:46 PM
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AGGGHHHHH.. my head's exploding

but thanks, I appreciate the detailed advice...and I thought planetary imaging was fraught with complexity
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Old 03-06-2008, 04:01 PM
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It's actually pretty straight forward Rob. It's just like baking a cake, you just have to get the ingredients right, in the right order, using the right cake tin (making sure the tin is greased )and baked at the right temperature.

It putting the icing on the cake afterward in photoshop that really that will reeeallly boil your noodle. (don't ask me what noodles have to do with cake baking )
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