Long exposure noise reduction.


- Zeto -

New Member
Jun 12, 2010
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#1
Hi guys,


I'm new and have some questions about this.


I'm using a Canon 7D. It has this function called "Long exposure noise reduction"

The problem i am facing now is that, if i turn this on, and if i do a long exposure......

For eg, 60 seconds..., then the shutter will open and close for 60 seconds, then take another 60 seconds to load the picture. It takes twice the time for a picture to load. Does this happens to u guys as well?
And also... If u turn it off, the picture will appear in 60 seconds straight after shutter closes.

However, i realise, for pictures over a few seconds, if i don't turn this on, then i start to have white/blue/red dots that are bigger, then small small white dots everywhere(refer to pic). Is this due to the reduction that is turned off? Or are they hot pixels, or are they dust?

Is there any way i can go about solving this? Below is a picture of it without turning on this "Long exposure noise reduction" function.

 

Last edited:

daredevil123

Moderator
Staff member
Oct 25, 2005
21,662
69
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lil red dot
#2
Hi guys,


I'm new and have some questions about this.


I'm using a Canon 7D. It has this function called "Long exposure noise reduction"

The problem i am facing now is that, if i turn this on, and if i do a long exposure......

For eg, 60 seconds..., then the shutter will open and close for 60 seconds, then take another 60 seconds to load the picture. It takes twice the time for a picture to load. Does this happens to u guys as well?
And also... If u turn it off, the picture will appear in 60 seconds straight after shutter closes.

However, i realise, for pictures over a few seconds, if i don't turn this on, then i start to have white/blue/red dots that are bigger, then small small white dots everywhere(refer to pic). Is this due to the reduction that is turned off? Or are they hot pixels, or are they dust?

Is there any way i can go about solving this? Below is a picture of it without turning on this "Long exposure noise reduction" function.
I always turn off Long Exp NR. I will do my NR in PP.
 

wildcat

Senior Member
Sep 8, 2004
3,269
1
38
Bedok
#4
Noise is noise. However I don't know why there are so many solid white dots. Could be hot pixels... they look a bit too solid to be noise.

Suggestion: try to take another pic, or different orientation.
If they are hot/dead pixels, the spots should appear at the same exact spots. You may have other pictures to compare with.

I have one red dot on my camera that normally appears during LE, and it's always on the same spot. I don't use LE noise reduction though.
 

- Zeto -

New Member
Jun 12, 2010
65
0
0
#8
There is a few constant red/blue/white dots so far i noticed at the same place.

However, it only appears if u expose over 60 seconds.

If not, it doesnt appear.

Is this the sensor problem, or the lens problem? or the filter problem? I have a ND filter
 

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Octarine

Moderator
Staff member
Jan 3, 2008
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Pasir Ris
#9
There is a few constant red/blue/white dots so far i noticed at the same place.
However, it only appears if u expose over 60 seconds.
If not, it doesnt appear.
Is this the sensor problem, or the lens problem? or the filter problem? I have a ND filter
Lens: elements are moving and the sharp image only appears at the sensor. Everything in front is blur. Unlikely that this will cast such a sharp dot-like image on the sensor.
Filter: Further away from the sensor than any lens element. Even a finger print will not show up in your images. You could simply remove it to test.
Google / Search here for 'hot pixels'.
 

ZerocoolAstra

Senior Member
Mar 13, 2008
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rainy Singapore
#10
If I remember correctly, Long Exp noise reduction causes the camera to take another exposure which is of equivalent duration as the original exposure.
The 2nd exposure is completely dark, and reveals the location of the hot pixels, which the camera's processor will subtract from the original exposure.

Long Exp NR doesn't remove signal noise.
 

wildcat

Senior Member
Sep 8, 2004
3,269
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Bedok
#11
If I remember correctly, Long Exp noise reduction causes the camera to take another exposure which is of equivalent duration as the original exposure.
The 2nd exposure is completely dark, and reveals the location of the hot pixels, which the camera's processor will subtract from the original exposure.

Long Exp NR doesn't remove signal noise.
Hmm... interesting enough KR and DP has articles on these, and you're right! It would explain why a hot pixel can have it's noise reduced using LENR (which is different from high ISO NR).
 

daredevil123

Moderator
Staff member
Oct 25, 2005
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lil red dot
#13
TS, I think you have a problem with the sensor overheating.

When long exposure, some pixels overheat and hot spots appear. 60s shouldn't be causing this problem. Usually when photographing star trails we sometimes see this if we do 30min exposures or something. You need to bring your camera to CSC to get them to look at this. I really hope you still have warranty on the your 7D.
 

night86mare

Deregistered
Aug 25, 2006
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#14
for crying out loud, please don't post such large pictures - just the crop of the area with the hot pixels will do.
 

Numnumball

Senior Member
Mar 6, 2009
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#15
Long Exposure NR is simply redundant, i see no diff with it or without it.. If there's a need to reduce noise, there's likes of noise ninja amid some others pp software..
 

jsprtan

New Member
May 12, 2010
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CEntral
#17
Hot pixel is always there even on new camera and at factory they will do a cmos mapping as part of the process. From what I read, any thing longer than 2 to 3 sec they will show up. What I think u can do is to do a cmos remapping. For canon, u can do this by first removing ur attached lens and caps up. Go to the menu and under one of the spanner icon there is sensor cleaning menu, Select manual cleaning and the mirror will lock up. Let it run for a minute or longer and after u are done turn off the camera. On completing, the camera will do a cmos remapping and it might help u remove the hot pixel.
 

mimik07

New Member
Oct 13, 2009
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#18
Hmm... interesting enough KR and DP has articles on these, and you're right! It would explain why a hot pixel can have it's noise reduced using LENR (which is different from high ISO NR).
A very informative thread indeed :thumbsup:

Have been experimenting with long exposures of late with ND110 and came across this issue as well and I'm having a hard time with the noise reduction process, especially for those exceeding 60secs in exposure. Currently using NR feature in DPP but always end up with pictures losing sharpness and details.

What do they mean by 'Manually cleaned image' at the end of the article? Cloning? :dunno:
 

wildcat

Senior Member
Sep 8, 2004
3,269
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Bedok
#19
A very informative thread indeed :thumbsup:

Have been experimenting with long exposures of late with ND110 and came across this issue as well and I'm having a hard time with the noise reduction process, especially for those exceeding 60secs in exposure. Currently using NR feature in DPP but always end up with pictures losing sharpness and details.

What do they mean by 'Manually cleaned image' at the end of the article? Cloning? :dunno:
Maybe I should start switching my LE exposures on again. Someone said my D5000 photo got a lot of noise :cry:
 

ZerocoolAstra

Senior Member
Mar 13, 2008
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#20
Maybe I should start switching my LE exposures on again. Someone said my D5000 photo got a lot of noise :cry:
seems like a lot of people still confused between high ISO noise and the sensor noise (hot pixels, etc)... :)

Your issue now is high ISO noise? try to overexpose slightly and the noise should be reduced, since it will form a smaller component of the entire signal.
 

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