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Thread started 30 May 2010 (Sunday) 07:07
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Is this what we call noise? (Newb alert!)

 
nüborn
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May 30, 2010 07:07 |  #1

On a 20 secs exposure at 400 ISO, I ended up with some grain but also very bright sparks randomly colored. Is this normal?

[IMAGE TOO SMALL, NOT RENDERED INLINE]

Now, I just saw that there some options turned on (to reduce the noise actually) in the setup of my Canon camera, would that happen to be the reason why I get these colored dots?

Long exposure noise reduction 1:Auto
High ISO speed noise reduction 1:On
Highlight tone priority 0:Disable

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photoPanda
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May 30, 2010 07:10 |  #2

That's not noise but hot pixels - try doing a search for that.. there are many good explanations on here :) They're more prevalent with longer exposures and can be mapped out by certain software or simply cloned out.




  
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gjl711
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May 30, 2010 07:11 |  #3

Those are hot pixels, not specifically noise. Hot pixels crop up from time to time especially on longer exposures. Sometimes they get stuck in shorter exposures as well. When they do there is a procedure that sometimes clears them. Or you can clone them out in your favorite photo editor.


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TweakMDS
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May 30, 2010 07:11 |  #4

Those are what they call hot pixels.
Long exposure noise reduction should take care of it, since it makes a second "black exposure" of the same shutterspeed and substracts all hot pixels from your original image.


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DStanic
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May 30, 2010 09:12 |  #5

Try using mirror lockup for a few minutes with the lens cap on. This actually fixed hot pixels I had on my Rebel XTi.


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nüborn
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May 30, 2010 09:38 |  #6

Thanks people, really appreciated!


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MikeFairbanks
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May 30, 2010 09:41 |  #7

THose hot pixels are easy to fix in post production. Just use your bandaid tool. Set it very small and blend 'em out.


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gjl711
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May 30, 2010 10:42 |  #8

DStanic wrote in post #10270719 (external link)
Try using mirror lockup for a few minutes with the lens cap on. This actually fixed hot pixels I had on my Rebel XTi.

It's not MLU but manual sensor cleaning mode. The procedure is as follows:
1. remove lens and replace with body cap.
2. put the camera in manual sensor cleaning mode for about a minute.
3. check to see if hot pixels have cleared by taking a pic.
4. if not, repeat the procedure again leaving it in manual cleaning mode a bit longer.

It doesn't always work but it's worked for many.


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10megapixel
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May 30, 2010 10:49 as a reply to  @ gjl711's post |  #9

Yep, those are hot pixels. Here (external link)is an example of bad noise ;)



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Old ­ Coot
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May 30, 2010 11:50 |  #10

10megapixel wrote in post #10271067 (external link)
Yep, those are hot pixels. Here (external link)is an example of bad noise ;)

Ouch :)


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tkbslc
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May 30, 2010 11:59 |  #11

Hot pixels are extremely common and you won't get rid of all them for a 20 second exposure even if Canon replaces your sensor or you try the sensor cleaning tricks. You have 3 methods for dealing with them:

1. clone them out with software. If there is just a few and you only have a couple images this might be easy. If you have a whole folder of files, probably not.
2. Use Long exposure noise reduction. This will tell the camera to take a black frame of equal exposure time as your shot and then subtract anything that is not black from the image. This works well, but the downside is each shot now takes twice as long. In this case after your 20s exposure, the camera would then take an additional 20s of processing time. Doesn't sound bad until you try an awesome 10m exposure and it takes 20m!
3. Use software designed for removing these. Rumor has it Lightroom takes care of these automatically. If you don't have lightroom, try downloading a free tool called pixel fixer. It will batch remove the hot pixels on a whole folder of RAW files at once.


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gjl711
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May 30, 2010 12:24 |  #12

tkbslc wrote in post #10271347 (external link)
...
3. Use software designed for removing these. Rumor has it Lightroom takes care of these automatically...

Lightroom and arc both remove them automagically.


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DStanic
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Jun 02, 2010 07:04 |  #13

gjl711 wrote in post #10271037 (external link)
It's not MLU but manual sensor cleaning mode. The procedure is as follows:
1. remove lens and replace with body cap.
2. put the camera in manual sensor cleaning mode for about a minute.
3. check to see if hot pixels have cleared by taking a pic.
4. if not, repeat the procedure again leaving it in manual cleaning mode a bit longer.

It doesn't always work but it's worked for many.

That is what i meant. Thanks for the clarification. :) OP give it a try!


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hpulley
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Jun 02, 2010 08:15 |  #14

Why did you take a 30s exposure at f/11 anyways? There isn't motion so unless you have an awful, awful lens you don't need f/11. There is no foreground object so it wasn't for depth of field reasons. If you'd taken a 4s exposure at f/4 it would likely have had less hot pixels showing up.


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nhbeast
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Jun 02, 2010 09:33 |  #15

10megapixel wrote in post #10271067 (external link)
Yep, those are hot pixels. Here (external link)is an example of bad noise ;)

LOL!!!


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Is this what we call noise? (Newb alert!)
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