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Archive 2014 · Specks on Photo

  
 
TSLA
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p.1 #1 · p.1 #1 · Specks on Photo


Went out for my third try at long exposure photography this afternoon. When I was processing the photos from this session in LR5, I noticed different colored specks on it. Some specks were white, some were purple and others were red. I posted a sample photo below. Please excuse the huge size of the photo; I just thought I'd post the biggest size possible so that you could see the specks more easily. Do you know what these specks are?

Manhattan Beach Pier by TSSB, on Flickr



Apr 13, 2014 at 11:15 PM
Ben Horne
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p.1 #2 · p.1 #2 · Specks on Photo


Those are pixels that fail during long exposures. It's a completely normal characteristic of digital cameras when using long exposures. Many cameras will have a long exposure noise reduction mode that can get rid of them in camera, but that often involves a process where the camera does an exposure of equal length after the first exposure, but this time with the shutter closed. Any pixels that appear in this dark frame can then be assumed to be troublemakers in the first exposure, and then mapped out of the first exposure. Many RAW converters can also take care of these hot pixels automatically -- yet another advantage to shooting RAW.


Apr 13, 2014 at 11:30 PM
TSLA
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p.1 #3 · p.1 #3 · Specks on Photo


Ben Horne wrote:
Those are pixels that fail during long exposures. It's a completely normal characteristic of digital cameras when using long exposures. Many cameras will have a long exposure noise reduction mode that can get rid of them in camera, but that often involves a process where the camera does an exposure of equal length after the first exposure, but this time with the shutter closed. Any pixels that appear in this dark frame can then be assumed to be troublemakers in the first exposure, and then mapped out of the first exposure. Many RAW converters can also take care of
...Show more

Thanks, Ben. Does LR5 have a feature that will take care of these hot pixels automatically?



Apr 13, 2014 at 11:52 PM
gdanmitchell
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p.1 #4 · p.1 #4 · Specks on Photo


I'm wondering if something changed in the more recent versions of ACR and Lightroom. "Back in the day" ACR (and, I assume, Lightroom) automatically mapped out the hot or deal pixels. Yet, recently I have also seen them showing up in my raw images again. (I looked through ACR menus to try to find an option to turn pixel mapping on/off, but could not find one.)

By the way, this issue is not entirely limited to long exposures, though I certainly do see them in some recent night photography.

There is supposedly a method to get your Canon camera to map them out: Turn the camera on. Turn on manual sensor cleaning, but do not remove the lens. Leave it in this mode for 30 seconds. Then shut the camera off. I have no idea if this actually works, but I see it described in various places on the web.

In the meantime, you can easily delete them by using the clone tool. I use the ACR clone tool to eliminate mine.

Dan



Apr 14, 2014 at 12:31 AM
hugowolf
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p.1 #5 · p.1 #5 · Specks on Photo


It could be that Canon's DPP will be able to correct it. As far as I can remember the camera does store information about hot and dead pixels. DPP is free, a version of it would have shipped with the camera, but it would be better to download the most recent version.

ACR/Lightroom does automatically try to do this correction, it just doesn't very well.

You can also take a dark frame shot (lens cap on in a dark room or in a bag), same ISO, same shutter duration, and preferably around the same ambient temperature. You then in Photoshop add the dark frame to the image as a layer (copy and paste will add it as a new layer), then change the blending mode to subtraction - you can vary the opacity is necessary.

The camera has a few noise reduction methods: ISO noise reduction, Multi shot noise reduction, and Long Exposure noise reduction.

Brian A



Apr 14, 2014 at 10:58 AM





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