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Author Topic: Long Exposure hot pixels?  (Read 1401 times)
dwdallam
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« on: October 29, 2012, 02:22:13 AM »
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I noticed today that when viewed at 100% my long exposure images have little white pixels scattered throughout the image. Not a lot, but definitely there. Exposures over 20 seconds revealed this, and the longer the more there were.

This was not a night time long exposure, but a daytime. Long exposure noise reduction was set to automatic. I don't think it ever went off though because that would have incurred another full shutter time. I didn't notice that happening, as the images would pop up s few seconds after I released the shutter.

Something wrong with my rig (1DS MKIII)?

« Last Edit: October 29, 2012, 02:29:30 AM by dwdallam » Logged

BartvanderWolf
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« Reply #1 on: October 29, 2012, 04:08:13 AM »
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Long exposure noise reduction was set to automatic.

Hi,

Have you tried setting it to 3:On, instead of 2:Auto? Automatic makes its own choices whether to use darkframe subtraction or not, and not only shuttertimes >1 sec. seem to drive that decision.

Cheers,
Bart
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dwdallam
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« Reply #2 on: October 29, 2012, 04:24:17 AM »
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Bart do you think that's a phenomenon that will get rid of what I'm seeing? If they are just noise specs, I can live with that since there aren't too many. The reason I have it set to auto is that unless I'm shooting really long exposures at night--which get noisy--I'd rather trade the time for a few hot pixels that I can fix pretty fast.
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BartvanderWolf
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« Reply #3 on: October 29, 2012, 05:06:39 AM »
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Bart do you think that's a phenomenon that will get rid of what I'm seeing? If they are just noise specs, I can live with that since there aren't too many. The reason I have it set to auto is that unless I'm shooting really long exposures at night--which get noisy--I'd rather trade the time for a few hot pixels that I can fix pretty fast.

Hi,

If the bright/hot pixels are caused (which is likely at 20 seconds) by the long exposure, then a darkframe subtraction should be able to reduce or eliminate them. In principle all systematic sensor non-uniformity can be removed with a darkframe. If time on location is an issue, you could try shooting separate darkframes (body cap on, same exposure time and ambient temperature, viewfinder closed) at a different moment, and then use a Raw converter like RawTherapee which allows to do darkframe subtraction as an additional processing step.

It is also possible that you have a sensor calibration issue, but that would also show on normal exposures, so based on your description that doesn't seem to be the issue here.

Cheers,
Bart
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Doug Peterson
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« Reply #4 on: October 29, 2012, 08:43:26 AM »
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PLEASE try these images in Capture One 7 and turn up the "single pixel" noise reduction slider.

I think you'll be floored just how much better this file is handled in Capture One 7 than in ACR/LR.

Or send me an email with a link to the raw file and I'll do the work/comparison for you.
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