Pages: [1]   Go Down

Author Topic: Long Exposure hot pixels?  (Read 2086 times)

dwdallam

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2044
    • http://www.dwdallam.com
Long Exposure hot pixels?
« on: October 29, 2012, 03:22:13 AM »

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, 03:29:30 AM by dwdallam »
Logged

BartvanderWolf

  • Sr. Member
  • ****
  • Online Online
  • Posts: 5778
Re: Long Exposure hot pixels?
« Reply #1 on: October 29, 2012, 05:08:13 AM »

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
Logged
== If you do what you did, you'll get what you got. ==

dwdallam

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 2044
    • http://www.dwdallam.com
Re: Long Exposure hot pixels?
« Reply #2 on: October 29, 2012, 05:24:17 AM »

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.
Logged

BartvanderWolf

  • Sr. Member
  • ****
  • Online Online
  • Posts: 5778
Re: Long Exposure hot pixels?
« Reply #3 on: October 29, 2012, 06:06:39 AM »

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
Logged
== If you do what you did, you'll get what you got. ==

Doug Peterson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 3429
    • http://www.doug-peterson.com
Re: Long Exposure hot pixels?
« Reply #4 on: October 29, 2012, 09:43:26 AM »

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.
Pages: [1]   Go Up