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06/11/2005 10:01:53 AM · #1 |
Does anyone know if canon has software to do anything about hot pixels? I can easily correct them in photoshop but its annoying. I'm using a 10D and have 12-15 hot pixels on long exposures, 30+ seconds.
Thanks
Dave |
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06/11/2005 10:15:20 AM · #2 |
The 10D does not have in-camera dark-frame subtraction, whichis what's needed to get rid of the hot pixels. To minimize the appearance of hot pixels, limit the ISO setting. Unless absolutely necessary, I never use ISO settings greater than 200 for long exposures.
No matter technique, some will inevitably still show up on very long exposure, and so it's still necessary to get rid of them after the fact. In order to do this, follow these steps:
- Take your long exposure
- Immediately take another exposure with the same settings, but with the lens cap on. You may also want to cover the viewfinder to keep stray light out of there. Canon provided a cover that's integrated into the original equipment strap, if you have that on the camera.
- In photoshop, load the long exposure, then copy the "dark frame" as a layer over the top of it. Set the blending mode to "difference". The hot pixels (and any other fixed-pattern noise) will be minimized.
Note that the subtraction should be performed on the as-shot files, with no exposure or WB compensation applied. The compensations will affect the dark frame and the photo dfferently, and mess up the subtraction.
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06/11/2005 10:28:34 AM · #3 |
Originally posted by kirbic:
The 10D does not have in-camera dark-frame subtraction, whichis what's needed to get rid of the hot pixels. To minimize the appearance of hot pixels, limit the ISO setting. Unless absolutely necessary, I never use ISO settings greater than 200 for long exposures.
No matter technique, some will inevitably still show up on very long exposure, and so it's still necessary to get rid of them after the fact. In order to do this, follow these steps:
- Take your long exposure
- Immediately take another exposure with the same settings, but with the lens cap on. You may also want to cover the viewfinder to keep stray light out of there. Canon provided a cover that's integrated into the original equipment strap, if you have that on the camera.
- In photoshop, load the long exposure, then copy the "dark frame" as a layer over the top of it. Set the blending mode to "difference". The hot pixels (and any other fixed-pattern noise) will be minimized.
Note that the subtraction should be performed on the as-shot files, with no exposure or WB compensation applied. The compensations will affect the dark frame and the photo dfferently, and mess up the subtraction. |
This would obviously be illegal for challenge purposes, yes?
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06/11/2005 10:31:45 AM · #4 |
Originally posted by rgo:
This would obviously be illegal for challenge purposes, yes? |
Good point. Unfortunately, the answer is "yes", for both Basic and Advanced challenges :-(
Thre reason, of course, is that it uses more than one source image. It is legal, however, if the camera itself performs the dark frame subtraction. Most newer DSLRs are able to do this, but the 10D is not capable of it.
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06/11/2005 10:43:31 AM · #5 |
Originally posted by kirbic:
Originally posted by rgo:
This would obviously be illegal for challenge purposes, yes? |
Good point. Unfortunately, the answer is "yes", for both Basic and Advanced challenges :-(
Thre reason, of course, is that it uses more than one source image. It is legal, however, if the camera itself performs the dark frame subtraction. Most newer DSLRs are able to do this, but the 10D is not capable of it. |
Is there a way to tell if this process has been performed on an image? Submitting the original shot with exif intact would "validate", or no?
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06/11/2005 11:18:26 AM · #6 |
If the camera performs the dark frame subtraction, there's no way to tell later whether it was done, and for validation poutposes we don't care, since it's always legal if done in-camera.
For dark frame subtraction done later, yes, we can tell if it has been done.
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