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01/08/2005 06:31:07 PM · #1 |
I've heard quite a bit about dark frame subtraction for long exposures and nightshots. How is that done. Details please.
Thanks
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01/08/2005 06:36:58 PM · #2 |
Some cameras have this built in for noise reduction. For the ones that don't there's a program called Dark Frame which I believe is free. Someone may even know how to do it in PS.
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01/08/2005 06:37:42 PM · #3 |
1.) Take your actual exposure
2.) Put lens cap on
3.) Take "dark frame" exposure
4.) edit:
In photoshop, load the image, then copy in the dark frame image as a layer on top. Set blending mode on the dark frame layer to "difference" and opacity to 50%.
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01/08/2005 06:45:21 PM · #4 |
| is there an example photo of this somewhere? Im guessing this would just change a dark background to a light one, but im interested to see how this would look. |
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01/08/2005 06:49:30 PM · #5 |
Originally posted by nico_blue:
is there an example photo of this somewhere? Im guessing this would just change a dark background to a light one, but im interested to see how this would look. |
No, this is a noise reduction technique.
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01/08/2005 06:49:56 PM · #6 |
Dark Frame subtraction removes some noise from long exposures. That's it. By subtracting a black frame taken at settings as a long exposure, you can take out some of the things that your sensor may have added.
It's more work, and may not remove all the noise, but it may be worth it especially if your sensor makes a lot of noise. Use NeatImage or an equivalent afterwards.
Message edited by author 2005-01-08 18:51:14. |
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01/08/2005 06:57:14 PM · #7 |
| oh thanks! learn something new everyday here :-) |
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01/08/2005 08:01:18 PM · #8 |
Originally posted by kirbic:
4.) edit:
In photoshop, load the image, then copy in the dark frame image as a layer on top. Set blending mode on the dark frame layer to "difference" and opacity to 50%. |
Thanks.
That was exactly what I was looking for.
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01/08/2005 08:04:04 PM · #9 |
Nah, I wont, I was gonna say that Nikon's D70 does that for you. But I wont, cuz It could start one of those Mac vs PC type wars again ;)
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01/08/2005 08:09:09 PM · #10 |
Originally posted by Arcanist:
Nah, I wont, I was gonna say that Nikon's D70 does that for you. But I wont, cuz It could start one of those Mac vs PC type wars again ;) |
Nah, we'll just upgrade to 20Ds. they will do it as well.
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01/08/2005 08:09:45 PM · #11 |
Originally posted by kirbic:
4.) edit:
In photoshop, load the image, then copy in the dark frame image as a layer on top. Set blending mode on the dark frame layer to "difference" and opacity to 50%. |
Do you really need to shoot the extra image? Wouldn't it look the same to use a layer with a black background created in PS? |
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01/08/2005 08:13:43 PM · #12 |
Originally posted by aronya1:
Originally posted by kirbic:
4.) edit:
In photoshop, load the image, then copy in the dark frame image as a layer on top. Set blending mode on the dark frame layer to "difference" and opacity to 50%. |
Do you really need to shoot the extra image? Wouldn't it look the same to use a layer with a black background created in PS? |
Nope, absolutely not. The dark-frame image is of course not completely black, it contains noise. Some of the noise, referred to as "fixed pattern noise" is the same from frame to frame. Hot pixels are an extreme example of fixed-pattern noise. When you subtract (the difference blending step) the dark frame from the image, the fixed pattern noise gets subtracted, resulting in lower noise without loss of image detail.
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01/08/2005 08:18:32 PM · #13 |
| Thanks for clearing that up. Pun intended. |
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01/08/2005 08:45:28 PM · #14 |
| Ideally, your dark frame should be made using the same exposure time and in the same environmental conditions as the actual exposure. |
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01/08/2005 09:56:20 PM · #15 |
| Same ISO and shutter, and other in camera settings the same, but aperture doesn't matter, of course, as the lens cap is on. |
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