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02/28/2004 09:51:33 PM · #1 |
I'm finding that when I take a photograph in the dark without a flash, I get these.. little miscolored pixels in my picture. What is causing this?
The one thing I considered was that maybe it was dirt on the lens? If that was the case, how would I go about cleaning the lens?
Any other thoughts on what it may be? |
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02/28/2004 10:02:15 PM · #2 |
| What you're seeing is CCD noise from the long exposure. I'm no engineer, but I believe it works like this: some pixels on your camera's sensor are more sensitive than others. On longer exposures, those pixels "overheat" and become saturated, leaving bright, colored specks on your image. |
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02/28/2004 10:07:06 PM · #3 |
| Wow. Is there any way to take care of it, besides setting a shorter exposure time? (Which I wouldn't know how to do anyway.) |
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02/28/2004 10:27:55 PM · #4 |
Those are called hot-pixels. It is just CCD noise and it happens in most to all digital cameras, just a part of digital photography. Unless it's something WAY extreme, it's not that big of a problem.I just generally re-shoot if that happens (and it does).
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02/29/2004 12:40:45 AM · #5 |
Originally posted by lindsay:
Wow. Is there any way to take care of it, besides setting a shorter exposure time? (Which I wouldn't know how to do anyway.) |
You have at least one option, possibly two. I don't know about your specific camera, but on my Nikon 995, you could set noise reduction to "on" and it would subtract a "black frame" from each shot. Look for it in the menu; you probably will need to be in manual mode to do this.
What this does is to take an exposure of equal length right after your shot, but with the shutter closed. It then subtracts the two, since the "black frame" ideally is completely black, anything that shows up in it can be subtracted. By doing this you get rid of "fixed pattern noise".
Your second option is to do this manually. I won't go into all the gory details here, suffice to say that there have been several previous forum discussions about this, and you will come up with a bunch of info if you google "black frame subtraction" or "dark frame subtraction". You should not need any special software, it can be done in nearly any image editor that supports layering.
Once you've got rid of the fixed pattern noise, you may want to experiment with stacking of multiple exposures to reduce random noise. Although it's only good for still subjects, this technique can yield amazing improvements in night shots with nearly any camera.
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02/29/2004 01:28:43 AM · #6 |
Originally posted by lindsay:
you may want to experiment with stacking of multiple exposures to reduce random noise. camera. |
Stacking ? does this mean placing each exposure on a seperate layer and flattening ?
I assume this wouldn't be allowed in the challenges ?
Paul. |
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02/29/2004 01:31:59 AM · #7 |
Originally posted by peecee:
Originally posted by lindsay:
you may want to experiment with stacking of multiple exposures to reduce random noise. camera. |
Stacking ? does this mean placing each exposure on a seperate layer and flattening ?
I assume this wouldn't be allowed in the challenges ?
Paul. |
At this time, you are correct. It is not allowed, even in the advanced editing challenges. The potential uses of the technique and it's long history in astrophotography have previously been communicated to the site council.
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02/29/2004 01:33:51 AM · #8 |
I took several shots and all of them had the same "hot pixels" (yay, I learned a new term!) in the same places. And stacking.. yeah.. that sounds like maybe it wouldn't be allowed. Same as with spot editing.. because I'm a pro at editing photos with Photoshop, but that isn't allowed in the Basic Editing rules (which I agree with, though it does present a problem for these stubborn little spots).
That first method that you mentioned.. I'll have to look into it. Although.. it may be well above my head. I've only recently learned that my camera even HAD a menu with so many options, or that you could set the date on your camera. Yes. Beginner is an understatement. But I'm learning, slowly but surely.
Thanks for all of the suggestions.. even if they don't work for this specific case, it's great to know what kinds of things are out there to try. |
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02/29/2004 04:38:00 AM · #9 |
I came across this pixel remapper. Kept having hot pixels in the same place and editing them out of my regular pics, and crop them out when I could for DPC. the program worked awesome and no problems on my coolpix 5700.
I did some before and after shots to compare if it did anything. I did shutter speeds 1/30 and 3 or 4 other shots longer up to 30 seconds. I was amazed. Be sure to read through all the info first of course. this is a on your own type of thing. the hardest part is hitting the "go ahead" button. kind of scary, but well worth it. another tip I read at DPreview (type in pixel remapping for the Nikon forum)is to have your camera somewhat cool (like 60 degrees or so). The program reads for all the hot pixels, etc. first and shows you a number of them, then you can remap (the scary part). good luck
Message edited by author 2004-02-29 05:36:51.
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