Old 08-08-2008, 06:44 PM   #1
Joe the Photog
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Default I don't understand this....

I see the grain in this shot

http://www.railpictures.net/viewreje...d=558849&key=0

but I don't understand why it's there. I shot it at ISO 100 with my XTi, either a 20 or 30second exposure. Any ideas?


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Old 08-08-2008, 07:14 PM   #2
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Sharpening the sky and resizing can make the sky seem grainy. What kind of photo editor do you use?
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Old 08-08-2008, 07:16 PM   #3
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Way to blue. Maybe the noise you see is just from the blue channel. The noise isn't that bad but the noise I see is blue when most noise is random colors. Adjust the blue channel down and re check.
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Old 08-08-2008, 07:22 PM   #4
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It might be a long exposure problem, regardless of ISO. Don't know much about it. The few times I have shot at night, I have tried to use the subtract the noise technique where the camera takes two shots, the second with a closed shutter, and internally subtracts the noise of the second from the first.

For other reasons the results were terrible and I've never looked to see how good the technology is in general.

http://www.isi.edu/~johnh/PAPERS/Heidemann01b.pdf
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Old 08-08-2008, 07:35 PM   #5
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Quote:
Originally Posted by AmericanAirFan
Sharpening the sky and resizing can make the sky seem grainy. What kind of photo editor do you use?
I do a little editting in Digital Photo Professional. Mostly a tad bit of sharpening, then brightening the shot. Then I Covert to JPEG, open with Elements and do whatever cropping the shot needs, then resize it for the web and sharpen once again.

I'll have to reopen the RAW and see if the grain is there, too.


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Old 08-08-2008, 08:06 PM   #6
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Quote:
Originally Posted by Joe the Photog
I do a little editting in Digital Photo Professional. Mostly a tad bit of sharpening, then brightening the shot. Then I Covert to JPEG, open with Elements and do whatever cropping the shot needs, then resize it for the web and sharpen once again.

I'll have to reopen the RAW and see if the grain is there, too.


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Did you make any adjustments to the noise filter settings in Digital Photo Professional? if you crank them up to high it might just do the trick.
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Old 08-08-2008, 08:50 PM   #7
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I think it must be your editing process that's causing the noise. This one's a 30 second shot with an XT at 200 ISO, that I brightened a bit, too.
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Old 08-08-2008, 08:52 PM   #8
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I've had night shots at ISO 100 and 1/2s of exposure that look grainy... And yet, the explanation is (or was) really simple: humidity.

Floating water particles that reflect what little light there is available and create that nasty effect.
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Old 08-08-2008, 09:48 PM   #9
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I get a lot of noise on my night shots with a 30D even at ISO 100. I just run some noise ninja on them first thing in the editor, but I wish I didn't have to do that. On my longer exposures (5+ minutes) I'll get thousands of hot pixels that ruin the photo. Don't really understand why there's that many either! I'm thinking of still using film for long night shots, because I think it might be something with the sensor technology in my camera, but if Canon comes out with an upgraded DSLR that gets a good rep for taking long night exposures then I might just bite the bullet and upgrade to it.

And like others said it might be something in post processing. I end up getting odd noise in the sky if I do a heavy dose of saturation on some photos.
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Old 08-08-2008, 09:53 PM   #10
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Quote:
Originally Posted by JRMDC
It might be a long exposure problem, regardless of ISO. Don't know much about it. The few times I have shot at night, I have tried to use the subtract the noise technique where the camera takes two shots, the second with a closed shutter, and internally subtracts the noise of the second from the first.

For other reasons the results were terrible and I've never looked to see how good the technology is in general.

http://www.isi.edu/~johnh/PAPERS/Heidemann01b.pdf
The technology is fine, its when you choose to apply it. It works very well when you have a 'hot pixel', when the same few pixels always tend to overheat to a red or blue spot in your photo, however, for removing grain, yeah, its not that good.
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Old 08-08-2008, 10:06 PM   #11
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Quote:
Originally Posted by Simpleboy
The technology is fine, its when you choose to apply it. It works very well when you have a 'hot pixel', when the same few pixels always tend to overheat to a red or blue spot in your photo, however, for removing grain, yeah, its not that good.
Sounds like something Ken should become aware of! If my 20D does it, his 30D will do it.
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Old 08-08-2008, 10:31 PM   #12
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Joe,

Does the XTi have, "Long Exposure Noise Reduction?" If so I hear that it works pretty good on eliminating a lot of the noise in the long exposure photos.
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Old 08-08-2008, 11:56 PM   #13
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Quote:
Originally Posted by JRMDC
Sounds like something Ken should become aware of! If my 20D does it, his 30D will do it.
It is something I'm aware of, but according to the manual with my 30D the noise reduction takes the same amount of time as the shot itself. Now for my long shots, I list the exposure length as 5+ minutes. On a lot of my shots, it's on the order of 15-25 minutes, which pretty much tanks the batteries too much to turn around and take a second 15-25 minute shot. It's also undesireable for me to have the camera out of commission that long. Also, the hot pixels seem to be random in occurrence, so on the second exposure they may not even show up. I may put on my battery grip the next time I try super long shots and experiment with the in-camera noise reduction. Maybe it will work, or maybe not...guess I'll see.
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Old 08-09-2008, 12:13 AM   #14
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Quote:
Originally Posted by ken45
It is something I'm aware of, but according to the manual with my 30D the noise reduction takes the same amount of time as the shot itself. Now for my long shots, I list the exposure length as 5+ minutes. On a lot of my shots, it's on the order of 15-25 minutes, which pretty much tanks the batteries too much to turn around and take a second 15-25 minute shot. It's also undesireable for me to have the camera out of commission that long. Also, the hot pixels seem to be random in occurrence, so on the second exposure they may not even show up. I may put on my battery grip the next time I try super long shots and experiment with the in-camera noise reduction. Maybe it will work, or maybe not...guess I'll see.
Two bodies!!!!!

I found that, the one time I tried it, shooting in the 30-60 second range, that it drove me crazy to wait that long for the second shot to crank through.
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Old 08-09-2008, 03:13 AM   #15
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I shoot tons of long exposure shots, and if you have to increase the exposure in editing, the noise becomes visible much faster than the same increase on a daylight shot.

Joe I'd increase the shutter time to get it as bright as needed out of the camera, and do not fiddle with exposure post processing. For this shot, a quick pass through noise ninja did it up quite nicely, so it's quite fixable for you.

As for the debate between in camera noise reduction, and blackcapping it, I get much results from using the in camera reduction. BlackframeNR does do a good enough job to remove hot pixels if you blackcap it, and its free.

Great capture on the lighting btw! I've yet to record a streak...

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Old 08-09-2008, 03:31 AM   #16
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They are calling for some storms tonight and Saturday. I will have to give it, long exposure noise reduction, a try also depending on how bad the storm is/gets. The one that came through last night had 60+ mph winds with a dust storm so it was not worth trying.
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Old 08-09-2008, 04:19 AM   #17
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I can see the grain in the sky, but I'm not sure what the root of it is. It doesn't just jump out at me, but I could notice it. If it's not there in DPP I would say it's a workflow thing that can be corrected. I hope you can save it it's a nice shot!
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