| Author | Thread |
|
|
05/11/2006 05:47:28 AM · #1 |
noob questions from me again.
why does high ISO photos usually losses out in details? is it due to the in-camera NR? or is that just how high ISO works? If it is due to NR, then if I shoot in RAW, there should be no NR involved, right? Then why still the smeared (detail lost) appearance to ISO1600 shots?
Thanks |
|
|
|
05/11/2006 06:56:44 AM · #2 |
Either way, RAW or JPEG, high ISO shots are likely to have much less fine detail especially in the shadows just becasue of the way a digital file is exposed. Shadows in general have the least detail overall becasue they have the least tonal values. Out of 256 total values, they may only get around 20. This results in less detail in general. Add a high ISO and a lot of random noise and you'll lose even more fine detail. A good test would be shooting the same scene at all your different ISO's. The amount of detail recorded by the camera won't change, but the amont of noise added will be increasing making it much more difficult to differentiate detail vs noise.
RAW might be able to help you out some, especially in the shadow areas, but the best way to get around this is to keep the histogram when you expose as far to the right as much as possible. This keeps the shadows above the lowest stop and gives them a greater tonal range. Then you can bring them back down in PP. Shooting in JPEG you can also bracket exposures if the scene you're shooting spans the entire (or more) dynamic range of your camera i.e. highlights and shadows are getting clipped. Then just merge the exposures later in PP.
|
|
|
|
05/11/2006 01:55:10 PM · #3 |
ISO is the electronic gain of the digital sensor -- that is, how much is the energy it captures increased.
It might help to think of it as increasing the volume on a radio station; if the sigal is good and strong (good light) the volume can be increased without a problem other than deafness, but if the signal is weak (low light) increasing the volume is going to increase the noise a lot as well. Increasing the volume can make it louder (brighter) but it can't make it clearer.
Noise reduction can filter out the noise and raise the volume on just the signal (image), but that does not add detail to the image. The areas the noise was reduced from would just be silence (black) if the noise was reduced all the way, but is usually replaced by a guess at what should be there based on the surrounding signal (image).
David
|
|
|
|
05/11/2006 03:02:07 PM · #4 |
On my 30D i've noticed that the JPG captures are cleaner than RAW that i convert using Canon's software. So RAW may not actually be the best choise in some instances.
|
|
|
|
05/11/2006 03:06:39 PM · #5 |
Originally posted by Prof_Fate:
On my 30D i've noticed that the JPG captures are cleaner than RAW that i convert using Canon's software. So RAW may not actually be the best choise in some instances. |
That's true of many cams, and can be due to two things:
1.) In-camera NR applied to the JPG is more aggressive
2.) The more sophisticated demosaic algorithms in the PC-based RAW converter dig out more detail, but at the price of more readily observed noise
The reality is probably a combination of both.
|
|
|
|
05/11/2006 03:12:43 PM · #6 |
Working David.C's analogy, imagine you're listening to an audio recording. The noise level is very low. You hear all the nuances of the instruments, including the difficult-to-perceive high-frequency overtones. Now if we increase the noise level, the first thing you'll lose is those nuances, the high-frequency data that tells you about the subtle qualities of the instrument. Raise the noise level more, and you'll start to lose more data, into the high midrange. Voices, which have relatively low frequencies of a few hundred Hz, can be heard over large amounts of noise.
The same is true of images. As noise level increases, small (high-frequency) detail is the first to go.
|
|
|
|
05/11/2006 03:30:21 PM · #7 |
Another question to follow up on this:
After doing the night challenge, I've learned that long exposures also increase noise.
So what creates more noise: ISO 200 at 20 sec exposure or ISO 400 at 15 second exposure?
My guess so far is that ISO creates more noise than long exposure, but can the pros give me their input?
(sorry to hijack the thread) |
|
|
|
05/11/2006 04:03:19 PM · #8 |
On exposures over a second the canon dSLRs (20D and 30D anyway) then can do an optional NR routine - something like the same exposure with the shutter closed and then it deducts one image from the other, so the noise goes away.
I have not tried it (yet)
|
|
|
|
05/11/2006 04:12:58 PM · #9 |
Originally posted by shaggy35:
Another question to follow up on this:
After doing the night challenge, I've learned that long exposures also increase noise.
So what creates more noise: ISO 200 at 20 sec exposure or ISO 400 at 15 second exposure?
My guess so far is that ISO creates more noise than long exposure, but can the pros give me their input?
(sorry to hijack the thread) |
Not really a hijack, it's a question that is closely related to the OP's question...
We'll need to leave aside in-camera NR for the moment. If you consider a series of equivalent exposures: 40s @ ISO 100, 20s @ ISO 200, 10s @ ISO 400, and 5s @ ISO 800 they will not all have the same noise characteristics. Also, ISO 100 might not be the optimal setting for these long exposures. I've often found that ISO 200 or 400 gave best results for a single capture.
The reason for this complex behavior is that there are two components to noise:
1.) Random noise. Does not tend to get worse with longer exposures, but does get worse with higher ISO. Can be reduced by stacking multiple exposures. Not affected by in-camera long-exposure NR.
2.) Fixed-pattern noise. Gets worse with long exposures, and with higher ISO. Not affected by image stacking. In-camera long-exposure NR is very effective at reducing fixed pattern noise.
|
|
|
|
05/11/2006 04:17:03 PM · #10 |
thanks kirbic, I have also found on my D50 that 200 or 400 ISO was best for long exposure.
How does neat image come into play? Is it better to keep in-camera NR on, and do less neat image? or turn in-camera NR off and have complete control in neat image?
|
|
|
|
05/11/2006 04:21:08 PM · #11 |
Originally posted by shaggy35:
How does neat image come into play? Is it better to keep in-camera NR on, and do less neat image? or turn in-camera NR off and have complete control in neat image? |
Without a doubt, if you can afford the doubled exposure time that the in-camera NR requires, it's good to use it. If you're doing a 1-hour exposure, though, an additional hour is quite a penalty 8-O
the in-camera long-exposure NR works by taking a second frame with the shutter closed and subracting it from the real image. This cancels the fixed-pattern noise pretty effectively, without harming the image detail.
|
|
|
|
05/11/2006 04:53:02 PM · #12 |
The audiol-recording analogy is pretty accurate, except that ISO is more equivalent to amplification really. The more amplification, i.e. the higher ISO, the more of the imperfections of the CCD's process are also amplified - thus noise.
My opinion is that CCD noise is much less pleasant than CMOS noise - one of the reasons I chose Canon cameras. Whether that's just my imagination is another matter.
Most NR just smoothes out the patterns that are the 'noise' - cleverly avoiding obvious edges and the like in your image. It certainly cannot add detail, just fool you into seeing smooth where there was rough.
The most important thing though, is to find out how your camera reacts in certain situations, and to learn to uise that. Noise is not bad - in fact, noise is good. Noise is basically what makes the world interesting - it's the difference between CGI and our planet.
e |
|
|
|
05/12/2006 03:20:44 AM · #13 |
Originally posted by kirbic:
Originally posted by shaggy35:
How does neat image come into play? Is it better to keep in-camera NR on, and do less neat image? or turn in-camera NR off and have complete control in neat image? |
Without a doubt, if you can afford the doubled exposure time that the in-camera NR requires, it's good to use it. If you're doing a 1-hour exposure, though, an additional hour is quite a penalty 8-O
the in-camera long-exposure NR works by taking a second frame with the shutter closed and subracting it from the real image. This cancels the fixed-pattern noise pretty effectively, without harming the image detail. |
Following this tangent a bit farther, it is possible to do the subtraction of the black frame on the PC instead of in-camera. So wouldn't the penalty only have to be paid once for each time/ISO combination used? Once the black frame is made, couldn't it be used for every image with the same time/ISO combination?
David
|
|
|
|
05/12/2006 03:27:57 AM · #14 |
Originally posted by David.C:
Following this tangent a bit farther, it is possible to do the subtraction of the black frame on the PC instead of in-camera. So wouldn't the penalty only have to be paid once for each time/ISO combination used? Once the black frame is made, couldn't it be used for every image with the same time/ISO combination?
David |
Yes but it's one step I personally prefer to leave to the camera.
bazz.
|
|
Home -
Challenges -
Community -
League -
Photos -
Cameras -
Lenses -
Learn -
Help -
Terms of Use -
Privacy -
Top ^
DPChallenge, and website content and design, Copyright © 2001-2025 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 11/26/2025 08:48:59 AM EST.
