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DPChallenge Forums >> Tips, Tricks, and Q&A >> Shh....it's a secret -> Noise Reduction.
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12/29/2004 01:10:32 PM · #1
About to let a big cat out of a very small bag here assuming you aren't already in the know...

Just got a membership to the National Association of Photoshop Professionals and have been frantically browsing the writeups and tutorials. One of the writs impressed the heck out of me as it talked about digital noise and how to reduce it.

Of course, this method is not approved on ANY challenge except a wide-open that allows multiple exposures.

Fact: Digital Noise is never the same on a given shot. It is random.
Theory: You can eliminate the noise by using multiple shots and layering them.

1) Set your tripod and subject. This will not work on moving objects or live subjects.
2) Take 4 (yes 4) pictures of the subject without moving or adjusting anything.
3) Import all 4 pics into PS.
4) Shift-Drag each onto one so there are four, snapped-to layers.
5) Set opacity of background to 100%, layer1 to 75%, layer2 to 50% and layer3 to 25%.
6) Check for noise and have someone take a picture of you when you realize what you see.

Happy Coloring!

Message edited by author 2004-12-29 13:11:40.
12/29/2004 01:38:25 PM · #2
jejeje™

You spilled the beans... I been doing this for years. Less need for it now we have better sensors, so I have gotten away from it, but it was a godsend with the 2 Mp cams. And yes, it's verboten in our challenges, more's the pity.... Too bad, really, since in advanced editing we can clone off as many layers as we need, and this is functionally the same thing as stacking layers.

I've experimented with stacking layers and adding different (small) amounts of random noise to each, then blending them thru transparency, but it hasn't worked especially well.

Robt.
12/29/2004 01:43:12 PM · #3
any fisheye tutorials?
12/29/2004 01:50:42 PM · #4
stacking layers of the same shot wouldn't work?
12/29/2004 01:54:09 PM · #5
Same shot would have the exact same noise pattern and would not create a noise cancellation overlay. I guess the idea here is that the transparency stacks the real color over/under the noise more times than it stacks the noise itself.

Message edited by author 2004-12-29 13:55:00.
12/29/2004 01:54:14 PM · #6
if you did that sher..wouldn't it just be noise stacked in all the same places?

(ie. I'd love an answer to your question too!)

edit: looks like I posted a few seconds too late. :) The answer is what I suspected!

Message edited by author 2004-12-29 14:00:28.
12/29/2004 01:54:50 PM · #7
Originally posted by sher9204:

stacking layers of the same shot wouldn't work?


No, because it is the same shot with the same noise distribution.
The point is that the noise from separate images of the same scene cancels out if you use the stacking method. It is a technique that has been used in sound processing for decades.

It has been a public secret in the Sony forum at dpreview for years.
Look here at an image by Shay Stephens. He has been using the technique and probably also used it on that image.

By the way,here is a link that shows the correct (?) percentages to be used.

Message edited by author 2004-12-29 14:02:59.
12/29/2004 02:01:51 PM · #8
It is used quite a bit in AstroPhotography (photographing the stars, planets, etc). It is called "stacking".
In Astronomy they treat digital noise very seriously as some "dot" could be seen as another "star" when it is actually just noise. So ideally you want to completely eliminate it.
You can also use "stacking" with video footage to get very good quality pictures of e.g. the planets from a simple webcam. Simply stack 300+ frames together with some special software you can download off the Internet. not high-res stuff, but miles better than most of the serious telescopes could produce a few years ago.
"Stacking" works well with the stars and planets of course as they normally don't jump around too much...

Alternatively you can cool down your digital camera to eliminate all noise from the sensor as described here. :-)
As he describes it:
"As we all know, the dark noise of the camera chip is reduced by a factor of about 2 for every 6 degrees Celsius reduction in the camera temperature. This equipment is able to reduce the temperature of the camera by 24 degrees below ambient. Thus at room temperature, 22 Celsius, the camera can be cooled to 0 Celsius. This gives a reduction in the dark noise generated by the camera of about 16 times."

And this method is allowed by the challenge rules!! LOL
12/29/2004 02:09:03 PM · #9
Originally posted by Arcanist:

Same shot would have the exact same noise pattern and would not create a noise cancellation overlay. I guess the idea here is that the transparency stacks the real color over/under the noise more times than it stacks the noise itself.


gotcha...i understand the concept now.

sorry...my brain isn't functioning on the higher levels today. :)
12/29/2004 02:15:53 PM · #10
Its also quite a nice technique for capturing waterfalls. Each droplet gets forozen in a different place. This means that the areas where the droplets are close together become silky smooth, whilst the areas of wider spaced droplets become very much richer.

I used to do it with film cameras using multiple exposure and reducing the exposure values way down.

Have a play next time you go to the local waterfall, take your tripod and trip off 8 identical (almost) shots..
12/29/2004 02:23:12 PM · #11
Originally posted by willem:

By the way,here is a link that shows the correct (?) percentages to be used.

Man, I tried to read that thread, but my "inner monologue" started saying "blah, blah, blah...NeatImage" Isn't this just the kind of stuff a tool like NeatImage already does for you? What advantage does this have other than keeping everything in photoshop (which can be done with the full version of most noise reduction plug-ins)?
12/29/2004 02:32:43 PM · #12
Originally posted by bledford:

Man, I tried to read that thread, but my "inner monologue" started saying "blah, blah, blah...NeatImage" Isn't this just the kind of stuff a tool like NeatImage already does for you? What advantage does this have other than keeping everything in photoshop (which can be done with the full version of most noise reduction plug-ins)?


For most photographs, no advantage at all. Use NeatImage.

For things like Astronomy, big difference. That small dot that NeatImage thought was as a bit of noise was actually a new comet, heading straight for planet Earth. Too bad you missed it... :-)

12/29/2004 03:17:52 PM · #13
Originally posted by Falc:

Its also quite a nice technique for capturing waterfalls. Each droplet gets forozen in a different place. This means that the areas where the droplets are close together become silky smooth, whilst the areas of wider spaced droplets become very much richer.

I used to do it with film cameras using multiple exposure and reducing the exposure values way down.

Have a play next time you go to the local waterfall, take your tripod and trip off 8 identical (almost) shots..


Just thought I'd put up an example of a stacked waterfall - this one is 10 images stacked as described above.

' . substr('//images.dpchallenge.com/images_portfolio/5354/thumb/131483.jpg', strrpos('//images.dpchallenge.com/images_portfolio/5354/thumb/131483.jpg', '/') + 1) . '
12/29/2004 04:07:58 PM · #14
Originally posted by rudidl:

Originally posted by bledford:

Man, I tried to read that thread, but my "inner monologue" started saying "blah, blah, blah...NeatImage" Isn't this just the kind of stuff a tool like NeatImage already does for you? What advantage does this have other than keeping everything in photoshop (which can be done with the full version of most noise reduction plug-ins)?


For most photographs, no advantage at all. Use NeatImage....


Beg to differ... if you ever try it you will see that there is a huge difference. The only downside is that any motion at all will result in some funkiness. If motion blur is OK. like falc's waterfall, then this technique can provide some awesome results.
There's a second type of noise that's not addressed by this technique. It's known as fixed-pattern noise, and as you might guess, it has the same general pattern shot to shot. Because of this property, you can get rid of much of it by subtracting a "dark frame", essentially a pic taken with the same setings but the lens cap on. Serious astrophotographers do both dark frame subtraction and averaging. Also note that the 20D and I believe the D70 will do dark frame subtraction in-camera.
12/29/2004 04:56:30 PM · #15
Originally posted by kirbic:

Beg to differ... if you ever try it you will see that there is a huge difference. The only downside is that any motion at all will result in some funkiness. If motion blur is OK. like falc's waterfall, then this technique can provide some awesome results.


Thanks! So we learn new things every day.

I have used both techniques with some astronomy photos, but have never tried it elsewhere. Cool, something new to play with the next few days! :-)
12/29/2004 04:59:12 PM · #16
Rudidl,

TRY it; it's not hard. Set up a shot of something static with a tripod, shoot it 4 times. Make one composite image layering all 4 images as above, make another staright image from one exposure, and then clone that and use neat image on it.

Blow 'em all up like 800% and compare. You'll be stunned. I'm not kidding.

(robt)

12/29/2004 04:59:13 PM · #17
Originally posted by kirbic:

Originally posted by rudidl:


For most photographs, no advantage at all. Use NeatImage....


Beg to differ... if you ever try it you will see that there is a huge difference. The only downside is that any motion at all will result in some funkiness. If motion blur is OK. like falc's waterfall, then this technique can provide some awesome results.
There's a second type of noise that's not addressed by this technique. It's known as fixed-pattern noise, and as you might guess, it has the same general pattern shot to shot. Because of this property, you can get rid of much of it by subtracting a "dark frame", essentially a pic taken with the same setings but the lens cap on. Serious astrophotographers do both dark frame subtraction and averaging. Also note that the 20D and I believe the D70 will do dark frame subtraction in-camera.

Cool to know! Seems like an aweful lot of Photoshop work though. I guess I'll start worrying about that when I take the sort of pictures I can retake 5 times in a row *and* I'm worried about random pattern noise. LOL.

Message edited by author 2004-12-29 16:59:30.
12/29/2004 05:14:30 PM · #18
I believe that there might be another method for reducing noise but I haven't investigated it yet (it has been on my to-do list). The idea is to manually set your camera to the exact same settings as a photograph who's noise you want to reduce and then take a photo with the lens cap on (maybe even wrap the camera with a towel to make sure there is no light entering the lens) then combine the photo with the main photo via layers. I'm not sure what layer blending properties to use. It is supposed to be the same technique as the dark frame subtraction method that many cameras utilize on slow exposures. What I like about this technique is that you could take your second photo at any time afterwards. The one x-factor that could pose a problem (if this technique works at all) is the temperature that you are shooting in. Different temperatures can effect the amount of noise in a photo (colder means less noise, warmer means more noise, relatively). It sounds interesting and if I try it out I will let you know whether it works or not. Maybe someone else has already tried this and can comment.

T
12/29/2004 05:15:55 PM · #19
It's actually not hard at all to do. If you make no other adjustments, you can slap this baby together in 2-3 minutes. No tools required for assembly, LOL. It gets tougher when you're using adjustment layers. The easiest way is to clone off the 4-layer base image to a new file, flatten the layers, and treat that as your original for other effects.

(robt)
12/29/2004 05:18:47 PM · #20
Remember that in Photoshop CS Camera RAW has a noise reduction slider, you can adjust colour noise and luminance noise, it does a pretty good job that Noise Ninja or Neatimage can improve on.
12/29/2004 05:40:57 PM · #21
Originally posted by bledford:

Isn't this just the kind of stuff a tool like NeatImage already does for you? What advantage does this have other than keeping everything in photoshop (which can be done with the full version of most noise reduction plug-ins)?


It preserves all detail.
12/29/2004 06:27:42 PM · #22
If you generate two (or more) versions from a RAW file with slightly different settings, can you affect the noise distribution? If so, you could DPC-legally stack those.
12/29/2004 06:30:14 PM · #23
Thanks JD this stuff is gold!!!
12/29/2004 06:30:22 PM · #24
Originally posted by GeneralE:

If you generate two (or more) versions from a RAW file with slightly different settings, can you affect the noise distribution? If so, you could DPC-legally stack those.


Nope. You can affect the amplitude of the noise, but not it's spatial distribution (pattern). The overall idea is the ol' axiom that "entropy cannot decrease", that is, you can't pull information from noise, order from chaos. you need to add information, and that means a true second exposure. There truly is no free lunch.

Message edited by author 2004-12-29 18:31:18.
12/29/2004 06:32:51 PM · #25
Right, detail. Look at it this way; when you use neatimage, it makes a "determination" whether a given pixel is noise or information. If it decides it is noise, it then interpolates information from neigboring pixels and overwrites the noise.

Now, take 5 separate, identical exposures in your camera. In each the noise, which is random, will be different. Imagine a program which analyzed each of these layers and, based on "majority: rules, assigned a "noise" or "information" tag to eaach pixel: this would be way more accurate, see? Id 3 or 4 of the images agreed a given pixel was information, it would get tagged that way. Imagine a composite image, cimnputer generated, of the highest "vote getters" among the pixels. This would be very noise free, and then neatimage could work on THAT if it wanted to and interpolate away the remaining, slight noise.

Now, that's not what we're doing, of course. To my knowledge no such program exists at the photoshop level. However, by layering together the various exposures at varying degrees of transparency, we are "overwriting" a LOT of noise with "real" information instead of interpolations of what ought to be there.

Thus, more detail is preserved.

I use a 3rd party jpeg repair tool that I love, and it produces some fascinating effects if you dial it way up, blocking out monotone areas and leaving texture in complex areas. It works on the same principle
as neatimage, I believe.

Robt.


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