# Understanding noise reduction



## alaios (Jan 3, 2015)

Dear all,I am trying to understand first the "fundamentals" of noise reduction and how then I can use the tools we have to improve how an image looks likeHere are few more questions:1. What is the reason of turning off noise reduction of your camera when shooting at high isos? Can you do that better at post processing and if yes how. What means "better" though?2. What are the basic tools we have? What I can do with the sliders in lightroom and when I should try more things in photoshop?I would like to thank you in advance for your replyRegardsAlex


----------



## Tony Jay (Jan 4, 2015)

Hi Alex.

Lets look at some of these issues.
In-camera high ISO noise reduction: the reason why most of us choose to turn this off is purely practical. This process takes time - generally about double the exposure time and so when when one is doing long exposures it is a bit painful waiting for the camera to do its thing. I also use high ISO a lot for wildlife and bird photography - one loses a lot of shots with unnecessary delays.

Noise reduction is best thought of as part of sharpening and NOT as an independent topic. 

Sharpening itself should be approached as having three components. The first is *capture sharpening*. Every image needs some degree of capture sharpening to counteract the inevitable softening produced by the demosaicing process which is itself part of the process of raw file conversion. Capture sharpening is a global process affecting the entire image. The second component of sharpening is *creative sharpening*. Not all images need creative sharpening which is regional sharpening. A good example may be selective sharpening of the eye and the eyelashes in a portrait while leaving the skin with low to absent sharpening. *Output sharpening* is also important whenever an image is being prepared for either printing or web display. This type of sharpening is algorithmically distinct from other forms of sharpening in that the resolution and output medium are intrinsic to the process. In Lightroom most of the algorithms are hidden but they are actually very sophisticated.

So, how does knowing a bit about sharpening affect the approach to noise reduction. Simple! Noise reduction is really a process that has the opposite effect to sharpening. Sharpening accentuates the micro contrast alongside an edge. Lighter tones become lighter and darker tones become darker and so the edge becomes more visible to the eye. Any noise present in an image will be enhanced by sharpening
Noise reduction, on the other hand, averages out tonal differences between adjacent pixels. This gives a good result with real noise but will also reduce the tonal differences along real edges so reducing the apparent accutance of an image.

The following discussion is all about *luminance noise*. *Colour noise *will be discussed later.
*What is noise and where does it come from? *Noise is pixel-by-pixel variations in tone where there should not be tonal variation. In landscape photography the easiest place to spot noise is in the sky where large areas of tonally homogenous pixels exist (or should exist).
There are only two forms of noise that are visually apparent:
*Random noise* and *pattern noise*.
The terms themselves explain what is seen.
So where does noise come from?
Well there are three causes of noise:
*Shot noise* - shot noise is the sensor capturing natural variations in light emanating from areas in a scene that are tonally identical. Shot noise occurs with every capture. Shot noise will manifest as *random noise*.
*Read noise* - read noise occurs due to variations in how electrons stored in a sensor site (how many is determined the amount of light striking it) are converted to digital data. This analog-to-digital conversion process takes place in the electronic circuits adjacent to the sensor sites. Read noise can be visible as both *random noise* and *pattern noise*. 
*Thermal noise* - thermal noise is also a function of the electronic circuits found on a sensor. If there is a lot of activity the circuits heat up. This makes it more likely that this energy is misperceived as light energy and thus converted to digital data. Again, thermal noise, can have both *random* and *pattern *components. However, with long exposures (where the electronic circuitry really gets an opportunity to heat up) really objectionable pattern noise becomes predominant.

The noise signature of a particular sensor is set and is a cumulative function of how likely the sensor is to be affected by the various causes of noise. So, what accentuates the visibility of noise (a different concept to its actual presence)? Understanding the concept of the *signal-to-noise ratio* is important. Given that the noise signature is set for a specific sensor then the best way to reduce the apparent noise is make sure that there is plenty of signal in the form of real light striking the sensor. Any situation where the signal-to-noise ratio is low makes the noise more apparent. At base ISO having a situation where hardly any light is striking the sensor creates this situation. One has a dark image with plenty of noise apparent. lifting the shadows in post makes the noise even more obvious. If, in-camera, one attempts to remedy the dark image issue by boosting the ISO alone without increasing the actual amount of light hitting the sensor then the same problem will result. Any attempt to amplify the signal will also amplify the noise and since the signal-to-noise ratio is low the noise will be very apparent.
Long exposures will also make thermal noise more likely and so the envelope of options in which one operates with a particular camera may be limited. However, in general, the greater the signal-to-noise ratio the less apparent the noise will be.

*Colour noise* is an unwelcome but unavoidable consequence of demosaicing. Generally the default colour noise reduction applied by Lightroom is very effective at dealing with it.

In practical terms early-model digital sensors had a high noise signature and late-model cameras have very low noise signatures. Possibly the best sensors in this regard are the latest Sony sensors found in high-end Nikon cameras as well as (obviously) Sony cameras themselves. Because of this these cameras enjoy virtually absent apparent noise. It is there but very hard to notice.

In post-processing Lightroom can do an excellent job of sharpening and noise reduction.
Careful sharpening will limit the amount of noise reduction that is required.
How one sharpens depends on the image. 
Images with lots of high frequency detail need a low *radius *and a *sharpening amount* just below that which leads to visible halos. Adjusting the *detail slider* one needs to know that it is really two adjustments. Adjusting down toward zero from 50 the algorithm will implement a halo reduction process. Adjusting from 50 toward 100 will invoke a form of deconvolution-based sharpening similar to Smart sharpen found in Photoshop. *Masking* is very important in limiting the effect of the above three sliders to real edges (that do need sharpening) from noise (that one does not want to be made more apparent). In high frequency images the amount of masking that can be applied may be more limited.
Low frequency detail images are sharpened with a higher radius and more masking. In all situations adjusting these sliders should be done at 1:1. Hold down the Alt (Windows) or Opt (Mac) key when adjusting the sliders to better see the effect of any changes in monochrome.

With *colour noise reduction *go with the colour noise defaults as already recommended.
*Luminance noise reduction* has three different sliders.
The *luminance slider* controls the amount of noise reduction applied. As mentioned before this slider averages out tonal differences between adjacent pixels which results in much smoother image but with the resultant loss of fine detail.
The *detail slider *controls the noise threshold to which any noise reduction is applied. Setting this too high may preserve lots of real image detail but also the noise.
The *contrast slider* preserves image contrast and texture. The trade-off here is that high ISO images with lots of clumpy noise may have these noisy areas preserved.
Again, use 1:1 and view the image in monochrome by pressing the Alt or Opt key when editing.

Learning how to optimally use both the sharpening and noise reduction sliders takes practice - lots of it. It is difficult to generalise too much as cameras sensors, ISO, and exposure details change both the sharpening and noise reduction that can usefully and optimally be applied.

I cannot say for certain whether Photoshop, or other third-party applications, might be helpful but can only say that with late versions of Lightroom my personal experience is that no third-party applications have been required.

Tony Jay


----------



## alaios (Jan 4, 2015)

Hi,what a great answer! I guess it will take me some time to understand what you wrote and especially  the last two paragraphs on what I do in lightroom. I will read it again carefully tomorrow morningRegardsA


----------



## davidedric (Jan 5, 2015)

Now that is a post to bookmark.   Thanks, Tony


----------



## Replytoken (Jan 5, 2015)

davidedric said:


> Now that is a post to bookmark.   Thanks, Tony



I felt the same, and subscribed to the thread so I could easily find it in the future.  I want to improve my NR/sharpening techniques, and this is one resource that will help me.  IIRC, I believe that Julieanne Lost may have done a video for Adobe on this topic that was also useful.  Lots of good information.  Keepign track of it all and getting it to stick is the challenge.

--Ken


----------



## alaios (Jan 5, 2015)

Hi.just an idea.Are there examples that show how one of the lightroom sliders affect the image? I think for training reasons we need to see each component separately before we are at the state to combine all those togetherRegardsAlex


----------



## Tony Jay (Jan 5, 2015)

alaios said:


> Hi.just an idea.Are there examples that show how one of the lightroom sliders affect the image? I think for training reasons we need to see each component separately before we are at the state to combine all those togetherRegardsAlex


Perhaps one of these days I could do a video but that would be a bit time intensive and unfortunately I don't make my living doing this.
For reassurance though - I have had to learn this stuff from scratch, literally by trial-and-error.
You can see what the sliders are doing though by having the image at 1:1 and using the Alt/Opt key when manipulating sliders. You will see no more and no less than I do and you will be able make your own judgements.

Tony Jay


----------



## tspear (Jan 5, 2015)

Tony,

Great post. You explained a few things I had played with and not really taken the time to understand yet.

Tim


----------



## racehorsephotos (Jan 11, 2015)

one thing I've found in my work, sometimes shooting at very high ISO's to get a quick shutter is you need to get your white balance spot on first & foremost.
Second is I won't shoot wide open, I would at times list my ISO a stop to shoot at ƒ4, this would get rid of around 75% of in camera noise I've found.

White balance is often over looked because its so easy to fix later on.

I also use DNoise, and make profiles for each camera at each stop, go and buy an xrite color checker, it'll get you a white balance card, but you can use the color checker to make you noise profiles.


----------



## Tony Jay (Jan 11, 2015)

racehorsephotos said:


> one thing I've found in my work, sometimes shooting at very high ISO's to get a quick shutter is you need to get your white balance spot on first & foremost.
> Second is I won't shoot wide open, I would at times list my ISO a stop to shoot at ƒ4, this would get rid of around 75% of in camera noise I've found.
> 
> White balance is often over looked because its so easy to fix later on.
> ...


You post has surprised me a bit.
Perhaps I am not understanding your post but white balance plays no role in noise creation or noise reduction in raw files.
Whlte balance is merely recorded as a metadata item in the raw file header and is not actually applied to individual pixel data in a raw image.

If you have a source for your assertions please post it for our perusal - I would be interested.

Tony Jay


----------



## onyonet (Jan 11, 2015)

Just a side note, I use the Noise Reduction Luminance slider for creative effect as well. This photo was already soft focused, but I added more of the effect with this slider.http://onyonet.com/featured/apricot-tea-rose-onyonet-photo-studios.html


----------



## racehorsephotos (Jan 12, 2015)

Tony Jay said:


> You post has surprised me a bit.
> Perhaps I am not understanding your post but white balance plays no role in noise creation or noise reduction in raw files.
> Whlte balance is merely recorded as a metadata item in the raw file header and is not actually applied to individual pixel data in a raw image.
> 
> ...



Its something I've noticed over the last few years.

As a racing photographer I shot in all conditions, inc. pre-dawn with just moonlight, I've shot under lights and I've shot in all day conditions.
I've always shot raw and yes you can fit it later, but getting it right, as with everything else when shooting in the first place helps in the long run.


----------



## Tony Jay (Jan 12, 2015)

racehorsephotos said:


> Its something I've noticed over the last few years.
> 
> As a racing photographer I shot in all conditions, inc. pre-dawn with just moonlight, I've shot under lights and I've shot in all day conditions.
> I've always shot raw and yes you can fit it later, but getting it right, as with everything else when shooting in the first place helps in the long run.


I can understand your desire to shoot with the correct white balance but you seem to imply that doing so somehow impacts on noise generation. It is this part that I don't get.

Tony Jay


----------



## Replytoken (Jan 12, 2015)

racehorsephotos said:


> ...but getting it right, as with everything else when shooting in the first place helps in the long run.



I can understand it helping to streamline your work flow in post-processing, but I still cannot understand how setting a WB at the time of shot can help with noise reduction. 

--Ken


----------



## tspear (Jan 13, 2015)

Replytoken said:


> I can understand it helping to streamline your work flow in post-processing, but I still cannot understand how setting a WB at the time of shot can help with noise reduction.
> 
> --Ken



Guys, I learned the following playing around with the camera, so do not beat me up too hard. 
With the Canon 6D, if you change the white balance, it actually adjusts the scale to show if you are over/under exposed. As a result, I have found that setting the correct white balance was initially helping me set the correct exposure settings (ISO, Shutter, Aperture). As such, if you change it to indoor to outdoor, it will have you decrease the exposure dramatically which will reduce the noise.
Does that make sense?

Tim


----------



## Tony Jay (Jan 13, 2015)

tspear said:


> Guys, I learned the following playing around with the camera, so do not beat me up too hard.
> With the Canon 6D, if you change the white balance, it actually adjusts the scale to show if you are over/under exposed. As a result, I have found that setting the correct white balance was initially helping me set the correct exposure settings (ISO, Shutter, Aperture). As such, if you change it to indoor to outdoor, it will have you decrease the exposure dramatically which will reduce the noise.
> Does that make sense?
> 
> Tim


Thanks Tim - now that context has been supplied it does make sense.
For myself though - via a different approach - I have got past those issues to allow me ETTR as needed.

Tony Jay


----------



## alaios (Jan 13, 2015)

racehorsephotos said:


> ....I would at times list my ISO a stop to shoot at ƒ4, this would get rid of around 75% of in camera noise I've found.  ...


  Hi, what do you mean with that sentence "list my ISO?" Regards Alex


----------



## Tony Jay (Jan 13, 2015)

alaios said:


> Hi, what do you mean with that sentence "list my ISO?" Regards Alex


I think he means "lift my ISO" - that makes sense in the context!

Tony Jay


----------



## Replytoken (Jan 13, 2015)

tspear said:


> Guys, I learned the following playing around with the camera, so do not beat me up too hard.
> With the Canon 6D, if you change the white balance, it actually adjusts the scale to show if you are over/under exposed. As a result, I have found that setting the correct white balance was initially helping me set the correct exposure settings (ISO, Shutter, Aperture). As such, if you change it to indoor to outdoor, it will have you decrease the exposure dramatically which will reduce the noise.
> Does that make sense?
> 
> Tim



Hi Tim,

I have no intention of beating anybody up.  I just wanted to learn more, and asking questions is a good way to do so.  I do not shoot with Canon gear, so I am not familiar with their WB controls.  I would have to play around with my bodies to see if their was an impact on exposure if I manually set the WB before taking the shot.  It still sounds unusual to me, but there is a lot about life that I have yet to fuly comprehend, like the purpose of that little dangly thing in the back of your mouth. 

Thanks,

--Ken


----------

