# How Is Noise Created?



## Buszaj (Jun 3, 2008)

Well, most of us know that when you increase the ISO, you get more noise. I was wondering, why does this actually happen?

Thanks


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## Alex_B (Jun 3, 2008)

when a signal is created from a sensor pixel, then there is always noise.

This noise depends on the pixel, on its temperature and whatever.


If we now have a weak signal since there is not much light, then we have a bad signal to noise ratio (relatively small signal, but lots of noise). If we have more light, then that ratio becomes better, since the signal increases but the noise remains more or less the same.

If we now increase the ISO, this only means that we amplify more, hence _both _signal _and _noise are amplified. With a bad signal to noise ratio we need to amplify more (higher ISO) to get the same signal strength. But more amplification then means more noise since the signal to noise ration remains the same.


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## Alex_B (Jun 3, 2008)

Buszaj said:


> you get more noise (CA).



But to my knowledge the acronym CA usually refers to chromatic aberration. This is only related to the lens/ the optical system, and not to the ISO.


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## ann (Jun 3, 2008)

it is my understanding it is the increase in the electical charge that has to be increase to enable the sensor to record the image at the higher ISO's.

for instance, with film, the size of the silver particles are increased in size to make the film more light sensitive, which translates into grain.

with a sensor, there is no way to change the size to make it more sensitive so the electrical impulse that records the images is boosted, which ends up as noise (grain)

there may be a more complicated answer and i am sure somone here can expand on my answer.


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## Socrates (Jun 3, 2008)

ann said:


> it is my understanding it is the increase in the electical charge that has to be increase to enable the sensor to record the image at the higher ISO's.
> 
> for instance, with film, the size of the silver particles are increased in size to make the film more light sensitive, which translates into grain.
> 
> ...



How about a more simplified answer?
Think of audio and, specifically, the background sound (noise) in your environment.  The louder it is, the louder you must shout to overcome it.  Just as audio noise exists everywhere on earth to greater or lesser degrees, so does electrical noise.  Just like sound, the greater the electrical noise, the greater the signal must be to overcome the noise.  Hence, the S/N (Signal-to-Noise) ratio that Alex mentioned.


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## Buszaj (Jun 3, 2008)

Thanks for the answers, I get it now.



Alex_B said:


> But to my knowledge the acronym CA usually refers to chromatic aberration. This is only related to the lens/ the optical system, and not to the ISO.



Ohhhh, I see. Learn something new everyday....I said that because I heard that noise is also referred to as CA, but I guess ISO noise isn't the same.


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## JerryPH (Jun 3, 2008)

Buszaj said:


> Well, most of us know that when you increase the ISO, you get more noise (CA). I was wondering, why does this actually happen?



Just wanted to mention... CA (chromatic aberration) is an undesirable  lens effect, not high ISO noise related.


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## ann (Jun 3, 2008)

socrates i thought that was a simple answer, i thought of the audio example but it wasn't along the same lines you gave, which certainly makes sense as well.


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## Socrates (Jun 3, 2008)

ann said:


> socrates i thought that was a simple answer, i thought of the audio example but it wasn't along the same lines you gave, which certainly makes sense as well.



:hug::


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## cdanddvdpublisher (Jun 3, 2008)

Socrates said:


> How about a more simplified answer?
> Think of audio and, specifically, the background sound (noise) in your environment.  The louder it is, the louder you must shout to overcome it.  Just as audio noise exists everywhere on earth to greater or lesser degrees, so does electrical noise.  Just like sound, the greater the electrical noise, the greater the signal must be to overcome the noise.  Hence, the S/N (Signal-to-Noise) ratio that Alex mentioned.



that's a great explanation


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## Socrates (Jun 4, 2008)

cdanddvdpublisher said:


> that's a great explanation


Thanks.


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## Bifurcator (Jun 4, 2008)

I guess we're talking about grain type noise?

I always thought it was that the sensitivity of each photocite (photo sensitive cell) is different from one to the other. When you amplify the signal coming from them (by increasing the ISO) you are amplifying the differences causing one cell to register very high and one to be normal (average) or too low.

Consider the simple experiment.

Givens: 

The light entering the lens = 3 
A recording of 0 registers as black (IRE 0)
A recording of 32 registers as 100% white.
You have a 3 pixel CCD 
For this example let's pretend that an ISO amplification of 100 is 1x, an ISO amplification of 200 is 2x and so on.
You take 3 sample test shots at ISO 100, 400, 800.

At ISO 100 the three photocells register 2,4,2 respectively (one photocell per pixel). As seen in a grey scale image there's very little difference between the three pixels.

At ISO 400 the three photocell signals are recorded as 8, 16, 8 respectively. Now the difference is very noticeable when viewed in the grey scale image.

At ISO 800 the recording is 16, 32, 16. The relative difference in visual perception when viewing a gray scale image is also high enough here to be called noisy.

The CMOS process produces generally more sensitive cells (faster) and with greater grid uniformity so less noise.

The non-uniformity of light as particles plays a roll here too (where one cell may receive more or less than the average number of photons in a given source) but I always thought it was a minor factor compared to the surface imperfections that form the photosensitive substrate, their electrical response variation, the optical inequalities from one micro-lens to the next, and the roll that amplification plays - as explained above.

No?


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## Garbz (Jun 4, 2008)

Well this all explains how noise is amplified but not where it comes from. Bifurcator that isn't correct, if it were taking 2 photos and averaging the result wouldn't halve the noise. But it does because noise is a random Gaussian distribution.

Ok so starting at the analogue digital converter and the signal amplifier. Both have noise determined by a few things such as external interference, noise on the powersupply (voltage regulators in consumer electronics regulate by switching on and off some 200000 times a second), and by Johnson noise (this is thermal noise relating to resistive elements and temperature, it exists it can not be reduced without reducing the resistance in the path).

Back a bit further we have Shot noise which dominates the amplifier. This is fluctuation in the movement of electrons through a conductor. It gets worse in a semiconductor like a MOSFET amplifier (there's one of these under each photo detector cell on your sensor).

The photo detector itself produces noise too, normally three types. Dark Current, surface fluctuation, and statistical gain. Dark current is when random thermal changes generate electron hole pairs and generate current even when no photon has hit the sensor. Surface fluctuation is a result of manufacture, photos taking a different path into the detector may not generate an electric charge than another photon. And Statistical gain occurs in avalanche devices (though I am not sure if these are used in cameras.)

All the way back there's one more source, quantum noise of the photon, which in it's most basic form is Shot noise applied to a photon instead of an electron, and in more complicated analysis is dependent on the uncertainty of the E-H field amplitude and phase of the light entering.

Now over to you Socrates so other people who didn't take 4th year photonics at uni can understand this too.


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## Bifurcator (Jun 4, 2008)

OK, what specifically is incorrect? Both explanations seem to mesh to me. Yours adds some other variables and identifies a few more sources, and of course is more specific with nice technical aesthetics, overall superior and... 

But aren't we saying kinda the same things?

BTW, I didn't say anything about taking two photons and averaging them. I used the word "average" only to identify a general light level (or photon quantity if you will) existing outside the camera.


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## dEARlEADER (Jun 5, 2008)

Garbz said:


> Well this all explains how noise is amplified but not where it comes from. Bifurcator that isn't correct, if it were taking 2 photos and averaging the result wouldn't halve the noise. But it does because noise is a random Gaussian distribution.
> 
> Ok so starting at the analogue digital converter and the signal amplifier. Both have noise determined by a few things such as external interference, noise on the powersupply (voltage regulators in consumer electronics regulate by switching on and off some 200000 times a second), and by Johnson noise (this is thermal noise relating to resistive elements and temperature, it exists it can not be reduced without reducing the resistance in the path).
> 
> ...



hmm.... ya I think I'll stick with Socrates audio explanation.... more geared to my neanderthal way of thinking....

wait till Helen chimes in...... that will officially blast this thread into the beyond the basics forum...

edit:
****Oooops..... I'm in the Beyond the Basics Forum..... What the hell am I doing in here??****


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## Garbz (Jun 5, 2008)

Bifurcator said:


> OK, what specifically is incorrect? Both explanations seem to mesh to me.



Actually you're right, sorry. Re reading it, it's not incorrect it just tells half the story. You're explanation essentially covered surface fluctuation, and differences in FET gain due to manufacturing.

But camera noise is typically made of random elements which make noise unpredictable. What I was saying is if you take 2 high iso or long exposure images and then put them through some software algorithm that averages each pixel value the type of noise you mentioned would be unaffected. However I believe the random noise I was talking about would contribute more than manufacturing error (opposite of what you said  ) which is backed up by the fact that if you take two noisy images and run them through an averaging program (like Image Stacker) the noise is significantly reduced.

It's actually hard to say if this has always been the case. Especially on old cheap cameras I'm inclined to believe that manufacturing error would have contributed much more, but it was likely masked by lack of technology in the photosensor department. Or in fact if it will be in the future. There are all sorts of creative methods these days of reducing noise including changing the order in which pixel rows are read out so they do not pickup interference from each other, positioning amplifier elements directly under the photosensor to reduce noise along wiring running between sensors (I believe Olympus leads this development), etc.

Actually, and this is just my brain playing weird, the errors you're talking about could in theory be mapped out completely by software since they are essentially constants. I wonder if any companies actually do this...


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## Bifurcator (Jun 5, 2008)

No prob-a-lem-o! You for sure, know allot more than I do about this topic - that's rather obvious - I was just trying to get straight what I thought I knew. I did neglect the various components that  manipulate the current in one way or another as I assumed the affects were negligible relatively speaking. It's interesting to find out that the condition of the current itself naturally or via the disruption caused by the various components, is erratic enough to be much of a contributing factor to what we ultimately see as image noise. I figured there was some of that going on but maybe like <15% of the total factors. Hehehe it's much easier to visualize quiet flawless circuits than it is to actually build them. What one may visualize as a calm steady flow is on a nano scale, a terrible turbulent and chaotic storm. 

Also just to be clear tho, I wasn't blaming everything on the manufacturing process but was attempting to include the idea of natural material imperfections, roughness,  etc. (and effects it has on the electrical charge current (ECC)) - which such texture if you will, is probably distributed in gaussian or close to gaussian random patterns. 

So, overall you're saying that the noise present in the ECC resulting from component interaction (both upstream and down) is way more a factor in the production of noise (recorded as image noise) than the electrical properties of the CCD itself with all it's variances (burst, flicker, etc.) and imperfections?  And that combined with naturally occurring "micro-scale" line noise or shot noise, is the major culprit? Heheh, can you tell I'm used to larger scale circuits? 

In any case your explanation was a beautiful one. Claude Shannon would be proud! 

Your images rock too btw!


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## Garbz (Jun 6, 2008)

Hey thanks for the compliments. This is actually a fluke that I know this. My thesis advisor insisted I take a course on Photonics this semester since I'm working with lasers, and I hope what I said is right because my exam is on Wednesday. 

Yep we're basically on the same page now. Just that the Electrical properties of the CCD contain random noise generating elements too (Dark Current as described above). I'm a bit of a microelectronics guy and my thesis is on low-noise circuit amplification (trying to get a 1microV signal from a laser to a usable level) which is why i'm full of this useless information.

To everyone else who didn't understand what I'm talking about: 

I'll revert to Socrates' example. Lump all the fancy terms I used into the sound made by a highway, and then assume the photo detector is made up of a bunch of people standing on the opposite side of a football field shouting at you.

The fact that noise varies so much from camera to camera is testament to the fact that even the slightest change not to the circuit, but even to the layout (one cable from the sensor being close to another signal) can dramatically affect performance of such an insane precision system.

You think the D3 costs a lot, you should check out the sensors used for some precision work often in research labs. The sensing unit and computer interface easily breaks the $10000 mark and then some.


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## KD5NRH (Jun 6, 2008)

It comes from the firmware of the camera; there haven't really been any advances in digital cameras in several years now, they just enable a few more features, turn down the noise a bit, and repackage the same chassis every few months.


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## Garbz (Jun 6, 2008)

So companies just spent squillions on sensor redesign as a tax writeoff?

Ahh well time to whip out my sisters P&S I'm sure I can firmware hack it to the D3 level.

Makes me wonder why don't they turn the noise off completely. They'd instantly corner the market and make ooodles of cash. Canon could release a Canon 1DMkIII-b with the noise turned off and Nikon people would flock to them.

Brb the fairies outside are harassing my pet unicorn.


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## dEARlEADER (Jun 6, 2008)

Garbz said:


> So companies just spent squillions on sensor redesign as a tax writeoff?
> 
> Ahh well time to whip out my sisters P&S I'm sure I can firmware hack it to the D3 level.
> 
> ...


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## KD5NRH (Jun 7, 2008)

Garbz said:


> So companies just spent squillions on sensor redesign as a tax writeoff?



Why not?  Look at the computer industry and all the "advances" that were nothing but marketing ploys to sell the same thing under a new name.  It works, too; look how many people owned 486DLCs back in the day, and it was just a slightly hotrodded 386, with a name intended to make it sound like a 486DX.



> Makes me wonder why don't they turn the noise off completely. They'd instantly corner the market and make ooodles of cash. Canon could release a Canon 1DMkIII-b with the noise turned off and Nikon people would flock to them.



Yes, but then, once everybody has one, where would they get more money?  By turning it down a bit every release, they guarantee themselves repeat customers.

It's just like changing lens mounts from time to time; there was nothing wrong with the old ones, but if they let you use all your old lenses on the new body you won't be so quick to buy a bunch of new ones.


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## Garbz (Jun 7, 2008)

:lmao: This is most entertaining. Even more so than finding out what O|||||||||O's nickname stood for this morning.

Let me explain the difference between consumers and prosumers. The former will eat every line you feed them. You are right Canon intentionally cripple their P&S cameras. There's custom written firmware out there to enable high ISO, manual controls, histograms, better JPEG compression, RAW support, woopse noise wasn't on the list, guess they haven't figure out how to write firmware yet that doesn't introduce noise. This works for that demographic alone.

Professionals and Prosumers on the other hand don't get caught on upgrade cycles. They get stuck on accessories which have a huge premium on them. I mean if we could turn off noise in software, we'd have perfect photo detectors. The price of quantum data transmission would plummet.

Same principle applies to computers. This **** may work for creative labs in an industry where they've hit the brick wall of the sound is bloody good enough how do we sell more products to consumers who don't need 20.5 surround sound, or back in the day where people didn't need the faster computer because most software was small enough to fit on 2 floppy discs, but can you imagine if IBM was found to be intentionally crippling their Power5 processor? Their stocks would faceplant into the ground.

Anyway gtg reboot. I just firmware updated my Athlon 800 to support 64bit code and 2 cores..


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## Bifurcator (Jun 7, 2008)

Garbz said:


> :lmao: This is most entertaining. Even more so than finding out what O|||||||||O's nickname stood for this morning.


 The last thing he saw before it was "lights out"? Rolls Royce front grill? A man with too many noses? Come'on spill it! 





> most software was small enough to fit on 2 floppy discs,



You young kids... I swear!  The proper phrase is "...small enough to fit on a punch-card" or if you wish to be downright  decadent "...small enough to fit on a spool of paper-tape." "Floppy disk" is way to modern a term! Especially when almost all applications still do indeed fit on 2 floppies.  



> Anyway gtg reboot. I just firmware updated my Athlon 800 to support 64bit code and 2 cores..



Sweet! Did you need superglue or a screwdriver? Hehehhehehe... This thread did turn kinda funny. I can see why some people might think that tho with the noise thing. These camera companies do pull lots of rather obvious and embarrassing boners very similar to KD5NRH's assertions. Alas unfortunately, it isn't the case. Although I suppose they *could* incorporate better noise reduction algorithms. Some of the skews they go with are downright archaic.


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## Garbz (Jun 7, 2008)

Very close. http://www.thephotoforum.com/forum/showthread.php?t=125838 He's down on post 24. Still it's classic. I never made the connection.

Punch cards? I heard about them. Theres an old urban legend at my uni that before optical magnetic and holographic data storage, people just made holes in paper. Sounds absurd to me. 

Yeah NR algorithms themselves are lacking. But then even in some commercial applications they are too. The D200 NR is pretty poor but I still think it beats Lightroom's. Well that's what Noise Ninja is for


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## Bifurcator (Jun 7, 2008)

Ah, so I got it right with the 1st one. 

Hey, I only just threw out my PT reader last year!  Seriously! And I've been kicking myself for it ever since too. I should have kept it... it was neat looking. Solid cast aluminum too - thing weighed a ton but only the size of about 1.5 DSLRs 

True -  they have to keep us busy doing something. Right?


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## KD5NRH (Jun 8, 2008)

Bifurcator said:


> Solid cast aluminum too - thing weighed a ton but only the size of about 1.5 DSLRs



Probably worth a fortune as scrap, then.  I think I still have an 8" floppy drive laying around somewhere in storage.


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