What makes a photo 'grainy/noisy' ?

MiiLovely · Aug 1, 2012

(hopefully I am posting this in the right section.. if not I am SO sorry!)

Anywho on to my question.. what makes photos grainy/noisy? Im just starting out and I know I havent got the hang of my camera settings yet but I was just wondering what I should focus on to get rid of the grainy-ness and most of the noise in my photos. Is it a certen setting Im dont have properly with the iso and appature? Or is it the kit lens I am using? (Im going to guess its the type of lens Im using but Id like to know exactly what makes a photo nice and sharpe and clean) thanks!

rexbobcat · Aug 1, 2012

ISO is the main culprit usually. Lower ISOs have less noise/grain, and higher ISOs have more.

Also; in digital photography it's called noise and in film photography it's called grain, usually.

enzodm · Aug 1, 2012

Plus, it is more evident in dark areas, so try to expose well your pictures, to avoid increasing brightness in postprocessing. Since you mention also "sharp", that's another story (motion blur, wrong focus, etc).

SoCalTiger · Aug 1, 2012

Also, if you haven't figured this out already... if you are shooting in low-light conditions, you/your camera will need to up the ISO accordingly especially if you are just using the kit lens. So if you are seeing noise under these conditions, that is definitely the culprit. Also pay attention to not underexpose as pointed out in the post above mine.

MiiLovely · Aug 2, 2012

Thank you everyone, I completely forgot that even though my camera is a good camera it isnt magical and it needs helping producing good photos lol (ie good lighting!) lol

scorpion_tyr · Aug 2, 2012

Yep, high ISO is the number 1 cause. Other causes can be a bunch of megapixels packed into a small sensor like point and shoots with a little bitty sensor and 18 MP's. Extremely long shutter speeds can also cause noise... usually only when it's more than 2 minutes or so. Some atmospheric conditions can also cause noise from light reflecting off dust or water vapor in the air that you don't see with your eyes.

Phototripper · Aug 2, 2012

A high ISO is probably your culprit, but the other posters are hitting on good points as well. Sometimes noise is avoidable, but there are tools that can help a little in post processing. I use Noiseware Professional and Noise Ninja to reduce noise and they work pretty well to eliminate mild amounts of noise. A good tool that I have found that helps when trying to determine the effects of ISO, Aperture, and Shutter Speed is the CameraSim, by Jon Arnold. There is a free online version at CameraSim | SLR Photography Demystified. Go check it out if you want to practice with your settings in a simulated environment.

KmH · Aug 2, 2012

Digital photos don't have any grain. There are several kinds of digital image noise - Image noise - Wikipedia, the free encyclopedia

Half of all a digital photograph's luminosity data is in the brightest stop of exposure. Which is the basis for ETTR - Expose-To-The-Right. Exposing to the right - Wikipedia, the free encyclopedia

ETTR

http://wwwimages.adobe.com/www.adob...e/en/products/photoshop/pdfs/linear_gamma.pdf

http://wwwimages.adobe.com/www.adob...ly/prophotographer/pdfs/pscs3_renderprint.pdf

Derrel · Aug 2, 2012

Jeopardy answer: "What is the Nikon D2x when shot at ISO 640, Alex?"

MLeeK · Aug 2, 2012

I've so missed adding my two cents...

They've got you covered, ISO is the biggest culprit. HOWEVER, don't sacrifice exposure to keep your ISO low. If you take an image at ISO 100 that's underexposed and bring it up in post it will infinitely more noise than an image that is properly exposed at ISO 800. Or higher. You can use the full range of ISO on your camera if you properly expose for it. Ultimately underexposure is more often the culprit than the ISO.

unpopular · Aug 2, 2012

Noise is generated any time noise, which is always present, out weighs signal. When you make an exposure, the sensor only has available the light which is accumulated. The data which is collected is amplified, either in the analog or digital domain. When you increase ISO, you are increasing the sensor's analog gain. When you make a photo "brighter" on the computer, you are amplifying digitally. When you increase the ISO, you need less exposure to meet a given signal. When you decrease it, you need more. More exposure=more signal to drown out the noise.

Imagine if your room mate was listening to a Twisted Sister CD really loudly. You want to listen to your new Smooth Jazz CD, so you put on the headphones, if you don't have sufficient volume (signal) you will hear more of the noise (butt rock). It's not that you've decreased the amount of butt rock, you've simply provided more signal to drown out the noise.

However, there is no means to discriminate between what is noise and what is data which reflects the scene. So the simplest answer is that a noisy image is one which lacks exposure. Gain, whether analog or digital is like turning up both the Twisted Sister album and your Kenny G album at the same rate. You might hear Kenny's sexy sax more readily, but not any more clearly.

High ISO is one source of shortfall in exposure that results in noise. The other is color. CCDs are more sensitive to red than they are to blue light, often by about 1.3 stops. This isn't so much a problem when, say, the subject is a warm sunset where the color is left uncorrected. However, the moment that you try to compensate for this in white balance, some amount of noise is to be expected, especially if the circumstance is complicated by insufficient exposure. Any time you have a severe color cast you can expect noise, but it is especially problematic in warm scenes where the already disadvantaged blue channel is under exposed.

A second source of noise is so-called "Dark Current" noise which exists as the CCD heats up with longer exposures. It is possible, though perhaps unlikely, that noise can exist if the ambient temperature is very hot (in excess of 105°), and certainly high ambient temperature may have an effect on long exposure noise. It may be a good idea to avoid higher ISO's in very hot weather, though I don't have any real evidence to back this up.

unpopular · Aug 2, 2012

MLeeK said:
HOWEVER, don't sacrifice exposure to keep your ISO low. If you take an image at ISO 100 that's underexposed and bring it up in post it will infinitely more noise than an image that is properly exposed at ISO 800.

Furthermore every sensor has a native sensitivity which may or may not be it's lowest ISO. While my camera has lowest overall noise at ISO 100, I have greatest dynamic range at ISO 200. I've found that shooting at ISO 200 requires less shadow recovery than at ISO 100. I'd rather have better shadow detail at ISO 200, even at the expense of a little more noise.

TCampbell · Aug 2, 2012

One last comment. Using high ISO is spot on. In the vast majority of cases, this is the reason why you get "noise" in an image.

But there are a lot of nuances if you shoot JPEG. The camera general has built-in algorithms to reduce the noise. The easiest way to do this is to look for aberrant pixels by comparing them to neighboring pixels and then averaging the color values to decrease the noise. The camera will do this automatically. BUT... it has a rather undesirable side-effect of "softening" the image -- so you might not see "noise" in the image (usually you will... it just wont be as severe) but you'll notice that the image quality isn't as good (you'll lose detail).

The aggressiveness of the camera's de-noising algorithms are typically tied to the ISO. For example... your camera probably wont do any de-noising at all if you shoot at low ISO speeds (say... 100-400). But then it'll kick in mild de-noising as soon as you hit ISO 800 (btw, I am making these numbers up to convey the point... how aggressive a camera will be and when it kicks in is entirely dependent on your camera's processor.) But as a result of the de-noising kicking in, you might actually notice that ISO 800 looks less noisy than ISO 400 -- even though that *should* not be the case. If you really inspect that image closely, you'd notice that although the ISO 400 image looks like it has more noise... it also has more detail.

If you shoot in RAW, none of this applies as the camera will not perform any de-noising in the camera. That's no problem because most photo processing software programs for your computer can also perform de-noising. Ultimately what it means is that YOU have more control over how aggressively you de-noise (there's a happy medium between de-noising and loss of detail... so you never want to over-do it.)

The goal is to shoot with the lowest ISO you can "safely" get away with. I say "safely" because given the choice of a blurry hand-held image (because you used too slow of an ISO speed and thus too long of an exposure time) vs. a sharp but noisy image... take the noise. That's because you can fix the noise in post processing... but there's not a lot you can do about the blur unless you're a VERY talented artist. Remember that if the subject isn't moving AND the camera isn't moving then you can use a low ISO and just take a much longer image. You still get a sharp photo AND you don't get the noise (but the tripod needs to be a "solid" tripod so there's no movement or vibration while the shutter is open.)

There's one other element, but it's not very common: The physical temperature of the sensor also contributes to noise. Astrophotographers (who routinely have to take extremely long duration photos... for example a single 45 minute exposure would not be unusual) are plagued by this problem and they use cameras that have special cooling systems in them to combat it.

While a DSLR doesn't have a cooling system... keep in mind that if you use "live view" then you're sensor is active (even though you're not necessarily taking a photo... you're still forcing your sensor to remain active.) That activity causes sensor heat to increase, which in turn increases the "noise".

Sensor heat is usually not a problem on a DSLR because in normal shooting conditions (when you look through the viewfinder) then sensor isn't active. When you take a normal photo, the sensor is only active for a fraction of time -- not enough to build up heat. This means that 99% of the time, it's just high ISO causing the problem. BUT... should you use the video mode or live view mode or happen to take a series of long-duration exposures, just be aware that temperature can become a contributing factor. If at some point this ever becomes an issue... just let the camera rest for a couple of minutes before you resume shooting.