It’s a problem that happens to even the best of photographers. You take a photo and it looks great on the preview screen. But when you get home and load that photo up again, you get a nasty surprise - your image is covered in tiny little discolored pixels called digital noise. What the heck happened?

Noise is a common issue in digital photography, and it can be a result of a number of factors. Here’s your guide to what it is, why it happens, and what options exist in digital camera noise reduction.

What is noise, anyway?

Simply put, noise is individual spots of discoloration in an image. This is a problem that results directly from the sensor within a digital camera - think of it as the equivalent of film grain for the digital era. Photons strike the digital camera sensor when the shutter is open, generating an electrical signal that the digital camera converts and stores as pixels. The camera depends on a steady stream of photons to produce an accurate image. But in certain situations, various elements affect the camera’s ability to interpret and store information gleaned from the light reaching the sensor, and the result is noise.

What are the main factors causing noise?

1. High ISO/ASA Setting
Just like film came in different speeds, your digital camera has speed settings as well. Higher ISO/ASA settings are a great benefit in low-light conditions, but they have an impact on the noise level on your digital images. A higher ISO/ASA setting tells your digital camera to amplify the signal it is receiving from the image sensor, but it isn’t able to distinguish noise from real image data so the noise is amplified as well. Think of it like this - you have a song with a hiss in it that you can’t really hear when the volume is turned down low. As soon as you crank it up, that hiss becomes more and more noticeable. The same is true with digital camera noise. A higher ISO/ASA setting “cranks up” your digital image, making it brighter but also making the noise more noticeable as well.

ISO/ASA is particularly important in point-and-shoot digital cameras. Oftentimes, consumer-level digital cameras will choose an ISO setting for the photographer as the light conditions dictate. If you are seeing too much noise in the end, see if there’s a way to set the ISO manually. But be careful - lower ISOs come at a trade-off of longer shutter speeds, which can introduce camera shake and blur your images. Sometimes, you’re choosing between two evils.

2. Really long shutter speeds
Your digital camera is an electronic device as well, and its normal operations generate a certain amount of electronic activity. With quick shutter speeds, the other electronic processes going on within your camera don’t generate sufficient interference to be displayed as noise on your digital images. But with longer shutter speeds, the digital camera sensor collects more and more of this background signal. Your camera doesn’t know how to interpret this, so it’s displayed as noise in the resulting image.

3. Image sensor size
Digital camera makers faced a dilemma. People wanted micro-compact digital cameras that they could tuck inside a purse or a wallet, but they didn’t want to sacrifice the eight-megapixels worth of resolution that their buddies with the big, hefty digital SLRs had. Their solution? Just make the camera sensor smaller so it could fit inside a tiny digital camera.

There had to be some price to be paid for this decision, and it came in the cost of increased noise. In a larger digital camera like a DSLR, the camera sensor is bigger. This means that more photons are striking the camera sensor while the shutter is open, giving the camera more data to work with. In a tiny digital camera, the same amount of sensor is crammed into a smaller space. Fewer photons hit the sensor bed, but the camera still has to produce an image that’s the same size as the DLSR. The propensity for sampling errors - misinterpretation of data from the image sensor - becomes greater, resulting in increased noise.

So what can you do about it?

There are several options to help prevent or reduce digital camera noise. The first two are the most obvious and the most effective - use lower ISO/ASA settings or buy a new digital camera with a larger image sensor. But each of these comes at a cost. It requires more light to get a good exposure at a lower ISO/ASA setting, and digital cameras are expensive. In fact, the digital cameras with the lowest levels of digital noise - full-frame behemoths like the Canon 5D - are among the priciest of all digital cameras.

One easy solution is to simply downsize your digital photo. Just like it’s tough to gauge noise levels on a tiny LCD screen, noise is difficult to see in an image that’s been downsized to a smaller resolution.

Another option is noise reduction during post-processing. Setting your camera to RAW mode may offer some relief, as most RAW software packages include a tool to reduce noise within an image. (See Cheapshooter’s article on digital camera settings if you’re unsure what RAW mode is).

Specially-designed software packages also exist that are solely devoted to noise reduction. Many are quite complicated, with options to create a calibration profile for your specific digital camera to ensure the most accurate results.

These software packages can be hit-or-miss, but I’ve always gotten decent results with NeatImage. Noise Ninja is another solution that seems to be popular. With the right settings, these programs do a good job of filtering out noise within your digital images. But be careful - some pictures cannot be salvaged. If you do too much processing with noise-reduction software, you’re libel to end up with an image that looks plasticky and is devoid of any sharpness.

While noise-reduction software can certainly help, noise is just something that needs to be accepted to a degree. Newer generations of image sensors are improving, but expect to find noise no matter what camera you have. It’s something every photographer has to contend with.

Do you have a solution for digital camera noise reduction? Is your camera particularly adept at handling digital noise? Post in the comments and let us know.