High ISO Noise
Q: Why do my digital pictures get so noisy when I increase the ISO setting on my camera? It becomes unusable at ISO 400 and I hate it.
A: When you increase the ISO setting on your camera you are cranking up your sensor’s sensitivity to light. Unfortunately, you are also making it more susceptible to “noise”, that nasty pixelated graininess that ruins the smooth look of your pictures.
The sensor in your digital camera is made up of individual photosites, each one representing a single pixel in the final image. When photons (light) strike the photosite it causes it to generate a current (electrons) in proportion to the strength of the light it is measuring. These electrons are converted from analog data to a digital image by the Analog to Digital (A/D) converter built into all digital cameras.
You know how when you crank the volume on your stereo you also amplify a background hum or hiss? That’s because you’re also amplifying the background electrical noise present in all electronic devices. When you crank the sensitivity of your camera’s sensor to light, it will also pick up stray electrons that wind up in your image as noise via the A/D converter.
Contamination from neighboring photosites will also add noise to an image. This becomes problematic on cameras with smaller sensors. The more tightly the photosites are packed together, the more the charge can bleed over from one sight to the next, adding noise to the final image.
The general rule is, the larger the image sensor, the lower the noise. A small point and shoot digital camera generally has a 7.2mm x 5.3mm sensor. A mid-range digital single lens reflex (dSRL) has an APS-C (23mm x 15mm) sized sensor. The latter sensor has larger photosites with greater spacing between them. This means it is capable of generating a larger signal to noise ratio and less susceptible to electron bleed from neighboring photosites when running at high sensitivity than the smaller sensor.
If your picture is being destroyed by noise at ISO 400 then you most likely have a camera with a tiny sensor. dSLRs with APS-C sized sensors will generally produce a usable image at ISO 1600. Cameras with a full-frame (36mm x 24mm) sensor – the only ones on the market right now are the higher end dSLRs by Canon, Nikon, and Sony – generate images with spectacularly low noise, and very good looking images even at ISO 6400. Unfortunately, they also come with a spectacular price tag.
Here are some ways you can cope with noise in your digital images:
- Buy a camera with a larger sensor (not cheap, but it works).
- Shoot at lower ISO settings that produce acceptable images. In low light conditions this may require using a tripod or brace to reduce camera movement or adding light by using a flash unit.
- Use noise removal software. There is commercial software on the market that does a decent job of cleaning up noise, but sometimes at the cost of removing fine detail from your images.
Noise removal software generally costs between $50 to $100 dollars and can be a lot cheaper than spending $2000 or more on a new camera. Here are the most popular programs on the market right now:
Sean McCormick
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