How to prevent and correct digital noise
Noise in digital files is due to physical limitations on the camera, primarily the sensor itself, but partially the rest of the processing system. It can be minimized by the choice of camera, ISO setting, camera settings, and for Raw files, how they are converted.
How do I prevent noise in my images?
All else being equal, a larger sensor will have less noise. Small sensor point-and-shoot cameras will have more noise than the larger dSLR sensors, and those cameras will have more than the medium format backs. That’s assuming the same pixel count, ISO setting, and technology are used.
All else being equal, newer technology will have less noise. A new sensor design will have less noise than an older one of the same size and pixel count.
And, a properly exposed image at a lower ISO setting will have less noise than one using a higher ISO setting. Use the lowest ISO setting available to get the capture.
Underexposure increases noise. In almost every camera, a properly exposed image at ISO 400 will have less noise than one that’s underexposed 1 stop at ISO 200.
Sharpening increases noise unless you sharpen using a tool that masks minor variations. Photoshop’s Unsharp Mask filter permits this via the Threshold setting; a higher setting exaggerates noise less. Some other new sharpening tools also provide this option. Most older or basic ones do not.
How do I correct noise in images I’ve already taken?
Depending on the noise, much of it can be dealt with in Photoshop. There are some excellent tutorials on noise-reduction techniques available.
Here are some to start with:
- Sean Duggan’s excellent article from Layers Magazine (It covers many approaches and discusses some Camera Raw settings to reduce noise as well.)
- Sue Chastain’s overview of the Reduce Noise filter
- Mike Rodriguez’s video using Photoshop’s built-in Reduce Noise filter
- Mikkel Aaland’s descriptions of noise reduction techniques
Many other advanced techniques are also available; a web search should find many options.
Aren’t there tools that do this automatically?
Yes. Most provide only minor improvements or advances over doing the work manually, but most can drastically reduce the amount of time and effort required.