Easy ways to keep the noise down at higher ISO settings
You can use both in-camera and software tools to reduce noise in your high-ISO shots
High ISO noise reduction
You'll usually find this on the Shooting menu, and it's enabled by default on the assumption that people want their high ISO shots to be as smooth as possible. You can switch it off, and it doesn't affect raw files.
Raw noise reduction
If you use Adobe Camera Raw to process your raw files, this is the best time to experiment with noise reduction settings. Bear in mind that reducing noise can reduce sharpness and smooth over fine textures, so you may need to experiment.
Noise reduction in Photoshop
Photoshop's Reduce Noise filter has sophisticated controls for reducing both luminance and colour noise, and with it you can even adjust the red, green and blue channels individually.
Noise reduction plug-ins
Some of the best results come from dedicated plug-ins, like Nik (Google) Dfine 2. These will analyse the noise characteristics in different areas of the image and offer controls for the best mix of detail and smoothness.
Types of noise
There are two different types of noise found in digital images. Luminance noise shows up as a speckled pattern, like specks of black sand, and is similar to the grain that was found when using high-ISO black-and-white films.
Chromatic noise is coloured and looks like the rainbow-like sheen when looking at a patch of oil (and is similar in appearance to the blotchy dye patterns that you saw when enlarging high-ISO colour films).
Colour, or 'chroma' noise is a multicoloured speckling, where neighbouring pixels show random colour variations. This is quite easy for noise reduction processes to remove without harming image detail, and you tend to see it on older cameras.
Luminance noise is caused by random variations in brightness between pixels and it's harder to deal with because noise reduction processes can't readily distinguish noise from real detail. Reducing it will usually have an effect on fine detail too.
You can see examples of both in the infographics below.
[caption id="attachment_538709" align="aligncenter" width="610"]
The crops inset are shown in actual pixels.[/caption]
It's important to look at these two types of noise separately - as each can be reduced using different tools during the editing stage. These are often provided as separate noise-reduction sliders by a raw converter (such as in Adobe Photoshop's Camera Raw utility).
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