Learn more about noise reduction: lightsfilmschool.com/blog/
Video noise reduction and removal tutorial. Learn about noise and ISO settings on your camera.
An ISO setting is the digital equivalent to Film's A.S.A setting. Simply put, your ISO is your camera's sensor sensitivity to light. The higher the ISO speed, meaning the larger the number, the more sensitive your sensor will be to light. The lower the number, the less sensitive your camera's sensor will be to light. Your ISO setting combined with your aperture and shutter speed work together to give you your correct exposure.
However, when shooting in low light environments, better light sensitivity doesn't come without a cost. Let's take a look at this image at night in the park for example. As you increase your chip's sensitivity to light you also increase the amount of "noise" in your image. "noise" is a sort of digital degradation within your image. It manifests itself in different ways in different cameras but it has a general characteristic as a sort of digital grain.
Besides your ISO setting, heat and sensor size also impact the amount of noise in an image. There are also different types of noise. For example, "fixed pattern noise" may be caused by long exposure times. Next, "Random noise", which is seen in this image, is the type of noise most filmmakers struggle with, and is caused by high ISO speeds. Lastly, "banding noise" which plagues some cameras more than others, may be caused when the shadowed parts of the image are lightened.