Video noise usually looks like a slight snowyness on video, and it can also look like little flickering blue and green and red and colored pixels. How to remove them?
Video noise can easily be removed by a simple plugin called Neatvideo. It works with most all popular video editing software.
What causes video noise? For a more technical explanation:
The camera has a sensor in it that is basically a grid of little tiny photoreceptors. Every photon of light that hits a photoreceptor is absorbed and increases the electric charge in that photoreceptor. After the exposure time is up, all of the charges in each photoreceptor are dumped into circuitry that measures how much charge was in each cell. The greater the charge, the brighter the pixel.
Note that these photoreceptors only measure brightness and not color, so to get color you either have to place an alternating grid of filters over the sensor, or you have three sensors (one each for red, green, and blue) and a prism that splits light out to all three.
Noise comes from two causes, but the primary cause is photons aren't the only thing that can increase the charge held in each photoreceptor cell. Heat can randomly increase the amount of charge by just a tiny little bit. In direct sunlight this isn't too much of a problem since there are a lot of photos hitting the sensor and they tend to overwhelm the noise.
Low-light is where the noise becomes apparent when there are fewer photons hitting the sensor so the charge amounts are run through an amplifier (so the generated image will be of the proper brightness) which also amplifies the effect of the random charge noise introduced by heat. The greater the amplification of the charge signal from the sensor, the greater the noise. This is why the more sensitive ISO settings on a DSLR camera are grainy. It's the same effect.
The other thing that causes video noise is the photons themselves. Photons bounce around willy-nilly so the number of photons will vary slightly between photoreceptors and between frames for the same photoreceptor. This accounts for some of the low-level noise you see in a daylight video shot. Once again, in low light the amplification applied to the signal from the sensor will also amplify the slight photon variations into larger variations.
The same thing happens in video filters. If you have an image or video with a little grain and increase the brightness or contrast it will amplify all the little variations and result in more visible noise. The reverse is also true: reducing brightness or contrast will lessen the noise. If you can overexpose your video (without blowing out your highlights) and then darken the exposure in post, that will reduce some of the visible noise. Note that this only works if you increase your exposure by altering your aperature or shutter speed. If your video camera brightens the exposure by simply amplifying the sensor signal (this is how cheaper cameras do it) then you'll gain nothing since the overexposure will introduce more noise from the start.
That then covers the technical explanation behind video noise. Now, how do we fix it?
It is here that I was introduced to a software program called Neatvideo. I can definitely recommend it for any video noise reduction.
Granted, their website looks like something that was designed in 1997. However, this is one instance in which substance is better than dressing - the software works marvelously!
In Premiere Pro for example, you put Neatvideo as a filter on top of your video clip, click on the filter settings, let it auto-select a "profile" from the video picture, and click OK, unless you'd like to play around with more settings. Remember that there are also settings inside the "Effects Control" of the clip, so you can tweak it further. With use, you'll see what every Neatvideo setting does.
Look at especially the sky in this frame grab example, how it is smoothened out beautifully with Neatvideo:
I have since getting myself Neatvideo, also used it to fix a whole variety of video noise types, from VHS transfers to low light conditions to smoothing brightened video, to doing better composites.
Neatvideo works astonishingly easy! You can purchase a plugin for your video editing application, in my case Adobe Premiere CS3 (nowadays CS5), and, once installed in the right folder (the installation didn't place it in the right folder on my system, so I had to see to it that it is in the right folder myself) NeatVideo can be selected under your normal Video Effects.
Once the Neatvideo Noise Reduction effect has been placed on a video clip, you simply click the setup button for it and there you can click to have an automatic "device profile" created. Slide the amount of noise reduction sliders and the sharpness, and viola! You're done.
It seriously has helped a lot on a lot of my shots that were filmed in low light. You know that snowy grainyness you get in the darker low light parts of your video? Neatvideo smoothens that out beautifully.
I also have some really old footage on VHS of a short film I made years ago, which has a lot of grainyness on it. I'm certain that Neatvideo will clean it right up and make it look like beautiful digital video.
Thanks to Neatvideo for a fantastic video denoiser!