Answerman
What Is DNR/DVNR, And Why Do People Hate It?

by Justin Sevakis,

James asked:

I have recently been hearing about digital noise reduction (DNR) being applied to reissues and remasters of older media, and some fans complaining about it. However, noise is, by definition, something that is undesired, so should not reducing it be a good thing? Why do some people dislike DNR?

DNR/DVNR, or Digial (Video) Noise Reduction, is a digital filter that's applied to video to remove film grain, video noise (tiny variations in color and brightness that resulted from how video used to be transmitted), film dirt, and other undesirable artifacts from the image. While the technology has been around since the 90s, it has matured a lot; there are many different types of filters that use different methods to achieve the desired results. Most use a combination of two methods: comparing each pixel to its neighbors to figure out if that pixel is a tiny speck that's standing out too much, or comparing the same pixel location in neighboring frames, to see if it disappears.

Why is this important? There are two big reasons. The first is that noise -- be it film grain or analog video noise -- is completely random and changes every frame, making it very difficult to compress cleanly. Once encoded for streaming or for disc, it has a good chance of looking blocky or blurry. Secondly, noise looks far worse on a modern display than it did back when everybody used a tube TV. Old CRTs were very blurry, and whatever noise was part of the signal often couldn't be seen. But modern TVs are so clear that you can see EVERY FLAW.

When used properly, DNR is an indispensable tool for video engineers to clean up messy footage. Video noise, including dot-crawl and rainbowing, can be mitigated and, in some cases, eliminated -- something that makes everyone happy. More controversially, DNR also removes film grain. Film grain is adored by old school movie and anime fans as a reminder of how movies and TV used to look. It's a reminder of the organic nature of film, and to them, is part of the aesthetic. (Different eras, film stocks, and film formats had widely varying amounts of grain to them. 70s 16mm TV series tend to look the grainiest.)

While pretty much nobody appreciates video noise (unless you're specifically going for an 80s VHS look), there is absolutely no consensus in how much film grain is appropriate to leave in. Purists often want to feel like they're getting as close to the original image as possible, and often that means "the more grain, the better!" But mainstream audiences have spent the last 20 years looking at relatively grain-free digital movies, TV shows and home video. To them, it's a layer of distortion, and some people are completely distracted by it. For most modern consumers, a good image is a clear image. And so, with no clear guidance either way, video engineers and the producers that oversee them are pretty much left to go on instinct.

But applying noise reduction is a very delicate, subjective process, and DNR done badly can be truly destructive to the final image. Early DNR hardware was not good at dealing with animation, resulting in fast-moving things like arms, flying objects, or single-frame effects to get partially erased, with multiple frames getting blurred together to cover up what the computer thought was dirt. While that's pretty rare these days, a bad DNR job can leave an image looking overly smooth and blobby, like a plastic toy made for toddlers. Fine details, especially in darker areas, tend to get blurred over.

This is one of those cases where people only notice something when it's done badly, and so the entire process has gotten a bad reputation. When it's done right, some grain is left in, and nobody even notices it happened. But whether you like it or not is immaterial; it's a tool that every video engineer has in their toolkit, and whether or not it gets used (and how well) is entirely up to the skill of that engineer, and the input of the producer they're working for.


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    Justin Sevakis has worked in the anime business for over 20 years. He's the original founder of Anime News Network, and owner of the video production company MediaOCD. You can follow him on Twitter at @worldofcrap.


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