De-noise and de-artifact

This is an excerpt from a book I'm working on called Greensreening & Keying for Low-Budget Indie Filmmakers that will be out next spring. This has not been through the editor yet, so consider it a super early sneak peek! I had actually started this article a couple of months ago for Toolfarm and thought it would be great to put in the book. The book is about keying, obviously, so the article below is geared toward that glorious task. Reducing grain is something that can be used with any footage though, even if you're not keying. I know you knew that already.

------

You will get much cleaner keys if you first reduce artifacting, noise and grain in your footage. This step may not be necessary if you have awesome footage, but if you're shooting DV, a quick clean up will help your key and your video look immeasurably cleaner.

Noise can come from bad lighting, JPEG and other compression induced artifacting, film grain, and half-tone patterns. In DV footage, blue will almost always be the noisiest channel and green is the cleanest channel.



There are several methods of reducing noise. A median filter set to a very low value will often do the trick. After Effects ships with a very nice Remove Grain filter, which I highly recommend using. It will soften your footage if you use it to high but in small doses, it can do wonders.

Angie Mistretta, visual effects artist and Apple Shake user, has this advice, which applies to pretty much any host application. "Be sure to degrain your footage via each channel." Sometimes a soft blur on the blue channel will do the trick, but do so very carefully. Most of the time, that won't be enough.

Angie adds, "If you need to Shift Channels, degrain each one and then reunite the channels then that is what you would do. Shake has a node that will allow you to tune for each individual channel."

In After Effects, to degrain per channel, try the Remove Grain plug-in, which ships with After Effects. Apply Effect > Noise & Grain > Remove Grain. Remove Grain does a great job of figuring out the algorithm behind the noise and getting rid of it.

Remove Grain and several third party plug-ins have a Preview Region, which is a white box that shows you a preview of the plug-in. Inside the box, you'll see the effect working and outside the box is just the regular footage. This helps speed up render and screen redraw time. By clicking and dragging the center point of the preview region, you can drag it to the area that you want to use as reference.

Under the Noise Reduction Settings > Mode, you can specify whether you want to reduce noise in all channels (multichannel) or in one channel at a time (single channel). Because noise in video is mainly in the blue channel, the noise reduction can be set higher than the other channels.

When reducing noise is useful to see both the combined RGB and a single channel, so you don't have to switch back and forth between channels. This feature is useful for a number of other purposes too.



To open a second comp viewer:

1. At the top of your comp viewer, click on the title of your composition. A pulldown menu will appear. Select 'New Comp Viewer'.
2. Drag the new composition tab to the right side of the comp viewer window, until it highlights purple and let go.
3. To change the channel being viewed for the new comp viewer, use Show Channel at the bottom of the comp window.

Remove Grain doesn't work well with dirt or dust on video, because it works with the full frame of video. You can adjust the Sampling points under the sampling menu. The sample points should be placed in an area of mid-tonal ranges and with no natural texture, such as over trees, water or a stucco wall. It will calculate the noise based on the texture and will not help your cause. Mark Christiansen's book, After Effects CS3 Professional Studio Techniques, talks about the Remove Grain plug-in used to give an aging actress a tighter face, so occasionally using this plug-in for a digital Botox on a skin texture can be very useful! By default, the sampling points are taken from the first frame. You can adjust and keyframe the source frame also.

You will also want to adjust the Noise Reduction Settings and the Fine Tuning in Remove Grain. Be careful not to be too heavy handed with the effect because it will flatten your textures. Before rendering, switch the Viewing Mode to Final Output.



When you're removing noise specifically for keying, many keyers have built-in noise suppression. The Foundry Keylight has a Screen Pre-blur and Screen Softness Options.

Sometimes Remove Grain just isn't enough and you need a third party solution for reducing noise. Check out Reduce Noise, Grain and Artifacting in our Plug-in Finder for a long list of plug-ins for several host applications. There really are a lot of great choices. Here are a couple that I use.

• RE:Vision Effects DE:Noise - Peter Litwinowicz, Co-Founder of RE:Vision Effects said, "Noise in the green screen areas can hamper your ability to pull a great key. DE:Noise is a great plug-in to help pull a better key, because it helps eliminates noise while keeping sharp the details and edges of your objects of interest." De:Noise works with After Effects, Premiere Pro, Boris Red, Combustion, Final Cut Pro, Motion and Fusion.
Digital Film Tools Composite Suite - Deartifact is handy for cleaning up artifacts caused by DV and HD video footage. In fact, it is useful for cleaning up images that have aliased or jaggy edges.
• Boris FX, Inc. Continuum Complete has two noise removal filters, BCC DeGrain Filter and DeNoise Filter. BCC DeGrain removes grain-sized noise from an image by analyzing a sample of the grain, then filtering out image noise that has similar frequency (spectrum) and amplitude. The BCC DeNoise filter removes unwanted pixel noise from an image. DeNoise is especially useful when working with archival materials, as it lets you correct dark areas that show artifacts from film emulsion or video compression. You may also want to use the BCC DeNoise filter when resizing 4:3 images to 16:9 aspect ratio. BCC is available for pretty much every host app you might use.


• Red Giant Software Key Correct Pro is made specifically for keying and quickly clean up noisy images and mattes. Use the simple Denoiser and Alpha Cleaner tools to fix low-light noise problems in poorly lit footage

Labels: DE:Noise, Keylight, Plug-in Finder, Re:Vision Effects, The Foundry