Walker Effects Manual

Channel Noise

Channel Noise applies random noise to layers with individual controls for the red, green, blue and alpha channels. Channel Noise is ideal for visual effects where computer generated elements are composited into live action. And the diverse set of controls make this plug-in a great tool for designers as well. Advanced controls provide infinite scaling, smooth interpolation, and control over the size, density, opacity and blurring of the grain.

Matching Film Grain

A typical problem in visual effects is integrating a computer generated (CG) element with live action footage. Often film footage has noticeable grain that varies in size and intensity, while CG elements have no grain. It is very important to match the texture of the film in the CG elements in order to have a convincing composite.

To begin matching grain you need some sample source footage and the layer that you want to apply the grain to. Start by placing the CG layer so you can see the source footage at the same time. Then apply Channel Noise to the CG layer and begin to work channel by channel to match the grain. It is really helpful if you use the channel switches in the Composition Window (ie the Red, Green, and Blue switches at the bottom) in order to see one channel at a time.

Prerendering Channel Noise

When using the advanced features of Channel Noise, render time can be increased quite a bit. To help save time it is a common practice to pre-render noise. This can be easily accomplished using Channel Noise with the Use Prerendered Noise option. After the noise is rendered separately, the plug-in can then quickly composite the noise onto your layer giving individual opacity and composite mode controls for each channel.

View Mode

The View Mode gives you three rendering options:

Composite

This mode renders the noise applied to the source layer using the Composite Mode specified by each channel.

Noise Only

This mode ignores the input layer and renders the noise over black. This is useful when you want to see the detail of the noise separately from the image, or when you just want to create a noise texture.

Prerender Setup

Use this View Mode to setup Channel Noise to prerender. Prerendering noise is an easy way to cut down on a rendering time, while maintaining some flexibility. After rendering the noise, you can still adjust the Opacity and Composite Mode for each channel.

When setting up the prerender it is important that you turn off all other layers so the comp is just rendering the noise. You then render the comp through the Render Queue saving it to disk. Be sure to output RGB+Alpha. When the rendering is done, import the noise render into the project and bring it into any comp you are using Channel Noise. You can then enable Use Prerendered Noise and select the rendered noise layer.

Tip: You can save more time by rendering a short sequence of noise (like 30 frames) and looping it. You can set footage looping in the Interpret Footage options from the File menu.

Use Prerendered Noise

Use this option to use a prerendered noise layer. By enabling this checkbox, the Prerendered Noise Layer control will become available. Other controls will become disabled in this mode because many settings cannot be changed in noise that is already rendered. The controls that are available are the per-channel Opacity and Composite Mode.

Prerendered Noise Layer

When Use Prerendered Noise is enabled, use this layer parameter to select the prerendered noise layer. For this to work properly, the noise layer should have been rendered using the Prerender Setup View Mode. Once the noise layer is selected, you will be able to control the Opacity and Composite mode of each channel, but other controls will be disabled. For more information on creating prerendered noise, see Prerender Setup.

Noise Type

There are 4 available types of noise. Each type uses a different sampling algorithm that affects the noise texture. Generally, Point noise is the best choice for producing great looking grain at smaller scales. The other options are available for special cases and creating interesting effects. The popup menu lists the choices in order of complexity, and the render time increases with each:

Point

This type produces noise that is rectangular in shape. It is based on nearest-neighbor sampling, however uses interpolation at the edges of the noise pixels for smooth, sub-pixel scaling. For smaller noise, this is the most optimal choice for rendering speed and quality.

Smooth

Unlike Point sampling, Smooth noise uses bilinear interpolation to produce a smoother noise field with no noticeable edges. This mode may be useful when using larger noise scales.

Point Fractal

Based on Point noise, this type iteratively samples the noise to produce varying levels of complexity. With larger scales, the noise takes on a grungy, broken-up look that is more organic than normal Point sampling.

Smooth Fractal

Similar to Point Fractal, this mode iteratively samples Smooth noise to produce a complex, soft fractal noise. This mode is most appropriately used with larger noise scales to produce smooth, but organic looking grain.

Fractal Settings

When either of the fractal noise types is chosen, the Fractal Settings become active. These controls can be used to further customize the grain texture.

Detail

This slider specifies the number of iterations the noise is sampled at. Smaller values result in faster render times, but coarser grain. Larger values produce a very nice looking fractal but take longer to render.

Offset

The Offset value determines the positional difference between each fractal iteration (set by the Detail). Lower values of Offset can create duplicate overlapping patterns in the noise, acting almost like a focusing effect, while larger values create more randomness.

Frequency

This value sets the difference in scale between fractal iterations. Each iteration is scaled by the Frequency to create increasing or decreasing sized grain. This feature is helpful for controlling whether noise tends to get larger or smaller with increasing Detail.

Quality

The different Noise Types are each affected by the quality of the rendering. At Best Quality the sampling algorithm uses sub-pixel sampling and can dramatically affect render time. To give the user more control the noise quality can be specified independently, or in relation to the layer.

Layer Quality

This is the default mode for noise quality. In this mode, Channel Noise will match whatever quality the layer is rendered at. Note: Layer quality is set in the Timeline Window by toggling the / or \ in the switches section.

Draft Quality

Setting Draft Quality will force Channel Noise to render faster by foregoing sub-pixel sampling. This can save a lot of render time, but may also produce courser results. Generally, draft quality looks fine when the noise is not being scaled or moved over time.

Best Quality

With this mode enabled, Channel Noise will always use sub-pixel sampling to produce the smoothest, cleanest noise. This mode is best used when you need to ensure that small scale values are being render nicely, or when noise is being animated in size or position over time.

Color

The color control relates directly to the amount of noise in each channel. It is helpful as a quick way to set the noise amounts, or to use the eyedropper to approximate a noise color. Note that the resulting noise color is affected by the Composite Modes used by each channel and how it mixes with the input layer.

Channel Group

Since each set of channel controls are identical to each other, they will be covered generally here. To help optimize rendering, each channel of noise is only rendered when the Opacity is greater than 0. When a Channel group is not being rendered, it becomes disabled (gray) and the sub-controls will become inactive.

Opacity

This controls how much noise is applied in each channel. Opacity simply fades the noise off and on, from 0 to 100%. If Opacity is set to 0, the Channel group effectively becomes disabled and render time is reduced. The Opacity is directly linked with the Color control and a change to one will affect the other.

Density

Unlike Opacity, Density actually affects the amount of noise. The default value of 1.0 results in perfectly uniform noise. As Density decreases towards zero, the noise grains will become more and more sparse, until there is nothing left. And as Density increases towards 2.0, the noise becomes more and more dense until it is solid.

Size

One of the very useful features in Channel Noise is the ability to set the grain size per channel. Size affects the apparent scale of noise. Greater values will produce noise that is visually larger, while lesser values will produce smaller sub-pixel grain. The Size controls can be set uniformly or independently. To get the best looking grain at any size, set the Quality to Best Quality.

Note: Very small grain sizes can have a big impact on render time due to the amount of sampling required. An alternative to making grain very small is to lower the Opacity.

Uniform Size

When this checkbox is enabled, only a single Size slider will be provided. The value set by this slider affects both horizontal and vertical dimensions of the noise. If Uniform Size is not checked, then two sliders will become active: Size X and SizeY. When toggling Uniform Size on and off, the Size X value is the same as the Uniform Size value.

Blur

Blur can be used on each noise channel to soften the grain. The blur size is measured in pixels. Keep in mind that larger blurs take longer to render.

Uniform Blur

With this checkbox turned on, the Blur slider value affects both horizontal and vertical blur. When Uniform Blur is not checked, individual controls are given to blur the horizontal and vertical dimensions independently.

Composite Mode

How the noise interacts with the source footage is determined by the Composite Mode set for each channel. These modes work the same as the built-in After Effects Composite Modes, plus additional modes proprietary to Walker Effects. This flexibility is invaluable for accurately matching film grains and controlling how the noise affects the source, whether brightening, darkening, or both.

Randomize Each Frame

When enabled this checkbox will cause Channel Noise to render a unique noise pattern for each frame rendered. It does this by adding the current frame time to the Random Seed. If this is left unchecked, then the noise pattern will be the same on each frame and therefore does not animate.

Random Seed

To add further control over how random each frame of noise is, you can set the Random Seed explicitly with this slider. This may be desired if an effect is copied to another layer and needs a unique noise pattern.

Position

By setting the Position, you define the center of the noise. This affects the center from/to which noise scales. When animating the Position, for best results set the Quality to Best Quality.

Opacity

This value is multiplied with the Opacity value of each Channel group and acts as a master Opacity control. At a value of 0, Channel Noise will effectively render no noise and simply pass through the source layer. If the View Mode is set to Noise Only, this slider becomes inactive.