Emitter group> Layer Emitter group

This group lets you emit particles from layers. The Emitter Type Layer must be selected for this group to be active.

The ability to emit particles from 3D layers in the composition is very useful. For example, you can make a logo burst out particles. See our tutorial 'Emitting Particles from Layers' at the middle of this page. Also see our tutorial 'Emitting Particles from Layer Grid' at the bottom of this page.

At left, the full Layer Emitter group. At middle and right, the Layer and Layer Grid options in Emitter Type.

Layer

Selects a layer in the comp that defines a source area for particle emission. Unlike the predefined emitter types, the layer emitter can use the RGB or lightness values from a layer to both define the area where particles will be emitted and drive other particle properties.

Layer Sampling

Defines whether the layer should be read at the particle's birth time only, or continuously updated at each frame. The Current Time option is fine for layers that are composed of text or a graphic that has no animation and the content is the same on every frame. If you want particles to emit based on a layer that has animated content, then choose the Particle Birth Time option.

Layer RGB Usage

The Layer RGB Usage control defines how the particle size, velocity, rotation and color are changed by the RGB values or lightness of the Layer Emitter content.

- Lightness - Size. The particle size is modified by the lightness value at each pixel. Black pixels result in a particle size close to zero, making them nearly invisible, while completely white particles will be created at the particle size specified in the Particle > Particle Size control. Gray values between black and white result in particles size proportionally between 0 and the value in the Particle Size control. For example, a 50% gray lightness value will result in a particle size that is 50% of the particle size value.
- Lightness - Velocity. The particle velocity is affected by the lightness. If lightness is less than 50%, the particle will emit backwards. If lightness is exactly 50%, velocity will be zero. Above 50%, the particles will emit forwards.
- Lightness - Rotation. The particle rotation is affected by the lightness. Lightness values that are less than 50 percent white (127 or less) will have negative rotational momentum. Values greater than 127 will have positive rotational momentum.
- RGB - Size, Vel, Rot. A combination of the preceding menu options, this choice uses the R (Red channel) value to define the particle size, the G (Green channel) value to control velocity, and the B (Blue channel) value to control rotation.
- RGB - Particle Color. This menu choice simply uses the RGB color information at each pixel to determine particle color.
- None. Choose this option to simply set the particle emission area.

Technical issues for layer emitters

- When the Layer Emitter is keyframed and the keyframes are edited extensively, cache inconsistencies can occur. These will manifest as jerkiness in the animation (the Emitter jumps from one frame to the next). To get rid of the erroneous frames from the cache, use Edit>Purge>Image Caches and re-render.
- The layer used as Layer Emitter cannot be a text layer. Instead, create the text in a pre-comp, and use that pre-comp as shown in the tutorial below.
- The layer used as Layer Emitter must have 'Continuous Rasterize' switched off in the Timeline's Layer Switches.

Tutorial: Emitting Particles from Layers

For this project, we are going to make two compositions. Let's start by creating the layer that will be used to emit particles. Start with a new comp (Ctrl/Cmd-N), make it 640x480 pixels at 30 fps, 5 seconds long. Name it 'Boom'.

Type out the letters "Boom!". Use After Effects' stroke and fill color settings to make the word look like this:

Note: An image (or movie clip) could be used instead of the AE text tool. In that case, there is no need to create a separate pre-comp for the image/movie. However, the image should include an alpha channel. Otherwise, if it's on a black background like our text here, black particles will be generated from the black areas.

Now we'll create the main comp. Make a new comp (Ctrl/Cmd-N). Make it 640x480 at 30 fps and 5 seconds long. Name it 'Main'. Create a comp-sized Solid (Ctrl/Cmd-Y), choose Make Comp Size, and click OK. Apply Effect> Trapcode> Particular to the Solid. In Particular, set Emitter> Emitter Type to Layer.
Drag the 'Boom' comp from the Project Window into the Comp Window and let it snap to center. Switch the Boom layer to 3D by check-marking the 3D Layer Switch in the Timeline. Edit the layer's Scale to (50,50,50), then set the layer's X Rotation to 20 and Y Rotation to 320.

The comp should look like this:

Let's start emitting particles from this layer. In Particular, set Emitter> Layer to 'Boom'. Notice that a new light named 'LayerEmit [Boom]' is created. This is a control light that Particular uses to keep track of the layer. It is locked and shy and it's not supposed to be edited.
Set Emitter> Emitter Size Z to 0.
Try a RAM preview to see particles emitted from the text. Notice that all particles are behind the layer. To fix this, move the Boom layer to the bottom of the TLW. Then set in Particular Visibility>Also Obscure with to "Layer Emitter".

Now try a RAM preview again. The comp should look like this:

It's still hard to see exactly what's going on. Let's make it more apparent. In Particular, set Emitter> Direction to Directional. Set Direction Spread to 0. Set Velocity to 200. Set Velocity Random to 0. Finally crank up Particles/sec to 500.

Try a RAM preview again:

Now the particles are generated all over the layer, and the alpha channel of the layer at each particle position is sampled. The transparency value defined by the alpha channel is then assigned to the particle. The RGB color at the position is sampled, and that becomes the particle color.

When Emitter> Layer Sampling is set to Current Time, its default setting, the Emitter layer is resampled for each frame. If the Emitter layer is animated, the particle's colors (and alpha!) will change as they fly. If Layer Sampling is set to Particle Birth Time, then the particle will keep the transparency value and color given at birth throughout its life.

Tutorial: Emitting Particles from a Layer Grid

Now let's have a look at the Layer Grid. Change Emitter> Emitter Type to Layer Grid. Doing so activates both the Grid Emitter and Layer Emitter groups.

Then change the values in the Grid Emitter section to: Particles in X = 20 and Particles in Y = 15.

Now try a RAM preview:

So far we've used Layer Emitter> RGB Usage at RGB - Particle Color. There are other layer emitter options available. To demonstrate the other options, we need a different layer to use as the Layer Emitter.

Create a new 400x400 comp,and name it 'Radial'. Create a 400x400 solid in the comp. Apply Render> Ramp to the solid. Set the Ramp Shape to Radial. Set Start of Ramp to (200,200), set Start Color to white and End Color to black.

The Radial comp should look like this:

Go back to the Main comp. Delete the Boom layer. Drag the Radial comp from the Project Window into the Comp Window and let it snap to center. Switch the Radial layer to 3D and set X Rotation to 20 and Y Rotation to 320.

The comp should look like this:

In Particular, set Layer Emitter> RGB Usage to Lightness - Size. Set Particles/sec to 100. With this option, the particle size is affected by the lightness of the layer.

Hit RAM preview:
Try changing Emitter> Layer RGB Usage to Lightness - Velocity. Now the particle velocity is affected by the lightness. If lightness is less than 50%, the particle will emit backwards as can be seen in the dark areas. If lightness is exactly 50%, velocity will be zero. Above 50%, the particles will emit forwards.

Hit RAM preview: