Still images

Particle systems that use still images as their cell sources render in real time much faster than systems that use video or animation clips. A still image is often all you need to create a compelling particle system.

Use the following guidelines when creating graphics for use as particles:

• Graphics size: If you’re not sure what size you want your particles to be, it’s a good idea to make your graphics larger rather than smaller. Increasing the size of particles beyond the size of the original graphic can introduce unwanted artifacts. One caveat, however, is that the larger the cell source size, the slower your playback performance.

• Particle edges: The quality of the edges of your graphics can be extremely important for creating convincing particles. Soft, translucent edges might look better than hard, over-defined ones.

• Object color: By default, particles are created using the original colors of the source image used as the cell. If necessary, you can tint the emitted particles using the Color Mode controls in the Emitter and Particle Cell Inspectors. Choose between tinting all particles with a single color or creating a gradient tint that changes color over time. You can also choose to apply a gradient preset to the particles (see Use the gradient preset pop-up menu). Tinting particles applies the tint color uniformly over the entire particle system.

• Alpha channels: Always create graphics that you want to use as cells with predefined alpha channels. For more information on importing files with alpha channels, see About alpha channels.

QuickTime movies

You can also use QuickTime movies as the image source of a particle cell. For example, you can create an animation in Motion, render it as a QuickTime movie, then import it into another Motion project to use as image source for a cell. In general, the same recommendations for creating still graphics apply to the creation of animation or video clips you intend to use as cells, but there are additional considerations.

Use the following guidelines when creating animations for use as particles:

• Playback performance: Using a movie clip as the image source of a particle cell may impact your project’s playback performance.

• Retimed clips: If you retime a movie clip (in the Properties Inspector or with a Retiming behavior) used as the image source for a particle cell, the effect of the retiming is carried through to the particle system.

• Looping clips: Particles created from QuickTime clips loop over and over for the duration of each particle’s life. If the clip you use doesn’t loop well, there will be a jump cut at every loop point. Another option is to use very short movies to introduce randomness into the appearance of the particle system.

• Minimal compression: Ideally, QuickTime clips to be used as particles should be saved using a high-quality codec, such as Animation, Uncompressed 8- and 10-bit 4:2:2, or ProRes 4444. Other codecs can be used, but they might introduce unwanted artifacts depending on the level of compression used.