Horizon is a plug-in for After Effects developed by Trapcode and now sold and distributed by Red Giant Software.
In looking at the product website and sample images, I hoped that Horizon was designed to work with Adobe Photoshop’s “Vanishing Point” to enable a high-resolution still image to be cut into pieces and then imported into a composition in After Effects for use as a virtual set, and that the plug-in would maintain perspective between the layers as the camera moved. Unfortunately, this is far beyond Horizon’s abilities. [Editor's Note: For something that is far more similar to what Tom had in mind originally, be sure to check out our January '09 review of Maxon's Studio 4D R11, with its new ProjectionMan Feature.-JH.
Horizon is a single plug-in that performs a very, very specific job. It projects a gradient or an image onto the inside surface of a sphere and then it moves that sphere to match the 3D motion of a camera inside Adobe After Effects. Placing a scene inside of a large textured sphere or hemisphere is a common practice among 3D animators. It can be a useful technique for simulating a believable sky, for creating an environmental backdrop, or just for providing a seamless background image.
Ease of Use
Horizon has an extremely useful flash tutorial online that really shows what Horizon can do and it covers the color gradient capability well. Unfortunately, it doesn’t go into the detail necessary to explain how to use the texture map feature and that part of the plug-in is rather opaque and difficult to understand.
I think you would pretty much have to be an expert in 3D rendering to figure it out on your own and there are dependencies on external programs.
Depth of Options
Horizon’s primary ability is to generate a continuous gradient on the inside of a sphere. Its secondary ability is to project an image layer as a texture map onto the inside of the sphere.
A continuous spherical color gradient that matches camera movement can be quite useful.
A simple color gradient can make a believable background in a 3D composition if there is a compelling object in the foreground that captures attention. Our vision naturally focuses on the plane of interest, where the motion or action is taking place and our vision blurs out everything behind that plane, making it easier to attend to the action. Under these circumstances, the eye forgives a lack of detail or physical correctness in the background, which is the ideal application for Horizon. Red Giant positions Horizon as a companion for use with its other plug-ins that generate foreground animations. For example, in the online tutorial a jet stream is generated using a particle effects system and the background is supplied by Horizon.
Without Horizon, the background animation of even a simple gradient is a lot trickier. You would have to connect a flat background layer to the camera motion by scripting. As you move the camera, you need to be mindful of the edges of the background layer. If the edge of the flat layer becomes revealed, it will destroy the believability of the composition. To overcome this, people often scale the background layer to an enormous size. Depending on how the layer was created, this magnification could reveal pixels or digital artifacts in the background. Another issue with a flat background is that a simple gradient will not have a believable geometry. The gradient changes color linearly, so that at the horizon there is a straight horizontal line. This linearity is a dead-giveaway of a flat background. In reality, the horizon line is curved, and the gradient presents a curved transition between colors, not linear.
Horizon handles all of these issues automatically, making it a lot less work to get a believable 3D composition started.
Horizon uses 32-bit floating point color. So the gradient is smooth and does not show color bands (posterization) as would likely occur if it used 8-bit color.
Horizon allows up to 8 color stops in the gradient. By carefully selecting these colors you can create a very believable featureless sky. The color stops can be used to represent lines approaching the horizon, or they can be used as points, and placed at specific locations to create a more directionless colored surface.