Haze Layer
In addition to the clouds, another pass of the Earth is rendered to help with the edges. To simulate the light refracting through the Earth’s atmosphere at the edges, a separate haze pass is rendered (see Figure 38). Because this pass is intended to extend beyond the edges of the original Earth element, it is rendered on a sphere scaled up 5% larger than the original Earth sphere. The smoke texture used for this render is a generic smoke texture and is simply used to break up this particular element.

[Figure 38] (figure is in two parts) Haze render on the top, and blurred haze render outside Earth alpha on the bottom.

[Figure 39] All Earth layers composited together and placed over a star field.

Combining the Earth Layers
Once the elements have been created, the fun of layering them together into a final image begins. The base layer for this composite is the Earth render with the darkened clouds on top of it (see Figure 36). An add operation is used to place the next layer, the clouds (see Figure 37), onto the Earth. This step can be accomplished with either an add operation or an over operation (utilizing the alpha channel created with the luma key). A benefit of the add operation is the control over the precise amount of clouds added to the Earth. For this comp, the clouds were added in at a value of 75%. Another benefit to using the add operation is the mixture of cloud color with the existing color channels of the Earth. Adding a gray cloud RGB value to the green continent backdrop of the Earth results in a cloud with a green tint, as if the cloud were partially transparent. This can also be accomplished with the over function, but an extra step is involved to provide the cloud’s alpha channel for controlling the transparency. After the clouds are added, the final layer in the composite is the haze for the outer edge. This layer offers the same options for layering as the cloud layer, and it too is composited into the image with an add operator. The outer edge is added in at 90% to strongly differentiate it from the background. Once all of the Earth’s layers are combined, they can be placed over a star field to see how it melds with the background (see Figure 39). Notice how the transparency of the outer edge layer affects the stars behind it providing interaction between the Earth element and its surroundings. For the purposes of this book, each layer is a little brighter or saturated to clearly illustrate the points. In the production environment, the art direction might call for such chromatic strength or something more subtle. If the spacecraft is headed for the Earth, and the director wishes the emphasis to be on the destination, then it may well show up in a scene, as depicted here.

Although each of the layers in the Earth composite might seem like elements created independently from each other, it is important to realize the interconnectedness of these pieces. The first step of most composites is to place the basic foreground over the basic background. In this case, the base Earth render would be placed over a simple star field, or possibly even a crude, low resolution image of stars. This first, quick or rough comp (sometimes referred to as a slap comp) is a vital first step in the compositing process. The broad strokes are put down first, and the details can then be added as the shot progresses. In compositing, the first 80 to 90% of the process is usually straightforward. The last 10 to 20% is where the serious amounts of time and energy are necessary for adding the details and fine tuning. Because the first part of the job is easier, it makes sense to look at several rough comps in a sequence before putting the time and energy into the details. The rough edit of these simple comps is valuable in determining whether a shot will work as intended. It’s a much more efficient process if those decisions are made before the painstaking detail work is done. This is true for large film productions as well as small personal productions. The sooner the shots can be cut together, even in the simplest form, the easier it is to get a handle on the need for details, and where time can be saved on things that are unnecessary or will never be seen.