Tip of the Week: February 2005 Archives
Not in the film sense (the atmosphere of the bar was gritty and evil), but in the natural sense (the atmosphere in the area looks bad because of pollution).
Even though as compositors we work on a 2D image, we try to convey three dimensions through tricks to fool the eye. Some compositing packages allow for creating the visuals in true 3D, like flame* or Nuke.
A tip to compositing shots that deal with extreme environments is to look at the depth of the image. When you look out across the plains, into the mountains, across the bays, you'll find that as you look farther away, everything becomes smaller, more desaturated, maybe foggier. Depth, atmosphere, and perspective all play a role in creating the scene. These ideals must be carried over when recreating a visual in the computer. Matte painters deal with this all the time; making things look far away by altering the perspective lines, desaturating the picture. As always, reality is your best reference. So get outside and check it out.
You can simulate this reality by adding atmosphere to your scene. Several different methods are available, and it all depends on your timeframe and resources. A very quick way of adding atmosphere is to throw a ramp from black to white on your image, skewed so the white end is further away from you. By desaturating the original image through this black and white ramped mask, you will see that the further away your image is, the less saturated it becomes. Adding a slight haze over this image can be accomplished by mixing in a little blue into the black/white ramp, and layering that over the image again.
You can break this down even further, by using Z-depth renders from your 3D package. If your composite is completely 2D in nature, you can try creating roto to separate the farther reaches of the shot.
The past weeks I've discussed 2D compositing tips and tricks. During the next several weeks I will start going into 3D compositing tips, which you may encounter in your work.
As a general overview, your job as a compositor is to integrate a variety of 2D elements and photographic plates into one seamless composite that appears to be shot at once, in camera. These 2D elements can range from steam and smoke, to large vistas and basic bluescreen and greenscreens. What happens when you're given several different layers of 3D rendered elements? How do you integrate these into a 2D composite? While some packages allow you to build your comp in three dimensions, we still project our finished images on a 2D surface, mainly a film or TV screen.
Your goal here is to visualize the screen in front of you in 3D dimensions. This can be made even harder since your 3D elements are in on a 2D plane! You have to visualize the depth (Z-depth) of the image. Most current image formats comprise of five channels; red, green, blue, alpha, and Z. Depending on the file format, some of them may omit the alpha and Z channels. Pick up a book on image formats to learn more about which channels each file format can hold.
The Z depth channel will hold a grayscale version of the objects in your image. Depending on the encoding, closer objects will be black, while futher objects will be white. In essence, the grayscale image will look like all the objects are in fog.
Some compositing packages allow easier tweaking of the Z channel. Combustion uses 3DS MAX's rpf file format to accurately layer different 3D renders in comp, necessitating only the rerender of one 3D render if something goes wrong. In other packages, we can use the Z depth channel as an alpha, and effectively mask certain areas of the image that we know are behind an object.
It's getting a little late, after a bunch of crazy shenanigans last night (which I'll discuss in a different post). Today I'm going to go into a little bit more detail with a bluescreen key, using our actor, a wonderful cat!
