6:1 compression, at the expense of reduced colour fidelity. The second stage performs run length encoding on the 32-bit pixel values. This has a limited impact on the size of most rendered images, but it is fast and simple. Scene description format A radiance scene is made from one or more object files. The .rad format is a simple text file. It can specify individual geometric objects, as well as call programs by starting a line with an exclamation point '!'. When specifying geometry the first line is modifier type name The following three lines contain parameters starting with an integer specifying the number of parameters. The parameters need not be on the same line, they can be continued on multiple lines to aid in readability. Modifiers create materials and can be chained together, one modifying the next. For example:myball.rad chrome sphere ball 0 0 4 0 0 10 10 This can then be arrayed in another file using the xform program (described later):scene.rad void metal chrome 0 0 5 0.8 0.8 0.8 0.9 0.0 !xform -a 5 -t 20 0 0 myball.rad This creates a chrome material and five chrome spheres spaced 20 units apart along the X-axis. Before a scene can be used, it must be compiled into an octree file ('.oct') using the oconv tool. Most of the rendering tools (see below) use an octree file as input. Tools The Radiance suite includes over 50 tools. They were designed for use on Unix and Unix-like systems. Many of the tools act as filters, taking input on standard input and sending the processed result to standard output. These can be used on the Unix command line and piped to a new file, or included in Radiance scene files ('.rad') themselves, as shown above. Geometry manipulation Several radiance programs manipulate Radiance scene data by reading from either a specified file or their standard input, and writing to standard output. xform allows an arbitrary number of transformations to be performed on a '.rad' file. The transformations include translation, rotation (around any of the three axes), and scaling. It also can perform multi-dimensional arraying. replmarks replaces certain triangles in a scene with objects from another file. Used for simplifying a scene when modelling in a 3D modeller. Generators Generators simplify the task of modelling a scene, they create certain types of geometry from supplied parameters. genbox creates a box. genrprism extrudes