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The second resolution parameter, set under the Interpolation Box submenu of the Graphics menu (or the second argument of CRESOLUTION) determines the number of pixels over which color may be interpolated. For FINE resolution, the interpolation scheme starts with a 99 major block of pixels; for COARSE resolution, the size of this block is 1717. Sabrina fires rays at the corners and center of the major block. If these points agree on the surface encountered and the color, the remaining pixels are filled in by interpolation in the intensities of that color; if not, the same game is played on subdivisions of the block. If the image is not too complicated, the COARSE setting may result in faster rendering, but small features may be missed.
The interpolation procedure is unsatisfactory in several situations. A long, thin feature, such as the stirrer in the coffee.sab example, may be inadequately rendered if it passes between the corners and center of the major block. X-ray simulations subdivide on the basis of variation in intensity, which may result in unacceptably jagged X-ray pictures. The SUPER resolution mode, where each logical pixel is ray-traced unconditionally, is available for these situations.