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Ray Tracing Resolution
A logical pixel is that portion of the viewplane whose color is determined by a single ray. The time required to compute an image is proportional to the number of logical pixels that need to be defined. The number of logical pixels used in an image depends on the number of screen pixels in a ray tracing window and a resolution factor. The resolution settings are specified on the Ray Tracing Resolution property page. The choices in the Pixel Size box specify the number of screen pixels per logical pixel. A single ray trace determines the color of a 4x4 or 2x2 screen pixel block or a single screen pixel.
The Interpolation parameter determines the number of pixels over which the color may be interpolated. For FINE resolution, the interpolation scheme starts with a 9x9 major block of pixels; for COARSE resolution, the size of this block is 17x17. Rays are computed 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. In an etch picture where cell and/or lattice boundaries are shown, the points must agree on cell number and/or lattice element to avoid subdivision. When shadows are present, interpolation is between points that are all in or not in shadow. Interpolation is never done using points showing a semitransparent cell; each pixel of a semitransparent region is always calculated.
A 17x17 block and its subdivisions
If the image is not too complicated, the COARSE setting may result in faster rendering, but small features may be missed, as shown above.
In the SUPER resolution mode, each logical pixel is ray-traced without any interpolation.
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