Shading
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Dialog Box - called from: Input2 Menu

For 8-bit screen display and raster files, the number of shading zones determines the nature of the 256-color palette generated by ATOMS and the number of colors available for shaded atom, bond and polyhedron fills. If the number of zones is 16 or fewer, you can use all 16 colors from the 16-color palette, except black, and there are 16 gradations of each color. If the number of zones is greater than 16, you should use only the first 8 colors in the palette numbered from 0 to 7, each of which has 32 gradations. See Colors, Palettes and Dot Patterns for more details.

Darkness angle (degrees). For an isolated object in a vacuum, the intensity of illumination should vary from maximum to minimum as the angle varies from 0 to 90 degrees. However, this would be a very "hard" illumination, and ATOMS allows for a "softening" or diffusing of the illumination in two alternative ways, by darkness angle or by darkest shade. The darkness angle, or the angle at which the illumination becomes zero or minimal, can vary from 90 to 180 degrees.

Darkest shade (fraction). This option "softens" the shading by allowing the presumed illumination of the darkest zone to be other than zero. Small values of this fraction, such as 0.1 or 0.2, are usually appropriate. It is 0.0 by default.

Use initial pattern numbers. Each atom, bond or polyhedron type is given a fill pattern number or gray shade for use in black-and-white screen displays and dot-matrix images, and this is used if shading is turned off. If shading is on, the shading normally starts from pattern zero, white. However, if the initial-pattern-number option is on, this pattern is used as the initial pattern number, for maximum illumination, other zones then increasing in darkness from this pattern number rather than from zero.

This option can be useful for spherical atoms, which all show the same shading zones, but is less successful for stick bonds and polyhedra, which will show different shading depending on their orientation.

Front-back fading. The initial or unshaded colors of atoms, bonds and polyhedra can be made to darken with depth (decreasing x coordinate). The foremost atom (greatest x coordinate) is considered to have full illumination, and illumination drops off to the rear according to the fading factor. The unit of fading is fraction of full illumination per Angstrom. If the structure has already been calculated, the factor for complete fading (black at the rearmost atom) is shown.