POV-Ray : Documentation : Frequency and Phase
  POV-Ray 3.6 Documentation Online View Transforming Patterns Waveforms Frequency and Phase

The frequency and phase modifiers act as a type of scale and translate modifiers for various blend maps. They only have effect when blend maps are used. Blend maps are color_map, pigment_map, normal_map, slope_map, density_map, and texture_map. This discussion uses a color map as an example but the same principles apply to the other blend map types.

The frequency keyword adjusts the number of times that a color map repeats over one cycle of a pattern. For example gradient covers color map values 0 to 1 over the range from x=0 to x=1. By adding frequency 2.0 the color map repeats twice over that same range. The same effect can be achieved using scale 0.5*x so the frequency keyword is not that useful for patterns like gradient.

However the radial pattern wraps the color map around the +y-axis once. If you wanted two copies of the map (or 3 or 10 or 100) you would have to build a bigger map. Adding frequency 2.0 causes the color map to be used twice per revolution. Try this:

  pigment {
    color_map{[0.5 color Red][0.5 color White]}
    frequency 6

The result is six sets of red and white radial stripes evenly spaced around the object.

The float after frequency can be any value. Values greater than 1.0 causes more than one copy of the map to be used. Values from 0.0 to 1.0 cause a fraction of the map to be used. Negative values reverses the map.

The phase value causes the map entries to be shifted so that the map starts and ends at a different place. In the example above if you render successive frames at phase 0 then phase 0.1, phase 0.2, etc. you could create an animation that rotates the stripes. The same effect can be easily achieved by rotating the radial pigment using rotate y*Angle but there are other uses where phase can be handy.

Sometimes you create a great looking gradient or wood color map but you want the grain slightly adjusted in or out. You could re-order the color map entries but that is a pain. A phase adjustment will shift everything but keep the same scale. Try animating a mandel pigment for a color palette rotation effect.

These values work by applying the following formula

New_Value = fmod ( Old_Value * Frequency + Phase, 1.0 ).

The frequency and phase modifiers have no effect on block patterns checker, brick, and hexagon nor do they effect image_map, bump_map or material_map. They also have no effect in normal statements when used with bumps, dents, quilted or wrinkles because these normal patterns cannot use normal_map or slope_map.

They can be used with normal patterns ripples and waves even though these two patterns cannot use normal_map or slope_map either. When used with ripples or waves, frequency adjusts the space between features and phase can be adjusted from 0.0 to 1.0 to cause the ripples or waves to move relative to their center for animating the features. Transforming Patterns Waveforms

Copyright 2003-2004 Persistence of Vision Raytracer Pty. Ltd.