3.10 Starfields
Once you have generated your favorite fractal image, you can convert it
into a fractal starfield with the 'a' transformation (for 'astronomy'? -
once again, all of the good letters were gone already). Stars are
generated on a pixel-by-pixel basis - the odds that a particular pixel
will coalesce into a star are based (partially) on the color index of
that pixel.
(The following was supplied by Mark Peterson, the starfield author).
If the screen were entirely black and the 'Star Density per Pixel' were
set to 30 then a starfield transformation would create an evenly
distributed starfield with an average of one star for every 30 pixels.
If you're on a 320x200 screen then you have 64000 pixels and would end
up with about 2100 stars. By introducing the variable of 'Clumpiness'
we can create more stars in areas that have higher color values. At
100% Clumpiness a color value of 255 will change the average of finding
a star at that location to 50:50. A lower clumpiness values will lower
the amount of probability weighting. To create a spiral galaxy draw
your favorite spiral fractal (IFS, Julia, or Mandelbrot) and perform a
starfield transformation. For general starfields I'd recommend
transforming a plasma fractal.
Real starfields have many more dim stars than bright ones because very
few stars are close enough to appear bright. To achieve this effect the
program will create a bell curve based on the value of ratio of Dim
stars to bright stars. After calculating the bell curve the curve is
folded in half and the peak used to represent the number of dim stars.
Starfields can only be shown in 256 colors. Fractint will automatically
try to load ALTERN.MAP and abort if the map file cannot be found.