The Advanced Settings dialog box contains calculation controls, that you can adjust for the current fractal.
Note: The default settings in this dialog box are appropriate for casual users of Fractal eXtreme. These controls are available for people either who know what they do or who have mastered the rest of the program and want to experiment with these settings.
To open the Advanced Settings dialog box: On the Options menu, click Advanced Settings.
Going from top to bottom the controls are:
As you zoom further into a fractal, the program requires more digits of accuracy to perform the fractal calculations. The program automatically switches to the appropriate level of precision, based on the zoom level and image size; the Status window's More Info view displays the current level of precision. To ensure that the program is using sufficient precision, you can increase its cushion of extra bits of precision.
Every time the magnification is doubled, an extra bit of precision is required. For example, setting this value to 10 means that the program will switch to the next higher calculation routines ten zooms earlier. If you feel that you are seeing imprecise results, you can increase this setting. However:
For best performance with no quality problems, leave this setting at zero or a fairly low number.
Fractal eXtreme does very aggressive guessing to ensure that it gets the largest possible speed-up (sometimes a ten times speed-up, or more). Then, when it has finished calculating 99% of an image, it does a final pass looking for any pixels that it may have erroneously guessed. This is why the progress bar in the Status window sometimes seems to stop at around 99% for a few seconds. This guess correction finds the overwhelming majority of the misguessed pixels so that the quality of the images is not visibly corrupted, yet enough pixels are guessed that the calculations typically run much faster.
On a few unusual images with very high frequency changes, Fractal eXtreme may initially guess a very high percentage of pixels wrong, making non-existent detail appear. However these errors all get cleaned up at the 99% done point.
For best performance with no visible quality problems, keep this option selected at all times.
Z(n+1) = Z(n) * Z(n) + c
This formula is repeated until either the Maximum Number of Iterations (as set in the Iteration Control window) is reached, or until the absolute value of Z exceeds this specified overflow point (signifying that the calculations will then quickly tend towards infinity).
For the Mandelbrot set, any overflow point from 2.0 or higher will work. The default value of 2.0 is used because calculations are slightly faster and, in many areas, it produces the most interesting images.
You are encouraged to experiment with different numbers. As you increase the overflow point, the bands of colour move slightly out. In some areas this is almost invisible, in others it is very dramatic. Setting the overflow point to less than 2.0 is not mathematically meaningful for the Mandelbrot set, but it still looks cool! The default overflow points for other equations may be different.
On a non-zoomed Mandelbrot, set you can see the effect of changing the overflow point quite clearly, as the outermost bands move outwards.
The Save iteration data control specifies whether to store iteration information in the fractal (.fx) file on disk. By having iteration data available, Fractal eXtreme can remap colours without recalculation, show and hide edges, and render iteration movies, all in real time! Saving iteration data can increase the size of fractal files substantially, so this option is off by default. However, if drive space is not a concern, we encourage you to select this option and make it the default setting so that iteration data is always available.
By default, fractals are calculated at the size as the window in which it is being displayed. You can maximize the main and fractal windows, but you are limited to the size of your desktop. With a virtual screen, you can render fractals at any size, limited only by available memory. The fractal is then scaled down for display to fit its window.
Alternately, you can use the Poster Rendering dialog box to allow you to create even larger images, limited only by disk space - with optional antialiasing.
Note: To save these oversized fractals as bitmaps, use the Save Bitmap Only command in the File menu.
Enabling antialiasing (which can also be done with the Antialiased command in the View menu) does consume additional CPU time and memory. 2x2 antialiasing calculates twice as many pixels vertically and horizontally, thus using four times as much memory, and up to four times as much CPU time. 3x3 antialiasing uses nine times as much memory, and 4x4 uses sixteen times as much memory, so be wary of using high levels of antialiasing, especially on large images. More antialiasing will improve the quality and better remove the jaggies. The actual increase in rendering time is usually less than the increase in the amount of memory, because the guessing algorithm works better on higher resolution fractals.
Antialiasing is particularly useful when rendering zoom movies. If you render zoom movies with antialiasing enabled and then play them back with bilinear filtering then they will look essentially pixel perfect, even when magnified significantly during playback.