Minitutorial about polishing cut fractals (en)

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Sometimes we find that, in an already rendered fractal, there is an interference between the fractals and a plane, resulting in a fractal that seems to have been cut (fig. 1). There are at least three ways to avoid this:

Interference by Jakeukalane Fig. 1

  • A. Activating "In and Outside" rendering. This is what I did when I didn't know much about MB3D. It is very slow. Can easily duplicate the time of a fractal because have to render both sides. The description itself of the inside mode is "slow raymarching on the inside with maximum iterations".

Pantallazo del 2016-06-14 14:47:15b by JakeukalaneFig. 2



  • B. Avoiding the "cut surfaces" by walking in or out (remember to tick first, "Fixed zoom and steps"(!), or changing iterations, etc. In resume, using 3D Navi. This is most of the times the better solution.

  • C. We can re-calculate those parts of the image.

And this what I want to explain in this simple tutorial. Sometimes you can't avoid those "cut surfaces" by using 3D navi, or it is unconfortable to do (you already have everything done etc), or even you realize when you see the image rendered (that can happen often when the 3D navi has a very foggy preview).

It is preferible to do this before calculating lights and this kind of things. If not, is preferible to save your m3i before recalculating the image because it changes the lights (I usually mix the images in GIMP, one with good lights, one without cut surfaces). [For further info, see this comment of GraphicLia].

  • 0. We have already rendered the image we want, but there are several "cut surfaces".
  • 1. So, we go to the Formula window and we select  "In and outside" (Fig. 2).
  • 2. We go to the "Post processing window" and we select "Recalculate selection" and "Enable". If we already have calculated lights we press "Don't change AmbSh+dFog" although in my experience sometimes the lights/colours change anyway so that's why doing this before aplying shadows.
Pantallazo del 2016-06-14 15:06:42 by Jakeukalane Fig. 3.

  • 3. Then we go to our image and select the part we want to recalculate and press "Calculate".  Is better to not make enormous selecctions and if we have a point in other part of the image, do the calculation separatedly.

Pantallazo del 2016-06-14 15:09:21 by Jakeukalane Fig. 4

  • 4. After doing two calculations, this is the final image :D
Interference2 by Jakeukalane


This recalculate tool can be used in multiple situations like very grainy images too or artifacts.

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