Smoothing, smooths the image, so the color transitions are not easily visible. You should use smoothing for Bump Mapping, Fake Distance Estimation, Entropy Coloring and Raibow Palette.
Distance Estimation, sets some points near the boundary of the set to the maximum iterations value. While using this option all the Functions, except Mandelbrot, will be disabled.
While using this option, Initial value, Perturbation, Burning Ship,
and Mandelgrass option will be disabled.
Fake Distance Estimation, emulates the effect of distance estimation without using derivatives.
Entropy Coloring, calculates the entropy of nearby points to create a coloring effect.
Offset Coloring, applies a palette offset to areas with similar iteration gradients.
Rainbow Palette, uses the gradients of the fractal to create a rainbow effect.
Greyscale Coloring, transforms the image to greyscale, in areas with similar iteration gradients.
Bump Mapping, emulates a light source to create a pseudo 3d image, including shadows.