Thomas de Groot <tho### [at] degrootorg> wrote:
> Op 11/04/2021 om 14:48 schreef Mr:
> > The polished one however really shows the repetition of procedural texturing too
> > visibly, to the point that it breaks everything else, which would otherwise of
> > course work fine for a polished material...
>
> I have a nagging question: Is the granite pattern a /repetitive/ pattern?
>
> Because I do not understand your comment about procedural texturing
> here. In addition, I checked the result against a Real World example and
> they are close. You will read in the header of granites21.inc that these
> granites are based on Real World examples by the original author, and so
> they are.
>
> --
> Thomas

Since I'm invited to develop, I will, but please bear with some convoluted
stream of gut feeling rather than thought process:

Is the pattern really mathematically repetitive? What matters more is, does it
just even vaguely look like it is?

One of the key to overcome the "repetitive look" could be to break the scale
invariance. what I call scale invariance would be a strong inherent component of
computer generated fractal imagery: what is bigger looks quite like what is
smaller. so we add a depth pass to refine detail adding say one voronoi cell
inside another voronoi cell now it has depth of 2. this may look fascinating as
it reminds the way nature does (a tree has branches over branches). It is even
more so (fascinating) thanks to the computers ability to randomize that cell big
or small, say with a rotation or whatever (e.g. tree's species branching could
be described as generally between this and that angle for generation of branches
out of trunk and these other angles for generation 2 of branches out of branches
1) so let's have the computer pick randomly a rotation value between these max
and min and even state that it should never pick twice exactly the same
number... sounds good,

BUT

Nature has kind of two margins for this randomness... The one that makes one
recognize the represented object's characteristics, here they are perfect.
AND the one that is over these boundaries but still occurs from times to times.
The important thing is to really allow the additional level of detail (big or
small) to go there, but still control this probability to a small amount and not
have it constantly embedded in occurring variations, even if it's
programmatically made to mathematically never be that exact one. Or else, a) it
would look like repetition and b)more importantly,  it would break resemblance
to the represented object, since we're not talking of the characteristic
frequent values but rather the extremes.

What the **** am I talking about HERE ? :-)

For this granite, here is a CC0 image that could come out as a pretty standard
search result, rather consistent across the four or five first results:

https://en.wikipedia.org/wiki/Granite#/media/File:Fj%C3%A6regranitt3.JPG

If this was taken from say 1m away from surface with a 50/80mm focal length. And
we tried to roughly approach the pov scene to cover the same field of view.
Then if both in the photograph and rendered image one circled the salmon colored
areas. One difference I would expect in resulting circle clouds to weight for my
point in the balance: the radius would be almost constant in the pov result
while the photograph shows isolated much bigger circles sometimes occurring. My
gut feeling was just that the lack of these extreme occurrences gives the image
the look of a fractal image from the nineties. Now that was a nice period, and I
do value data preservation and archeology, I only fear the newer looking results
are currently just not included along at all with POV package despite its being
perfectly capable of it, as great images in these newsgroups frequently prove.
I fear people tend to shy away from pov these days because of somewhat hidden
modernity.

Maybe the first image looks much more natural to me because the additional black
dimples and accurate roughness provide enough additional detail and variation
especially at a lower frequency concerning the roughness because its shading is
graded over all of the object.

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