Cellular automata: Transition rules for an image by Juergen Schwietering?

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Offline marcm200

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« on: December 27, 2019, 09:56:50 AM »
I stumbled upon this great image "blue velvet" by Juergen Schwietering back from 2002.

http://www.wack.ch/fame/afc2/pic1/a144b.jpg

(I wasn't sure about uploading someone else's image and copyright, so I'd rather put up the link. Sorry for the inconvenience).

Does anyone know how it was made exactly?

From various sites I gathered that it was based on a software for modelling chemical reactions for crystal growth and probably a cellular automaton, but I couldn't find the transition rules' description.

EDIT Dec 30, 2019: Question tag removed



Linkback: https://fractalforums.org/off-topic/29/cellular-automata-transition-rules-for-an-image-by-juergen-schwietering/3250/
« Last Edit: December 30, 2019, 06:38:45 PM by marcm200, Reason: Question tag removed »

Offline ThunderboltPagoda

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« Reply #1 on: December 28, 2019, 06:54:54 PM »
At his recent website there is a mail link at the bottom. Don't know if it works, but you can give it a try.

Offline marcm200

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« Reply #2 on: December 28, 2019, 09:22:35 PM »
Thanks! That's what I was looking for - and did not find myself (not sure why, "Schwietering" must be my most-often entered search term of last week).

Offline marcm200

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« Reply #3 on: December 30, 2019, 06:40:28 PM »
I sent Juergen Schwietering an email and got a very quick response.

His approach was not based on cellular automata (I was wrong there), it simulated crystal growth by spontaneous crystallization of regions in the plane, extending to some directions, where end points grow further, but were inhibited by other close regions.

My method was not based on chemical reactions: I start with a set of crystallization points, growing in direction of lowest-number-of-crystals in a finite neighbourhood (a ray in that direction). Randomly I chose the horizontal/vertical direction or the diagonal one, randomly extending to the opposite a very short distance.

The image below is an overlay of a time series of some hundred iterations. A pixel indicates in how many time snapshots that pixel harboured a crystal.

I'm quite satisfied with the outcome here. It looks like some underwater corals growing.

Offline scjurgen

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« Reply #4 on: January 22, 2020, 02:10:12 PM »
Hi there

I am the author of these images. I will create a public repo on github for the source code and also post some examples created. Currently stripping the sources down to an understandable version and some modernization as the original source code dates back to 1991 or so.

Cheers,
J├╝rgen Schwietering

Offline scjurgen

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« Reply #5 on: January 22, 2020, 11:49:33 PM »
[...] I will create a public repo on github for the source code and also post some examples created. [...]

Here the repo as promised: https://github.com/scjurgen/lab64

In the repo also two sample images under ./examples and the corresponding ./configs.

Offline marcm200

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« Reply #6 on: January 24, 2020, 01:47:15 PM »
Modifying scjurgen's github project (hardcoding the parameters to avoid external dependency, using a standalone bitmap saving routine) I could compile the code on a Windows-10 platform.

The image resembles the blue-velvet original, although it's not identical, maybe due to the random number generator (different between today's computer and one back in the 90s?) or the use of just 24-bit RGB values - but it gives out a similar vibe.


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