randy b

I was reading about this chaotic map on wiki --

http://en.wikipedia.org/wiki/Arnold%27s_cat_map

I want to use this algorithm in Jitter to manipulate images...

I don't really know where to begin and would appreciate any advice...

Hey, 
I was reading about this chaotic map on wiki --
http://en.wikipedia.org/wiki/Arnold%27s_cat_map   

I want to use this algorithm in Jitter to manipulate images...
I don't really know where to begin and would appreciate any advice... 

arnolds-cat-chatic-map-2

Take a look at jit.repos. For mapping functions, I usually find it easier to use jit.repos with the @mode 1 attribute (relative repositioning instead of absolute).

There is something that has confused me about jit.repos: for a given pixel, it determines where that pixel is coming *from*. These math formulas tell you where a pixel is going *to*. So you normally need to calculate the inverse transformation for use that with jit.repos, but actually I don't think it will matter for this particular transformation. Just something to be aware of in the future.

Hi Randy,
Take a look at jit.repos. For mapping functions, I usually find it easier to use jit.repos with the @mode 1 attribute (relative repositioning instead of absolute). 

There is something that has confused me about jit.repos: for a given pixel, it determines where that pixel is coming *from*. These math formulas tell you where a pixel is going *to*. So you normally need to calculate the inverse transformation for use that with jit.repos, but actually I don't think it will matter for this particular transformation. Just something to be aware of in the future.


Forgot to mention: you will want to look at jit.expr for how to build the transformation matrix for jit.repos. It can be very confusing at first, took me a while to figure out. I can try to get an example together later if you are stuck, so let me know how it goes.

This example is more complicated because it uses imaginary numbers in the transformation, but maybe it will give you some hints: 

https://cycling74.com/forums/index.php?t=msg&goto=125303

This example is more complicated because it uses imaginary numbers in the transformation, but maybe it will give you some hints: https://cycling74.com/forums/index.php?t=msg&goto=125303


I had some time to play with this last night.

I find it helpful to use patches like this to figure out how to make a jit.repos transformation matrix:

From that and a bit of experimentation I got a working "cat map" patch. I noticed the image dimensions affect how many iterations it takes to end up where you started. If you want to change the dimensions, you need to change the jit.qt.movie on the left and the jit.matrix on the right. They need to be the same and should be a square. Rectangular dimensions seems to dissolve permanently into noise.

I had some time to play with this last night. 

From that and a bit of experimentation I got a working "cat map" patch. I noticed the image dimensions affect how many iterations it takes to end up where you started. If you want to change the dimensions, you need to change the jit.qt.movie on the left and the jit.matrix on the right. They need to be the same and should be a square. Rectangular dimensions seems to dissolve permanently into noise. 

Arnold's cat Chatic map