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fir

fractal result by accident

42 posts in this topic

I was tinkering a bit with my basic raytracing code and by accident i

received some kind of fractal pattern

 

 [attachment=19801:ff.jpg]

 

does maybe someone know if it has some official name? i think i saw this already in some book or something

 

the code to get this is like i was counting distance from screen points (along the rays) to sphere (this distance should be about 0 to 1000)  then just multiplying this by 255.9

casting to unsigned and adding it like

 
  unsigned color_ = (red<<16) + (green<<8) + (blue);
 
then setting pixel :/ i do not know exactly reason of this outcome but it is funny ;\ (in mathematical way)
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Looks like normal sampling aliasing or interference patterns. As the frequency of the rings increase, they approach and pass the limit at which you sample the rings at the pixels.

may be but besides is a some specyfic fractal structure, (type of fractal) probably/maybe has some name

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Zoom in on those structures and see what happens when you get closer to them. If the patterns change as you zoom in, then this is definitely just normal sampling aliasing. The fact that you only calculate a distance and transforms it into some color means that the pattern should just be circular rings around a center point, but circular patterns with too high frequency for the display produces those particular patterns. Nothing fractal at all about it.

 

I cannot agree this is not a fractal, iMO this is a well defined fractal.

 

I think this coloring is stable, it is you probably can paint a real wooden

ball this way - this is probably effect of colouring some geometrical surface based on distance to point with cyclic palette - you will get stripes here, if distance would be counted from only one point you will

probbly get centric circles on a ball, but this distance is counted not

from one point but from each screen pixel so it results in such strange fractal (this is what i think i am not sure)

 

zooming the ball I think will not change the effects with covering spray

(just zooming it) but probably with rising the spatial frequenzy of palette wil uncover infinite complexity of the rings... that i suspect

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Clearly an aliasing effect and nothing fractal about it.

 

If you say so ;\ (yawn)

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It does: Moiré

Aye. This.

 

You could see those on TV a lot in the 1970/1980s when TV technology was low-res, low definition interlace stuff, TVs were sucky CRTs, and news anchors would wear checkerboard jackets.

 

Early scanners (when 120 DPI was considered high quality and you had to pull the scanner over the original by hand) had a lot of that too when you used to scan printed media. Nowadays, scanners seem to have some smart kind of supersampling/antialiasing technology built-in.

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Clearly an aliasing effect and nothing fractal about it.

 

If you say so ;\ (yawn)

 

 

Why do you bother asking if you're just going to reject the answers you get if they don't match your predetermined presumptions? I concur that it just looks like a Moiré pattern.

Edited by Ameise
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I cannot agree this is not a fractal, iMO this is a well defined fractal.

 

These things have definitions. Start by specifying precisely what set you are talking about, then compute its fractal dimension. If the result is not an integer, you do have a fractal.

 

 

i dont know how to count a dimension do you know how to count this based on that picture?

Edited by fir
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...probably/maybe has some name.

 
It does: Moiré

 

this is not this thing, as i said the thing is a result of normal colorizing the surface with a stable preducted palette, no 'border' artifacts or interferency things

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...probably/maybe has some name.

 
It does: Moiré

 

this is not this thing, as i said the thing is a result of normal colorizing the surface with a stable preducted palette, no 'border' artifacts or interferency things

 

As befits an encyclopedia, the linked Wikipedia article takes a narrow and precise view of what a Moiré pattern is, However, it's common to refer to most interference patterns as Moiré patterns, because they are essentially similar patterns regardless of the type of interference.

And aliasing is an interference pattern, between the sampling points and the features of the continuous signal.

In this case you are sampling (at pixel location) a wildly wobbling and discontinuous signal: the quantization error obtained by converting the eye-sphere distances to integers.

 

 

This is not interference involved also not precision errors or something, this is just a stable way of colorisation of the sphere also i think it has an infinite indepth complexity here (if you wil rize up the palette frequenzy to infinite, as i said, ), here is some 'zoomed' example yet

 

[attachment=19816:some.jpg]

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This is not interference involved also not precision errors or something, this is just a stable way of colorisation of the sphere also i think it has an infinite indepth complexity here (if you wil rize up the palette frequenzy to infinite, as i said, ), here is some 'zoomed' example yet

 The circles form one pattern, and the pixels forming the discrete sampling grid is the second pattern. The interference is implicit from the intersection between the two patterns when you sample the continuous circle pattern at the discrete pixel grid.
 

attachicon.gifsome.jpg

Overlay that image and the one from your first post and you'll see that the interference patterns, or fractals if you want, are not the same; neither at the equivalent scaled location or at the equivalent scaled size. Your patterns are thus resolution dependent. That's precisely how interference works.

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This is not interference involved also not precision errors or something, this is just a stable way of colorisation of the sphere also i think it has an infinite indepth complexity here (if you wil rize up the palette frequenzy to infinite, as i said, ), here is some 'zoomed' example yet

 The circles form one pattern, and the pixels forming the discrete sampling grid is the second pattern. The interference is implicit from the intersection between the two patterns when you sample the continuous circle pattern at the discrete pixel grid.
 

attachicon.gifsome.jpg

Overlay that image and the one from your first post and you'll see that the interference patterns, or fractals if you want, are not the same; neither at the equivalent scaled location or at the equivalent scaled size. Your patterns are thus resolution dependent. That's precisely how interference works.

 

 

I changed the palette frequenzy up 5times (by putting the ball more far now its centre is 5 km far and has a radius of 3.5 km)  in the second picture as i said more details is wisible when rising up the palette frequenzy - what is interfering with what? (I do not see a need of talking 

about this interferentions here, i do not see them, it would be better to talk about math structure of this pattern, but i m not to much educated in hyperbolic geometry or such things)

 

ps probably i could rise up the visual effect by defining nicer palette 

(but not sure if got a time to do this today)

Edited by fir
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what is interfering with what?

It has been said many times already; the circular pattern is interfering with the pixel sampling grid. At the center of the ball, the frequency of the circular patterns are low and do not alias when you sample it at the discrete pixel locations. At the higher frequencies, the circular patterns do alias becuase you cannot capture the high frequency details with the low sampling frequency. That is where the interference patterns are coming from.

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what is interfering with what?

It has been said many times already; the circular pattern is interfering with the pixel sampling grid. At the center of the ball, the frequency of the circular patterns are low and do not alias when you sample it at the discrete pixel locations. At the higher frequencies, the circular patterns do alias becuase you cannot capture the high frequency details with the low sampling frequency. That is where the interference patterns are coming from.

 

this is not dependant at grid resolution if you will have many times larger grid of pixels you will see a wide waves of color, grid is not more important for visualisation here as with normal bitmap thing - it does not produce the effect only downsamples it - so i still not see where is interference here i do not see it, the image isa an effect of colouring not 

intefrerention (image as i said is 'downsampled' but this is the same like when for example mandelbrot set visualization or raytracing images visualisation)

Edited by fir
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I am impressed with the patience shown here. It's a Moire pattern.

For me it seem s that moire is some broad class of visuals, and this one kind is some specyfic type of fractal - maybe deserves its own name (i dont know, im not sure). For me it is interesting object maybe i will do a little explorer of it later..

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See:

 

https://www.google.no/search?q=moire+pattern&espv=210&es_sm=119&source=lnms&tbm=isch&sa=X&ei=4KTzUqDvDOrMygPYhoGIBw&sqi=2&ved=0CAcQ_AUoAQ&biw=1920&bih=898

 

On any of those pictures:

 

Since the TV that I use with my computer has a resolution that doesn't quite match up with the natural resolution of the graphic card, I get Moire patterns exactly like yours when I have zoomed completely out.  When I zoom in, the pattern disappear.  The pictures are static.  (CTRL + mouse scroll on Mac to zoom, or what you have configured.  Not sure how to activate on Windows any more.)

 

You will probably not see the same result, unless you pick a resolution that does not quite match up with the resolution on the screen, but the reason is the same: ALIASING.  Aliasing makes Moire patterns.

 

Aliasing happens when you show high frequency data on a low(er) frequency medium.

 

Have a look here: http://www.svi.nl/AliasingArtifacts

 

Even TV / video producers avoid having certain clothes to avoid aliasing effects.  You don't often see clothes with high contrast horizontal stripes, for instance: http://www.assetmediagroup.com/what-to-wear-for-video-shoot.html

Edited by aregee
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