Steve wrote:
> 
> Spider, I can't tell exactly without the code, but it sounds like you are
> experiencing a moire pattern. This is the effect where 2 frequencies are close
> together and produce an undesirable harmonic. When the frequencies are linear, the
> solution is to angle one relative to the other about 30 degrees.
ok. This was interesting to read. And, the pattern isn't perfectly circular, but
spiral.

> However, yours sounds like a circular frequency where the pattern in the art is
> harmonizing with the pattern of the screen pixels. To test this, render at a higher
> resolution to see if the effect changes.
Been there, done that :-)
I get the desired effect if i keep a 1.33333 ratio and have a width of 2500 ..
overkill...
 
> There is no known method to elimate moire where pixels are used, all we can do is
> try to minimize the effect by making the harmonics pleasing rather than
> undesireable. This is done using 4 frequencies in the printing business. In the
> case of a frequency that has no direction, like the grooves in an old record, you
> cannot employ the angling technique.
Ok. Then I can :-)
> 
> A secondary improvement might be achieved by altering one of the frequencies. The
> frequency of your monitor might be 72 dpi and the frequency of your art might be
> 143 dpi producing an undesirable harmonic along the 45 degree angle. Try doing your
> art at a frequency that is in golden proportion to the screen frequency ( ( sqrt 5
> ) +1 ) / 2
Hmm,  this is interesting, but will only solve things on my system, not in the
image as whole.

> With a circular pattern you'll probably never eliminate the effect. However, in an
> animation the effect can be exploited by making it change over time.
Yep :-)
 

Thanks for the information on the problem. I realise there isn't much I can do
to get the desired effect with this screen, but at least I know how to prevent
it in other scenes.


-- 
//Spider    --  [ spi### [at] bahnhofse ]-[ http://www.bahnhof.se/~spider/ ]
And the meek'll inherit what they damn well please
	Get ahead, go figure, go ahead and pull the trigger
		Everything under the gun
			--"Sisters Of Mercy" -- "Under The Gun"

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