Hello. I've been modelling a bit on a pice of decoration here, one of the few
real-life objects I've been doing after measurements and aiming for a good scale
of things..

I'm rather satisfied with the model as  it is, but I have a really hard time
getting the texture to look "right" .

It is a silver texture, fairly dull (i've got this one). But then the hard part
comes. It's brushed in a spiral pattern (a disc in the x-z plane, radius approx
5 pov). I've tried using the spiral patterns, but I can't seem to get them thin
enough to look good without a great deal of "interference"(the best description
I have) 

does anyone have tips/ideas for a solution to this ?
-- 
//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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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.

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.

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.

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

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.

steve

Spider wrote:

> Hello. I've been modelling a bit on a pice of decoration here, one of the few
> real-life objects I've been doing after measurements and aiming for a good scale
> of things..
>
> I'm rather satisfied with the model as  it is, but I have a really hard time
> getting the texture to look "right" .
>
> It is a silver texture, fairly dull (i've got this one). But then the hard part
> comes. It's brushed in a spiral pattern (a disc in the x-z plane, radius approx
> 5 pov). I've tried using the spiral patterns, but I can't seem to get them thin
> enough to look good without a great deal of "interference"(the best description
> I have)
>
> does anyone have tips/ideas for a solution to this ?
> --
> //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"

Post a reply to this message

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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Are you talking about brushed metal?  That's what those anisotropic shaders everyone
is always talking about do.  I think they require uv coordinates, but a spherical
mapping technically does have those, so it could probably be added to POV-Ray.  But
I digress...

If you can get the spiral correct and increase the frequency below screen res, then
super high AA should create the desired effect.  Just use Adaptive sampling and an
AA depth of like 4 or 5 and a threshold of .01 or something like that.  Then take a
trip somewhere while it renders. ;)

-Mike

Spider wrote:

> Hello. I've been modelling a bit on a pice of decoration here, one of the few
> real-life objects I've been doing after measurements and aiming for a good scale
> of things..
>
> I'm rather satisfied with the model as  it is, but I have a really hard time
> getting the texture to look "right" .
>
> It is a silver texture, fairly dull (i've got this one). But then the hard part
> comes. It's brushed in a spiral pattern (a disc in the x-z plane, radius approx
> 5 pov). I've tried using the spiral patterns, but I can't seem to get them thin
> enough to look good without a great deal of "interference"(the best description
> I have)
>
> does anyone have tips/ideas for a solution to this ?
> --
> //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"

Post a reply to this message