Hello Alain,

thanks for your answer.

Alain <ele### [at] netscapenet> wrote:
> This is due to the fact that area_light are composed of several point_lights
> disposed in a regular array. Some shadowed points may be in view of all of
> those points.

Yes, I figured out this was the problem, but I am not sure how to get rid of
it ;)

> The use of jitter can help hide this, as for each points tested, the location
> of  each element is slightly shifted randomly from it's original position for
> the shadow evaluation. This random noise is normaly unnoticeable.

I did use jitter, too.
Well, let me clarify, this is my test scene:


#include "colors.inc"
#include "textures.inc"
plane { y, 0
  pigment { rgb .8 }
  finish { reflection .05 }
}
cylinder { <0,0,0>,<0,1,0>,.03
  texture { Chrome_Metal }
}
#declare qualight=clock;
light_source { <6, 4, 0> White
  area_light <3, 0, 0>, <0, 0, 3>, qualight, qualight
  jitter
  circular orient
}
camera {
  location <0, 2, -2>
  look_at <-1.2, 0, 0>
}


You can see the result here: http://www.tasuki.org/povray/arealights.png

For some number of lights, it looks ok... but the problem appears again when
I have more sticks at different distances from the area light...

Post a reply to this message

"tasuki" <nomail@nomail> wrote:
> Hello Alain,
>
> thanks for your answer.
>
> Alain <ele### [at] netscapenet> wrote:
> > This is due to the fact that area_light are composed of several point_lights
> > disposed in a regular array. Some shadowed points may be in view of all of
> > those points.
>
> Yes, I figured out this was the problem, but I am not sure how to get rid of
> it ;)
>
> > The use of jitter can help hide this, as for each points tested, the location
> > of  each element is slightly shifted randomly from it's original position for
> > the shadow evaluation. This random noise is normaly unnoticeable.
>
> I did use jitter, too.
> Well, let me clarify, this is my test scene:
>
>
> #include "colors.inc"
> #include "textures.inc"
> plane { y, 0
>   pigment { rgb .8 }
>   finish { reflection .05 }
> }
> cylinder { <0,0,0>,<0,1,0>,.03
>   texture { Chrome_Metal }
> }
> #declare qualight=clock;
> light_source { <6, 4, 0> White
>   area_light <3, 0, 0>, <0, 0, 3>, qualight, qualight
>   jitter
>   circular orient
> }
> camera {
>   location <0, 2, -2>
>   look_at <-1.2, 0, 0>
> }
>
>
> You can see the result here: http://www.tasuki.org/povray/arealights.png
>
> For some number of lights, it looks ok... but the problem appears again when
> I have more sticks at different distances from the area light...

Your area light is *way* too wide compared to the item it shines on. You've
got a cylinder 0.03 in radius and, in the 50 lights scenario, a light every
0.06. Obviously you end up with two shadows divided by a lighter zone.
Simply cut down on the area light size (i.e. <3, 0, 0>, <0, 0, 3> ) to
something more in tune with the target object size.

Post a reply to this message

Hello!

> Your area light is *way* too wide compared to the item it shines on. You've
> got a cylinder 0.03 in radius and, in the 50 lights scenario, a light every
> 0.06. Obviously you end up with two shadows divided by a lighter zone.
> Simply cut down on the area light size (i.e. <3, 0, 0>, <0, 0, 3> ) to
> something more in tune with the target object size.

I see...

But when I make the area smaller, I get too sharp shadows. I'd like really
soft shadows... is there any way of creating soft shadows with thin
objects?

Post a reply to this message

"tasuki" <nomail@nomail> wrote:
> Hello!
>
> > Your area light is *way* too wide compared to the item it shines on. You've
> > got a cylinder 0.03 in radius and, in the 50 lights scenario, a light every
> > 0.06. Obviously you end up with two shadows divided by a lighter zone.
> > Simply cut down on the area light size (i.e. <3, 0, 0>, <0, 0, 3> ) to
> > something more in tune with the target object size.
>
> I see...
>
> But when I make the area smaller, I get too sharp shadows. I'd like really
> soft shadows... is there any way of creating soft shadows with thin
> objects?

Have you tried moving the light further away from the object?

Stephen

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tasuki wrote:

> But when I make the area smaller, I get too sharp shadows. I'd like really
> soft shadows... is there any way of creating soft shadows with thin
> objects?

Well, if you go to 150 lights the spacing is at least smaller than
the object width and the light streak in the center goes away. Also,
you can use a lot of lights in the z direction and less lights for
the other axis (although it feels like a 30x30 grid renders a lot
faster than 1x150).

Post a reply to this message

tasuki nous apporta ses lumieres en ce 2007/09/14 05:12:
> Hello Alain,
> 
> thanks for your answer.
> 
> Alain <ele### [at] netscapenet> wrote:
>> This is due to the fact that area_light are composed of several point_lights
>> disposed in a regular array. Some shadowed points may be in view of all of
>> those points.
> 
> Yes, I figured out this was the problem, but I am not sure how to get rid of
> it ;)
> 
>> The use of jitter can help hide this, as for each points tested, the location
>> of  each element is slightly shifted randomly from it's original position for
>> the shadow evaluation. This random noise is normaly unnoticeable.
> 
> I did use jitter, too.
> Well, let me clarify, this is my test scene:
> 
> 
> #include "colors.inc"
> #include "textures.inc"
> plane { y, 0
>   pigment { rgb .8 }
>   finish { reflection .05 }
> }
> cylinder { <0,0,0>,<0,1,0>,.03
>   texture { Chrome_Metal }
> }
> #declare qualight=clock;
> light_source { <6, 4, 0> White
>   area_light <3, 0, 0>, <0, 0, 3>, qualight, qualight
>   jitter
>   circular orient
> }
> camera {
>   location <0, 2, -2>
>   look_at <-1.2, 0, 0>
> }
> 
> 
> You can see the result here: http://www.tasuki.org/povray/arealights.png
> 
> For some number of lights, it looks ok... but the problem appears again when
> I have more sticks at different distances from the area light...
> 
> 
> 
Let see:
clock goes from 0 to 1, qualight = clock. As it is, on the firse frame I get an 
error about a size of zero. You need to multiply clock by some value then add 
something to that. Something like:
#declare Qualight = clock*20 +3;

Another aproach, would be to use radiosity with a high ambient "light source".
Replace your light with:
sphere{<6,4,0>,1.5 texture{pigment{rgb 2}finish{ambient 10}}
and add:
global_settings{radiosity{count 500 error_bound 0.7 low_error_factor 0.2}}
and
#default{finish{ambient 0 diffuse 1}}

-- 
Alain
-------------------------------------------------
I find that the harder I work, the more luck I seem to have.
Thomas Jefferson

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> clock goes from 0 to 1

Actually I use clock just to be able to pass the number of lights as a
command line argument... So it is usually something like 29. I am not sure
if there's any other way to pass an argument :-)

Post a reply to this message

tasuki wrote:
>>clock goes from 0 to 1
> 
> 
> Actually I use clock just to be able to pass the number of lights as a
> command line argument... So it is usually something like 29. I am not sure
> if there's any other way to pass an argument :-)

You can declare a numeric variable and assign it a value from
the command line using something like "Declare=NUMLIGHTS=29".

Post a reply to this message

"tasuki" <nomail@nomail> wrote:
> Hello!
>

Hello! :-)

> > Your area light is *way* too wide compared to the item it shines on. You've
> > got a cylinder 0.03 in radius and, in the 50 lights scenario, a light every
> > 0.06. Obviously you end up with two shadows divided by a lighter zone.
> > Simply cut down on the area light size (i.e. <3, 0, 0>, <0, 0, 3> ) to
> > something more in tune with the target object size.
>
> I see...
>
> But when I make the area smaller, I get too sharp shadows. I'd like really
> soft shadows... is there any way of creating soft shadows with thin
> objects?

Increasing the number of lights seems to be the way to go. Make sure you
have an odd number of lights if the distance between two consecutive lights
(in the area light, that is) isn't smaller than the diameter of your object.
Even then, you probably want to have at least 4 lights in the cylinder
diameter. Assuming you still want a <3,0,0>-wide area light, that would
mean 4/0.06=x/3 --> x=200 lights.

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When mime-encoding, a = is converted to =3D - view the source of an email 
with an equals in it. OPbviously the mail client(s) being used encode the 
subject when they shouldn't (or the server doesn't decode it properly)

"Trevor G Quayle" <Tin### [at] hotmailcom> wrote in message 
news:web.46e96ef23b1d16abc150d4c10@news.povray.org...
> "Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
>> "tasuki" <nomail@nomail> wrote:
>> > Uh, huh... I have no idea how the word "3D" slipped into the subject...
>> >
>> > It should have been just: "Area light + thin object = problem"
>>
>> Another "3D" has been added now!
>>
>> Perhaps you could post an abridged scene as you are using it so it can be
>> assessed better.
>>
>> -tgq
>
> What the heck, it's doing it to me too!  Make it stop! Somebody!
>
> I wonder if it has something to do with the "=" in the subject.  I have
> never seen this before...
>
> -tgq
>
>

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