Hi

I'm getting strange black reflections on shiny balls.I'm usingt mlpov 0.8 
with hdri. Anybody has an idea what is causing this?


The balls consits of two parts an inner ball with the following texture
#declare  lightyellowfinball =   finish { ambient 0 diffuse .0 reflection 
{ <2.3,2.3,1>*1.1*0.9,<0.5,0.5,0.5>*0.9  } }


around this is a second ball slightly thicker
with the following texture map

#declare ttextur=   texture { pigment {rgbt <1,1,1,1>} normal {bumps 1 scale 
.01}};
#if (strcmp(texturepic,"")!=0)
sphere{
0,1+0.001
      texture { uv_mapping
        image_pattern { gif texturepic  }
        texture_map {
                [0 uv_mapping ttextur]
                [1 uv_mapping textur scale 1/mapscale]
                }

         scale mapscale
         translate <0,1.02*mapscale,0>

        }
rotate <0,15,0>
translate <0,1,0>
}
this seems to work fine for the balls themselves, but the transparent part 
of the reflections go black... When i render the same pic without the second 
ball the reflections don't go black

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Attachments:
Download 'HDRItest3.jpg' (70 KB)

Preview of image 'HDRItest3.jpg'

I would guess you're hitting the max trace limit. Try adding this:

global_settings {max_trace_level 10}

(IIRC the default is 5. Check the documentation...)

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yep that seems to work.
I don't really get why the trace level needs to increase when there is a 
transparent layer around the shiny finish,but anyhow problem  is solved now.
"Orchid XP v3" <voi### [at] devnull> wrote in message 
news:45bb6f64$1@news.povray.org...
>I would guess you're hitting the max trace limit. Try adding this:
>
> global_settings {max_trace_level 10}
>
> (IIRC the default is 5. Check the documentation...)

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"Johan Feyaerts" <joh### [at] nospamhotmailcom> wrote in message
news:45bb72b8@news.povray.org...
> yep that seems to work.
> I don't really get why the trace level needs to increase when there is a
> transparent layer around the shiny finish,but anyhow problem  is solved
now.

Max trace is the amount of objects that the light ray is allowed to
reflect/pass through before it returns the colour as black. With you putting
a transparent layer around each ball, you've doubled the number of
interactions (once for the transparent layer, once for the reflection)

I've got a scene that uses trees with alpha-mapped transparency and water
and because of those two, I need a max trace of about 90. If I remove the
trees, it's more like 10. If I remove the water, it's somewhere around 40.

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Thanks, now I understand. Didn't know that a transparent layer also 
increased the # of objects reflected passed.

"Gail Shaw" <initialsurname@sentech sa dot com> wrote in message 
news:45bb779a@news.povray.org...
>
> "Johan Feyaerts" <joh### [at] nospamhotmailcom> wrote in message
> news:45bb72b8@news.povray.org...
>> yep that seems to work.
>> I don't really get why the trace level needs to increase when there is a
>> transparent layer around the shiny finish,but anyhow problem  is solved
> now.
>
> Max trace is the amount of objects that the light ray is allowed to
> reflect/pass through before it returns the colour as black. With you 
> putting
> a transparent layer around each ball, you've doubled the number of
> interactions (once for the transparent layer, once for the reflection)
>
> I've got a scene that uses trees with alpha-mapped transparency and water
> and because of those two, I need a max trace of about 90. If I remove the
> trees, it's more like 10. If I remove the water, it's somewhere around 40.
>
>

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Johan Feyaerts nous apporta ses lumieres en ce 27-01-2007 10:41:
> yep that seems to work.
> I don't really get why the trace level needs to increase when there is a 
> transparent layer around the shiny finish,but anyhow problem  is solved now.
> "Orchid XP v3" <voi### [at] devnull> wrote in message 
> news:45bb6f64$1@news.povray.org...
>> I would guess you're hitting the max trace limit. Try adding this:

>> global_settings {max_trace_level 10}

>> (IIRC the default is 5. Check the documentation...) 


Each time you reflect on a sphere, the trace level goes up by 3: 1 getting into 
the transparent outer shell, 1 relecting on the iner reflective part, and 1 more 
geting OUT of the transparent shell.
If the reflection hit 2 balls, it register 6 levels, 9 if it hits 3 balls. Add 
one to reatch the background or any surrounding object.
So, for one ball, you need a Max_trace_level of at least 4. For 2, you need at 
least 7, and 10 if you hit 3.
In your case, I'd go up to arount 15 or 17. For that scene, I'd go up to the max 
of 255 and set adc_bailout to 1/128 or even as large as 1/64.
Note that there are many more max_trace_level related black spots than those you 
spotted. I can find at least 8 more, and I probably missed some.

-- 
Alain
-------------------------------------------------
EVERYTHING HAS A GENDER

You may not know this but many nonliving things have a gender...

An Hourglass is Female, because over time, the weight shifts to the bottom.

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I changed the settings to
global_settings {
  radiosity {
    pretrace_start 0.08           // start pretrace at this size
    pretrace_end   0.04           // end pretrace at this size
    count 60                      // higher -> higher quality (1..1600) [35]
    nearest_count 5               // higher -> higher quality (1..10) [5]
    error_bound 1.8               // higher -> smoother, less accurate [1.8]
    recursion_limit 5             // how much interreflections are 
calculated (1..5+) [3]
    low_error_factor .5           // reduce error_bound during last pretrace 
step
    gray_threshold 0.0            // increase for weakening colors (0..1) 
[0]
    minimum_reuse 0.015           // reuse of old radiosity samples [0.015]
    brightness 1                  // brightness of radiosity effects (0..1) 
[1]

//    adc_bailout 0.01/2
    adc_bailout 1/64
    normal on                     // take surface normals into account [off]
  }
  max_trace_level 26

This seems satisfactory to me, most disturbing black spots seem to be gone 
now.
I plan to do an animation with this scene (hopefully ready by christmas 
2007), so I guess I'll have to reduce the trace level to something like 17 
make it faster
Thanks for the advice.


> Each time you reflect on a sphere, the trace level goes up by 3: 1 getting 
> into
> the transparent outer shell, 1 relecting on the iner reflective part, and 
> 1 more
> geting OUT of the transparent shell.
> If the reflection hit 2 balls, it register 6 levels, 9 if it hits 3 balls. 
> Add
> one to reatch the background or any surrounding object.
> So, for one ball, you need a Max_trace_level of at least 4. For 2, you 
> need at
> least 7, and 10 if you hit 3.
> In your case, I'd go up to arount 15 or 17. For that scene, I'd go up to 
> the max
> of 255 and set adc_bailout to 1/128 or even as large as 1/64.
> Note that there are many more max_trace_level related black spots than 
> those you
> spotted. I can find at least 8 more, and I probably missed some.

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Attachments:
Download 'HDRItest3.jpg' (148 KB)

Preview of image 'HDRItest3.jpg'

Johan Feyaerts wrote:
> ...
> around this is a second ball slightly thicker
> with the following texture map
> ...

You should be able to get rid of the outer sphere by using layered
textures: http://povray.org/documentation/view/3.6.1/356/
This should render a bit faster and work without increasing the
max_trace_level.

HTH,
Florian

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I think I tried that already but pov protested that image maps could not be 
combined with texture maps.  Currently I only use one of both at the same 
time but I may combine them when I map the metallic image and a picture on 
the same ball in  the macro.
I'm currently just fooling around with textures, image maps, alfa channels, 
finishes , hdri etc. to learn how to use these things. I'll probably have to 
rewrite the macro for more efficiency when I try to do an animation, so 
thanks for the tip.

"Florian Brucker" <tor### [at] torfboldcom> wrote in message 
news:45bbd81d$1@news.povray.org...
> Johan Feyaerts wrote:
>> ...
>> around this is a second ball slightly thicker
>> with the following texture map
>> ...
>
> You should be able to get rid of the outer sphere by using layered
> textures: http://povray.org/documentation/view/3.6.1/356/
> This should render a bit faster and work without increasing the
> max_trace_level.
>
> HTH,
> Florian

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Johan Feyaerts wrote:
> I think I tried that already but pov protested that image maps could not be 
> combined with texture maps.

An image_map is a pigment type, which is part of a texture.  So you 
shouldn't try to combine the two.

Instead, declare the image map as the pigment of a complete texture, and 
layer that with another complete texture.

...Chambers

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