Hello:

I am creating an animation with a metallic object which will be used later with
other (live action) film footage.  I've created the object and have the
background set to "background { color Green }" and found this works well with
my video editing software.

However, when I run the animation I notice the metallic surface of the object
picks up the Greenish color of the background.  To prevent this, I chose these
settings:
                pigment { LightGray }
                finish { ambient .95
                diffuse .1
                specular 1
                roughness .1
                //metallic  <- decided against this at some point
                reflection {
                  .015
                  metallic
                  }
                }

But I am not happy with the result as it looks plain and gray.  What settings
should I use to simulate an aluminum, metallic (only somewhat shiny) surface?

Thanks,

James

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"james lake" <gum### [at] sprintmailcom> wrote:
> However, when I run the animation I notice the metallic surface of the object
> picks up the Greenish color of the background.  To prevent this, I chose these
> settings:
>
> But I am not happy with the result as it looks plain and gray.  What settings
> should I use to simulate an aluminum, metallic (only somewhat shiny) surface?

The only way to get a convincing metallic look is to have the object in question
reflect something.

I'd recommend placing a large around the scene and mapping a 360 degree
photograph onto it (a "light probe"), ideally using a HDR image (POV 3.6 does
not support this, but MegaPOV 1.2.1 or the 3.7 beta will both do the job). Use
an "ambient 1 diffuse 0 specular 0" finish, and the "no_image" and "no_shadow"
keywords.

This will make sure the sphere will show up in reflections, but neither cast
shadows nor be visible in the background.

BTW, if you leave the background completely blank and use the PNG output format,
you can directly generate an alpha channel, without resorting to a "green box"
approach. (IIRC you need to set some additional .ini option for this, but I
don't remember exactly which.)

Post a reply to this message

"james lake" <gum### [at] sprintmailcom> wrote:
> However, when I run the animation I notice the metallic surface of the object
> picks up the Greenish color of the background.  To prevent this, I chose these
> settings:

You probably want to play with no_image, no_reflection, and no_shadow keywords.
Use two backdrops: a green one with no_reflection so it is not reflected, and a
second with no_image so you only see its reflection.  Attached is a very quick
example of how you could use this to achieve a green backdrop on a reflective
object.

 - Ricky


camera{
    location <0,2,-3>
    look_at <0,1,0>
}
light_source{<1,10,-1> rgb 1 shadowless}

//Ground + sky:
sphere{0,1
    pigment{
        gradient y
        color_map{
            [0 rgb <0.8,0.5,0.3>*0.9 ]
            [0.499 rgb <0.8,0.5,0.3>*0.7 ]
            [ 0.5 rgb <0.6,0.6,1.0> ]
            [ 1 rgb <0.2,0.2,0.7> ]
        }
        scale y*2
        translate -y
    }
    finish{ambient 0}
    scale 50
    no_image
}

//Reflective sphere:
sphere{y,1
    pigment{rgb 1}
    finish{
        reflection 0.8
    }
    finish{ambient 0}
    no_reflection
}

//Green background:
plane{-z,-10
    pigment{ rgb <0,1,0> }
    finish{
        ambient 1
        diffuse 0
    }
    no_reflection
    no_shadow
}

Post a reply to this message

On Sun, 11 Jan 2009 15:16:07 EST, "james lake" <gum### [at] sprintmailcom> wrote:

> I've created the object and have the
>background set to "background { color Green }" and found this works well with
>my video editing software.

This is just a shot in the dark, untested. 
Instead of setting the background to green try putting a green plane behind your
object and use "no_shadow" and "no_reflection".

BTW welcome James.
-- 

Regards
     Stephen

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"james lake" <gum### [at] sprintmailcom> wrote in message 
news:web.496a5387cd24b95e7352b36c0@news.povray.org...
> Hello:
>
> I am creating an animation with a metallic object which will be used later 
> with
> other (live action) film footage.  I've created the object and have the
> background set to "background { color Green }" and found this works well 
> with
> my video editing software.
>
> However, when I run the animation I notice the metallic surface of the 
> object
> picks up the Greenish color of the background.  To prevent this, I chose 
> these
> settings:
>   ... snip ...
>
> But I am not happy with the result as it looks plain and gray.  What 
> settings
> should I use to simulate an aluminum, metallic (only somewhat shiny) 
> surface?
>

Any reflective settings are generally going to pick up the background color. 
You may therefore wish to consider the following alternatives in some sort 
of combination (some of which I notice are covered by clipka and Ricky. They 
obviously type quicker than I do :o) ):

Ideally load frames of your live-action film footage as a background so that 
you get credible reflections in your metallic object.
Otherwise load a still image with the same sort of colors and features to 
get reasonable but fake reflections.

To do this you can add a plane using an image_map as the pigment and you can 
use the 'no_image' object modifier on the plane so that you can make this 
'false' background image disappear except for through reflections.

Use a transparent background (rgbt 1) and an output file format that 
supports a transparency channel (an alpha channel) so that you don't need to 
eliminate the background as a post-processing step. I believe that Targa and 
PNG formats support an alpha channel. You can set the file type as an ini 
file option (Output_File_Type) or using the +Fxn command-line option. To 
activate the alpha channel (which is off by default) you'll also need to set 
Output_Alpha to 'on' in the ini file (or use the +UA command-line option).

Regards,
Chris B.

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I couldn't find anything on HDR illumination in the release notes for 3.7 beta,
although here's the mega-pov tutorial:
http://megapov.inetart.net/manual-1.2/tutorials_hdri.html

with some documentation:
http://megapov.inetart.net/manual-1.2/patterns.html#hdr

I don't know if syntax is compatible.

I think this is relevant to the alpha-channel background:

http://www.povray.org/beta/

   Alpha Changes
   -------------

   Some changes have been made to the way alpha is handled when +UA is activated.
   Firstly, in previous versions, specifying a background with the background
   keyword would by default supply a background with transmit set to 1.0 (i.e.
   fully transparent provided that +ua is being used). This is no longer the case.

   While the default background is transparent, any background specified in a
   scene file (unless 3.6 or earlier compatibility is being used) will now be
   opaque unless transmit is explicitly given. (In other words, use rgbft<>
   rather than rgb<> in the background statement if you want the old behaviour).

   Secondly, the way that objects are blended with the background has changed.
   Previously the color of the background was not taken into account when
   calculating effects of transmission through translucent objects when +ua is
   in effect (i.e. where the background could otherwise have been seen through
   the object). Now, however, the background color is taken into account, even
   if it is not otherwise visible. (In other words, blending is performed in the
   same way regardless of the presence of background transparency).

   Note that this change is not affected by the #version directive, so it may
   change the appearance of scenes written for version 3.6 and earlier. We will
   monitor feedback on this from beta testers to evaluate the impact of this.

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Dan Connelly wrote:

> I couldn't find anything on HDR illumination in the release notes for 
> 3.7 beta

Changes between 3.7.beta.7 and 3.7.beta.8:

   "Added HDR file support (RGBE, as used in Radiance)."

It does seem rather terse ;)

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