rendering transparent object

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  11 November 2009
rendering transparent object

OK, I believe this a completely blond moment even though I have brown hair. I am rendering a bottle with no background so that I will get an alpha that allows you to see thru the object in Photoshop. For some reason the alpha is solid around the bottle but does not mask out any of the transparency. What do I have turned off or on!

Thanks,

Eric
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Eric Decker

Retro EIAS user
 
  11 November 2009
try opening in After Effects

Hi Eric,

Try opening your rendered bottle in After Effects (if you have it). If you do, be sure to put a "solid" color layer beneath the bottle so you can see how the transparency is supposed to look.

Joe T
 
  11 November 2009
Hi Joe,

Thanks for the reply, I do not think I elaborated enough. I get the alpha and the bottle but the alpha only masks out around the bottle but not the transparency of the glass itself. So the bottle instead of being transparent like glass is composited with black even though there is no background. My end result is I need the bottle without any background and be able to see through the glass.

Thanks,

Eric
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Eric Decker

Retro EIAS user
 
  11 November 2009
There is no way for raytraced transparency to produce a proper alpha channel.
The ray must ultimately return some color.

If you have After Effects- you may be able to create a virtual green screen by rendering with the proper background color. This color will be visible through the glass, and you should be able to composite using chroma key.

Dave
 
  11 November 2009
Eric,

You might also try adding the background to the 3D scene if that is possible for your shot. That will give you the most realistic refractions through the glass. Another option is a mix of what I'm suggesting and what Dave has suggested. That way you get some refracted items as well as an alpha that you can finesse in the composite.

Bill
 
  11 November 2009
Hi guys,

Thanks for the responses. I think the key was the raytraced rendering. I need the bottle to have a transparency to it since it will be layered on top of a background in a Flash application. The user will be able to move it so it needs to show the back ground behind it. Fortunately these are pretty small so I can use phong render for these and achieve the look I need.

I could have sworn that I did this on a project a couple years ago but when I just looked at the files again I saw that I did indeed use a colored background to key.

Thanks!

Eric
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Eric Decker

Retro EIAS user
 
  11 November 2009
Could you create a luma matte pass by, say, using a black background and that bottle using a white transparent material with luminance? Later in AE you could derive an alpha from that.
 
  11 November 2009
You might as well check on v7 tutorials on creating alpha raytrace transparencies.
http://eitechnologygroup.com/support/tutorials
 
  11 November 2009
I did go to the tutorial yesterday but alas the link is broken for that one. But since you mentioned it I just dug out my V7 dvd though so I can see it there.

Thanks!

Eric
__________________
Eric Decker

Retro EIAS user
 
  11 November 2009
Oh dear!

I'll email Phil about that.
Ian
 
  11 November 2009
I sent an email about the broken link.

I also figured out my little problem. I had selected "use raytrace" in the transparency main options. After I deselected it I had transparent glass again while raytrace rendering!

Thanks all.
__________________
Eric Decker

Retro EIAS user
 
  11 November 2009
Originally Posted by edecker: I sent an email about the broken link.

I also figured out my little problem. I had selected "use raytrace" in the transparency main options. After I deselected it I had transparent glass again while raytrace rendering!

Thanks all.

Yeah that worked for me too but i dont get the refraction from the glass or the caustics which requires raytrace to be activated. I love caustics from EIAS are one of the best features on that beast
 
  11 November 2009
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