From: maria goranovic (
Date: Wed Jun 09 2010 - 11:18:13 CDT

Dear John

It is not entirely clear to me what exactly will be required for the
alternate method .. ? Are you talking about writing some lines to the .dat
that is output by tachyon? Can a transparent background be saved in other
image formats such as tga or tif?

On Wed, Jun 9, 2010 at 5:06 PM, John Stone <> wrote:

> Hi,
> I haven't implemented background-free images for Tachyon yet.
> Actually what this type of feature actually does is add an alpha-channel
> to the image corresponding to the amount of background visible through
> each rendered pixel. While the math involved in computing the alpha
> channel is relatively inexpensive, adding support for it in Tachyon would
> likely mean making changes all throughout the rendering code so it gets
> passed around everywhere, which adds some overhead in cases when you don't
> need it. If you want to superimpose a Tachyon image on a background, an
> alternative way to do this is to load your background image as a texture
> map and put it on a plane at the very back of the view volume, and set
> the material properties for the plane to be entirely diffuse.
> If you're interested in doing something like that, I could probably write
> you a little Tcl script for VMD that would do this by appending commands
> to an existing Tachyon scene file. I won't have time to work on it until
> next week however.
> Cheers,
> John Stone
> On Wed, Jun 09, 2010 at 04:33:25PM +0200, maria goranovic wrote:
> > Is it possible to render images to background-free .png format images?
> > From the mailing list, it seems that it is not included in the
> > downloadable binary formats?
> >
> > --
> > Maria G.
> > Technical University of Denmark
> > Copenhagen
> --
> NIH Resource for Macromolecular Modeling and Bioinformatics
> Beckman Institute for Advanced Science and Technology
> University of Illinois, 405 N. Mathews Ave, Urbana, IL 61801
> Email: Phone: 217-244-3349
> WWW: <>
> Fax: 217-244-6078

Maria G.
Technical University of Denmark