VMD-L Mailing List

From: John Stone (johns_at_ks.uiuc.edu)
Date: Thu Jul 17 2008 - 16:31:06 CDT

Hi,
  The Tachyon flags that reproduce the OpenGL or GLSL renderings in VMD are:
"-aasamples 4 -trans_vmd -mediumshade"

The "-rescale_lights 0.8 -add_skylight 0.9" flags enable ambient occlusion
lighting, which has the effect of enabling shadows, which aren't rendered
at all when "-mediumshade" is used. This is an important distinction, as
you'll definitely tend to get a somewhat darker image than when there are
no shadows at all. In order to counteract this, one can either enable
more lights, use brighter colors (e.g. either by selecting brighter
colors in the graphics window or by editing the colors themselves
in the color window...), or use a higher value with the -rescale_lights
parameter. Variations of this sort will reduce the overall darkening of
the scene, though some is unavoidable as that's the nature of shadows :-)

I should note that this shadow effect is completely independent of the VMD
background color, so that's not really a contributing factor at all.

Let me know if you have more questions on this.

Cheers,
  John Stone
  vmd_at_ks.uiuc.edu

On Thu, Jul 17, 2008 at 02:15:48PM -0700, Lixia Jin Day wrote:
> John,
>
> Attached figure is one of the figures generated. I don't remember
> exactly the lights I used, probably "-rescale_lights 0.8 -add_skylight
> 0.9"
> I got my best figure by using "-mediumshade" only, which is almost the
> same as in VMD.
> I also attached the dat file (compressed into rar) for reference.
>
> Thank you for helping.
>
> Lixia
>
>
> On Tue, Jul 15, 2008 at 11:46 PM, John Stone <johns_at_ks.uiuc.edu> wrote:
> >
> > Hi,
> > Can you send me an email with the images in question?
> > I'm happy to give you suggestions on getting good results
> > from VMD/Tachyon. One question I have that may elucidate your
> > problem is whether or not you're using depth cueing, and also
> > whether you ran the rendering manually (outside of VMD) or
> > automatically from the VMD File->Render menu item.
> >
> > Thanks,
> > John Stone
> > vmd_at_ks.uiuc.edu
> >
> > On Fri, Jul 11, 2008 at 11:06:30AM -0700, Lixia Jin Day wrote:
> >> I redered my figure using tachyon, then re-rendered it with tachyon_WIN32. Since the figure has a black background, the figure after re-rendering looks very dark. I tried a couple options but didn't get a good result. Do you know what is the best option to render a black background figure using tachyon? Thank you!
> >>
> >> Lixia
> >
> > --
> > 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: johns_at_ks.uiuc.edu Phone: 217-244-3349
> > WWW: http://www.ks.uiuc.edu/~johns/ Fax: 217-244-6078
> > 

-- 
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: johns_at_ks.uiuc.edu                 Phone: 217-244-3349
  WWW: http://www.ks.uiuc.edu/~johns/      Fax: 217-244-6078