More testing with VMD and Tachyon
I’m still testing out some of the advanced features of using Tachyon to render nice images of biological macromolecules. I came across these beautiful images of bacteria which are able to consume radioactive waste, and decided to tinker a bit to see if I could get something similar out of VMD.
First of all I loaded in my molecule and set it up similar to the exercises from the other day: white background, surface representation, diffuse material. I also added the Depth Cue feature of VMD, which adds a fog which increases in density with depth. This helps to add a bit of a 3D feel to the representation. I also played around with the various lights, settling on having lights 0 & 2 on.
I rendered the image with:
"/usr/local/lib/vmd/tachyon_LINUX" -aasamples 4 -rescale_lights 0.3 -add_skylight 0.9 %s -format TARGA -o %s.tga
Note: this takes about 8 minutes to render on my laptop at about 700×700 resolution.
If my understanding is correct, this should give a scene that is dominated a fair bit by the skylight parameter, and this is more or less the case. The image, while interesting in some ways, is far too bright!
Let’s drop the skylight down then:
"/usr/local/lib/vmd/tachyon_LINUX" -aasamples 4 -rescale_lights 0.3 -add_skylight 0.6 %s -format TARGA -o %s.tga
Well that darkened the shadows a bit, but the overall image is still way too bright. How about dropping the lights?
"/usr/local/lib/vmd/tachyon_LINUX" -aasamples 4 -rescale_lights 0.1 -add_skylight 0.6 %s -format TARGA -o %s.tga
Well, still far too light. What’s happening is that the depth cue fades the image to the background color (in this case white) as it goes. Let’s drop the depth cue density in order to cut back on the lightening. This setting is found in Display–>Display Settings. I adjusted it to a value of 0.15, still using the Exp2 function for the density. When I rendered this (using the same settings as the last one above, it looked OK, but not fantastic. Mostly it was just “flat”, if that makes sense - not a lot of visual appeal. I rescaled the lights back up to 0.3, and this was better.
Something still isn’t “there”, though. To be sure, the tachyon renders look nice, but I just don’t feel like this is the best that can be done. I’ll have to keep toying with it.
