VMD-L Mailing List

From: Pawel Kedzierski (pawel.kedzierski_at_pwr.edu.pl)
Date: Tue Mar 02 2021 - 14:58:22 CST

W dniu 02.03.2021 o 20:43, Pacci Evaristo, Felipe Fabricio pisze:
> Hi there,
>
> I've been trying to solve this problem for a while now. I'm on macOS
> Catalina. I've been trying to render an image background-free on VMD.
> I've been trying to use POV-Ray for that. I found tutorials where
> people have used the following line in the Render Command box in the
> GUI interface (except for the link to the POV-Ray executable):
>
> '/Users/felipepacci/Downloads/PovrayCommandLineMacV2//Povray37UnofficialMacCmd'
> +W%w +H%h -I%s -O%s.png +D +X +A +FN +UA -res 1600 900
>
> This render does produce a .pov file; however, when I try to render it
> into a .tga file in POV-Ray, the output .tga image still contains a
> background. Am I missing something really obvious here?

There are three important details to get a render with transparent
background with POV-Ray. One is that the output format must be PNG, and
this is requested by the option +FN. Second, the transparency (alpha
channel) must be requested with option +UA. Those two you seem to have
correct. The third non-obvious detail is that you have to switch off
"Depth Cueing" in the VMD Display menu.

To clarify, it is not POV-Ray which produces the .pov file, it's VMD.
The .pov file is the input to POV-Ray which is provided via the option
-I (VMD replaces %s with the actual name).

I guess your command above crashes without producing the output PNG
because of spurious, wrong option at the end: -res 1600 900, which is
not recognized by POV-Ray. The actual resolution of the image is
provided to POV-Ray with the options +W and +H, where VMD substitutes %w
and %h with the window width and height, respectively.

If you want an arbitrary resolution image, just run POV-Ray in a
terminal like this:

/Users/felipepacci/Downloads/PovrayCommandLineMacV2//Povray37UnofficialMacCmd
+W1600 +H900 -Iyourfile.pov -Ooutputimage.png +D +X +A +FN +UA

Note however that you should know the original size of the window and
scale it appropriately to preserve the aspect ratio, or you will get
distorted image.

Fortunately, you will find the command with width and height in the
comments at the very beginning of the .pov file (which is a simple text
file).

Disclaimer - I do not know Mac OS so I only assume, that my knowledge on
VMD and POV-Ray for Linux is transferable.

HTH,

Pawel

>
> I'm open to other methods that don't include POV-Ray to generate my
> background-free image.
>
> Thank you beforehand for any help provided,
>
> *Felipe Fabricio Pacci Evaristo*
> *Mobile:* +1(773)569-2978
> *Email:* felipepacci_at_gmail.com <mailto:felipepacci_at_gmail.com>
> *Skype:* felipepacci