VMD-L Mailing List
From: John Stone (johns_at_ks.uiuc.edu)
Date: Wed Jan 28 2015 - 11:12:44 CST
With vector graphics formats like PostScript, PDF, or SVG, you can
generate crisp lines and polygon boundaries, but if what is being drawn
is a 3-D object, the best they can do is provide per-vertex colors and
perform interpolation within triangles, or gradients in the case of circles
or other shapes. If one zooms way in on one of those figures, these
formats can't generate new vertices or generate higher resolution triangle
meshes to compensate. So, while vector graphics formats are ideal for
line-drawn geometry, in practice they aren't really a solution for images
that involve 3-D lighting, specular reflections, etc.
To my knowledge, the most faithful reproduction that an SVG, PS, or PDF
vector graphics image would be able to supply would be equivalent to an
OpenGL 1.x rendering with only per-vertex colors. If one was to use any
texture mapping to compensate for these limitations, it ends up with the
same fixed-resolution limitations that a raster image has.
I don't think there's any way to capture things like specular
reflections or other pixel-rate lighting effects with such formats.
PostScript is actually a fairly complete language, so in principle you
could make the printer actually do pixel-rate shading by writing some
hideously complex PostScript code, but I don't think this is true of
SVG or other simpler vector graphics formats.
The 3-D scene files used by POV-Ray or Tachyon (or even X3D, VRML, etc)
are really the best way of capturing the scene in a resolution-independent
way, while being independent of VMD itself. These file formats
describe the scene as a set of perfect geometric objects, but they can
be converted to a raster image of arbitrary resolution at any time by
running the ray tracing engine and setting the output resolution as needed,
and this guarantees that all of the 3-D lighting will be done correctly.
On Wed, Jan 28, 2015 at 11:46:09AM -0500, James Kress wrote:
> If SVG was offered as a "rendering" option, this would not be an issue.
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> -----Original Message-----
> From: owner-vmd-l_at_ks.uiuc.edu [mailto:owner-vmd-l_at_ks.uiuc.edu] On Behalf Of Axel Kohlmeyer
> Sent: Wednesday, January 28, 2015 8:13 AM
> To: M K
> Cc: vmd-l_at_ks.uiuc.edu
> Subject: Re: vmd-l: making self-adjustable high resolution images
> On Wed, Jan 28, 2015 at 5:47 AM, M K <mahyar.karimi20_at_gmail.com> wrote:
> > Hi,
> > When I zoom in an image, I find that atoms find edge and it becomes
> > blurred and ugly. How can I render an image that when I zoom in, it
> > automatically adjusts the resolution and still the atoms remain
> > spherical. What image format it should be and what render machine is able to make it?
> there is no such image format. once you commit something to a given number of pixels, there is no going back. in the same way, you cannot get a higher resolution from your sceen by using a microscope. the only way to get what you want would be to re-render the data on demand, i.e. by using VMD or a raytracing program.
> the next best thing is to render the image at a much higher resolution, i.e. with more pixels (i.e. like using a higher resolution screen in my example above).
> that requires that you use a rendering program, e.g. Tachyon, to generate the image and change the flags that define the resolution of the resulting image.
> > Thanks
> > Mahyar
> Dr. Axel Kohlmeyer akohlmey_at_gmail.com http://goo.gl/1wk0 College of Science & Technology, Temple University, Philadelphia PA, USA International Centre for Theoretical Physics, Trieste. Italy.
-- NIH Center for Macromolecular Modeling and Bioinformatics Beckman Institute for Advanced Science and Technology University of Illinois, 405 N. Mathews Ave, Urbana, IL 61801 http://www.ks.uiuc.edu/~johns/ Phone: 217-244-3349 http://www.ks.uiuc.edu/Research/vmd/