undesired grid in ps/eps outputs generated by filled.contour or image

On Fri, 6 Feb 2009, Marc Schwartz wrote:

on 02/06/2009 01:32 PM Rachel Albrecht wrote:

Hi!

Whenever I save a graphic in ps/eps format generated by
filled.contour or image, an undesired grid is added to it (not
visible on the X11 screen). For example:

postscript("volcano.eps")
filled.contour(volcano,col=gray(seq(0,1,,50)),levels=seq(min(volcano),max(volcano),,50))

dev.off()

Any ideia how to eliminate this grid?

Thanks,
Rachel

I can confirm the problem, running:

 R version 2.8.1 Patched (2009-01-24 r47726)

on Fedora 10.

The problem is actually worse if using the pdf() device, with additional
artifacts present.

There was a posting about this back in 2003:

 https://stat.ethz.ch/pipermail/r-help/2003-August/037348.html

with no replies. There is a bug report here from 2004:

 http://bugs.r-project.org/cgi-bin/R/Graphics?id=6763

that seems to be related. So it seems the issue has been around for a
while.

I tried increasing the granularity of the color scale, though without
any benefit.

Will have to defer to the graphics device wizaRds on this one.

Marc Schwartz

Thanks to Prof. Ripley for pointing out my error here and my apologies
for leaving the impression that this was related to the R graphics devices.

As it turns out, this is uniquely a PS/PDF viewer issue related to the
use of anti-aliasing in the viewer.

I had initially used Evince, which is the default PS/PDF viewer in GNOME
(Linux desktop environment). In Evince, there does not appear to be an
option to disable anti-aliasing, either within the application or in
GConf, which is another application to configure GNOME application
related settings.

When using Adobe's Acrobat Reader for the PDF file, if I go into Edit ->
Preferences -> Page Display and disable "Smooth line art", the lines do
indeed go away. There are two other anti-aliasing settings there,
"Smooth Text" and "Smooth images", which do not appear to have any
effect here.

I installed gsview, which is no longer part of the default Ghostscript
installation for Fedora (it is now part of the new RPMFusion repo).

In gsview, if I go into Media -> Display Settings and change "Graphics
Alpha" from 4 bits to 1 bit (to disable anti-aliasing), the image
displays properly. The "Text Alpha" setting does not appear to affect this.

So, to reiterate, this is a PS/PDF viewer application problem and not an
R graphics device issue. If you are unable to disable anti-aliasing in
the viewer that you are using, try another application.

Regards,

Marc