Re: Re: vertical lines through maps , Re: ncl-talk posting

From: Jonathan Vigh <vigh_at_nyahnyahspammersnyahnyah>
Date: Sun, 11 Dec 2005 12:37:17 -0700

Hi Micah,
    This sounds like a problem I had last year - thin lines or stippling
which shows up in gv (depending on whether antialiasing is turned on),
but if you print from the postscript, everything is fine. If you convert
to gif or png, the lines still show up.

Mark Stevens sent a reply which explains what is going on. I've copied
this here (see ncl-talk acrhives April 23-24, 2004 for the original

This is a problem I looked into before. The problem isn't in the
postscript plot, it arises when viewing the postscript plot or
converting it to another format. You can see this by using gv. Start gv
with the postscript file. At the top of gv there is a menu button
labeled "State". Click on the item labeled "Antialias" to turn it on or
off. With the antialias turned on the problem will be there, with the
antialias turned off the problem will go away. If you use gs I think by
default the antialiasing is off so the problem doesn't appear, but there
are options to turn it on or off.

When you use "convert" the antialiasing is by default used so the
problem is visible. You can turn it off with the +antialias option.

The real problem is that when the antialiasing is turned off the plot
area will be fine but the fonts will look really bad. Also sometimes
this problem appears and other times it doesn't. When I run scripts
sometimes I get this problem in one plot, but not in another.


So if you indeed want clean gif or png (say for web applications), I
recommend using ghostscript instead of convert for the ps->png
conversion. There are some pesky options to set to get a nice optimized
gif or png, but I've been happy with it, and I think it takes care of
this problem. My sysadmin wrote a nifty little script to do this, but I
should probably ask him first before distributing it to the masses. If
he say's okay, I'll try to remember to send it out tomorrow.

Jonathan Vigh

On Sun, 2005-12-11 at 10:29, Micah Sklut wrote:
> Regarding the vertical transparent lines:
> I just discovered something interesting regarding the vertical lines
> on the ps files:
> When viewing the ps file on one monitor using GGV (gnome ghostview
> 1.99)
> then vertical lines are present.
> Viewing the file on another monitor using a different ghostview view
> (gv 3.5.8), the lines
> are NOT present.
> When, converting to gif (using Image Magick- convert tool), the lines
> are present regardless...
> This leads me to believe the lines are not just a result of the
> convert program, but are being derived from the original file.
> Any thoughts on this?
> Micah
> On 12/11/05, Micah Sklut <> wrote:
> Hi Mary, (original email - not sent to ncl-talk below)
> The transparent vertical lines are appearing on my original
> postscript files:
> After recieving the previous email from Dennis, I thought this
> issue might
> be due to how I'm defining my coordinates, but no luck so
> far...
> Here's the data file if you would like to run the script:
> Thanks.
> Micah
> Original email:
> > Hi,
> >
> > I am getting thin transparent vertical lines through my
> maps.
> > Is anyone aware of why this is and if it is avoidable?
> >
> > Here is an example:
> >
> >
> > In this image there is one vertical line that goes through
> the ocean
> > along the prime
> > meridian, and several vertical lines along the continents to
> the west.
> >
> > code:
> >
> >
> > Thanks.
> >
> > Micah
> On 12/10/05, Mary Haley <> wrote:
> Micah,
> This is just to let you know that you posted this
> question from your
> email address, but you are
> subscribed under a
> different address on ncl-talk, so the posting didn't
> go through. I
> went ahead and added this email address as a valid one
> to post from.
> Meanwhile, with regard to your question, are these
> vertical lines
> appearing in your original PostScript file? If not,
> then it's possible
> that the tool you are using to convert from PS to GIF
> is introducing
> the lines.
> Can you send us the original PS file so we can look
> into this?
> Thanks,
> --Mary
> ______________________________________________________________________
> _______________________________________________
> ncl-talk mailing list

Jonathan Vigh, Ph.D. Candidate              work phone: 970.491.8988                         
Department of Atmospheric Science 
Colorado State University
ncl-talk mailing list
Received on Sun Dec 11 2005 - 12:37:17 MST

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