Sophie: GMT-doc-4.5.6-1.fc13 noarch

GMT-doc-4.5.6-1.fc13.noarch.rpm

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">

<!--Converted with LaTeX2HTML 2002-2-1 (1.71)
original version by:  Nikos Drakos, CBLU, University of Leeds
* revised and updated by:  Marcus Hennecke, Ross Moore, Herb Swan
* with significant contributions from:
  Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
<HTML>
<HEAD>
<TITLE>C.2.1 When converting or viewing PostScript goes awry</TITLE>
<META NAME="description" CONTENT="C.2.1 When converting or viewing PostScript goes awry">
<META NAME="keywords" CONTENT="GMT_Docs">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">

<META NAME="Generator" CONTENT="LaTeX2HTML v2002-2-1">
<META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css">

<LINK REL="STYLESHEET" HREF="GMT_Docs.css">

<LINK REL="next" HREF="node194.html">
<LINK REL="previous" HREF="node192.html">
<LINK REL="up" HREF="node192.html">
<LINK REL="next" HREF="node194.html">
</HEAD>

<BODY  bgcolor="#ffffff">
<!--Navigation Panel-->
<A NAME="tex2html5473"
  HREF="node194.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> 
<A NAME="tex2html5467"
  HREF="node192.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> 
<A NAME="tex2html5461"
  HREF="node192.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> 
<A NAME="tex2html5469"
  HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> 
<A NAME="tex2html5471"
  HREF="node258.html">
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.png"></A> 
<BR>
<B> Next:</B> <A NAME="tex2html5474"
  HREF="node194.html">C.2.2 Using ps2raster</A>
<B> Up:</B> <A NAME="tex2html5468"
  HREF="node192.html">C.2 Converting GMT PostScript</A>
<B> Previous:</B> <A NAME="tex2html5462"
  HREF="node192.html">C.2 Converting GMT PostScript</A>
 &nbsp; <B>  <A NAME="tex2html5470"
  HREF="node1.html">Contents</A></B> 
 &nbsp; <B>  <A NAME="tex2html5472"
  HREF="node258.html">Index</A></B> 
<BR>
<BR>
<!--End of Navigation Panel-->

<H2><A NAME="SECTION002021000000000000000"></A>
<A NAME="30728"></A>
<A NAME="30729"></A>
<A NAME="30730"></A>
<BR>
C.2.1 When converting or viewing <I>PostScript</I> goes awry
</H2>
Here are some notorious pitfalls with <I>ghostscript</I><A NAME="30993"></A> (and other rendering programs for that matter).
<DL>
<DT><STRONG>Rendering.</STRONG></DT>
<DD>When you are converting to a raster format, make sure you use a high enough resolution so that the pixels do not show when it is enlarged onto a screen or using a projector. The right choice of resolution depends on the application, but do not feel limited to the default 72 dpi (dots-per-inch) that is offered by most converters.

<P>
</DD>
<DT><STRONG>Image compression.</STRONG></DT>
<DD>There are <I>lossy</I> and <I>non-lossy</I> compressions. A compression algorithm is called ``lossy'' when information is lost in the conversion: there is no way back to get the full original. The effect can be seen when there are sharp color transitions in your image: the edges will get blurry in order to allow a more efficient compression. JPEG uses a lossy compression, PNG is non-lossy, and TIFF generally does not use compression at all. We therefore recommend you convert to PNG if you need to rasterize your plot, and leave JPEG to photographs.

<P>
</DD>
<DT><STRONG>Embedded image compression.</STRONG></DT>
<DD>When your <A NAME="tex2html1776"
  HREF="http://gmt.soest.hawaii.edu"><B>GMT</B></A> plot includes objects produced by <A NAME="tex2html1777"
  HREF="../man/grdimage.html"><I><B>grdimage</B></I></A><A NAME="31000"></A>, <A NAME="tex2html1778"
  HREF="../man/psimage.html"><I><B>psimage</B></I></A><A NAME="31005"></A> or <A NAME="tex2html1779"
  HREF="../man/pslegend.html"><I><B>pslegend</B></I></A><A NAME="31010"></A>, they are seen as ``images''. The default options of <I>ghostscript</I><A NAME="31014"></A> will use a <I>lossy</I> compression (similar to JPEG) on those images when converting them to PDF objects. This can be avoided, however, by inhibiting the compression altogether, or using the non-lossy <I>flate</I> compression, similar to the one used in the old <I>compress</I><A NAME="31017"></A> program. This compression is fully reversible, so that your image does not suffer any loss.

<P>
</DD>
<DT><STRONG>Auto-rotation.</STRONG></DT>
<DD>The <I>ghostscript</I><A NAME="31020"></A> engine has the annoying habit to automatically rotate an image produced with portrait orientation (using the <B>-P</B> option) so that the height is always larger than the width. So if you have an image that was printed in portrait mode but happens to have a width larger than height (for example a global map), it would suddenly get rotated. Again, this function needs to be switched off. Apple's <I>Preview</I><A NAME="31024"></A> uses the <I>ghostscript</I><A NAME="31027"></A> engine and suffers from the same annoying habit. Oddly enough, <I>ghostscript</I><A NAME="31030"></A> does not force landscape plots to be ``horizontal''.

<P>
</DD>
<DT><STRONG>Anti-aliasing.</STRONG></DT>
<DD>This is not something to worry about when converting to PDF, but certainly when producing raster images (discussed below). <I>Anti-aliasing</I> in this context means that the rendering tries to avoid <I>aliasing</I>, for example, sampling only the blacks in a black-and-white hachure. It does so by first oversampling the image and then using ``gray-shades'' when a target pixel is only partially white or black.

<P>
Clearly, this can lead to some unwanted results. First, all edges and lines get blurry and second, the assumption of a white background causes the gray shades to stand out when transferring the image to background with a different color (like the popular sleep-inducing blue in <I>PowerPoint</I><A NAME="31033"></A> presentations). A more surprising effect of anti-aliasing is that the seams between tiles that make up the land mask when using <A NAME="tex2html1780"
  HREF="../man/pscoast.html"><I><B>pscoast</B></I></A><A NAME="31037"></A> will become visible. The anti-aliasing somehow decides to blur the edges of all polygons, even when they are seamlessly connected to other polygons.

<P>
It is therefore wise to overrule the default anti-aliasing option and over-sample the image yourself by choosing a higher resolution.

<P>
</DD>
<DT><STRONG>Including fonts.</STRONG></DT>
<DD>When you are producing print-ready copy to publishers, they will often (and justifiably) ask that you include all fonts in your PDF document. Again, <I>ghostscript</I><A NAME="31041"></A> (and all converters relying on that engine) will not do so by default.
</DD>
</DL>

<P>
<HR>
<!--Navigation Panel-->
<A NAME="tex2html5473"
  HREF="node194.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.png"></A> 
<A NAME="tex2html5467"
  HREF="node192.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.png"></A> 
<A NAME="tex2html5461"
  HREF="node192.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.png"></A> 
<A NAME="tex2html5469"
  HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.png"></A> 
<A NAME="tex2html5471"
  HREF="node258.html">
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.png"></A> 
<BR>
<B> Next:</B> <A NAME="tex2html5474"
  HREF="node194.html">C.2.2 Using ps2raster</A>
<B> Up:</B> <A NAME="tex2html5468"
  HREF="node192.html">C.2 Converting GMT PostScript</A>
<B> Previous:</B> <A NAME="tex2html5462"
  HREF="node192.html">C.2 Converting GMT PostScript</A>
 &nbsp; <B>  <A NAME="tex2html5470"
  HREF="node1.html">Contents</A></B> 
 &nbsp; <B>  <A NAME="tex2html5472"
  HREF="node258.html">Index</A></B> 
<!--End of Navigation Panel-->
<ADDRESS>
Paul Wessel
2011-02-27
</ADDRESS>
</BODY>
</HTML>