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<H1><A NAME="SECTION0012150000000000000000">
4.15 Color palette tables</A>
</H1>
<P>
<A NAME="4335"></A>
<A NAME="4336"></A>
<P>
Several programs, such as those which read 2-D gridded data sets and create
colored images or shaded reliefs, need to be told what colors to use and
over what <I>z</I>-range each color applies. This is the purpose of the
color palette table (cpt-file). These files may also be used by <A NAME="tex2html256"
HREF="../psxy.html"><I><B>psxy</B></I></A><A NAME="4827"></A>
and <A NAME="tex2html257"
HREF="../psxyz.html"><I><B>psxyz</B></I></A><A NAME="4836"></A> to plot color-filled symbols.
The colors may be specified either in the RGB (red, green, blue) system or
in the HSV system (hue, saturation, value),
and the parameter COLOR_MODEL in the <U>.gmtdefaults</U> file must
be set accordingly. Using the RGB system, the format of the cpt-file is:
<P>
<DIV ALIGN="CENTER">
<TABLE CELLPADDING=3>
<TR><TD ALIGN="LEFT">z<IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img37.gif"
ALT="$_0$"></TD>
<TD ALIGN="LEFT">R<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"></TD>
<TD ALIGN="LEFT">G<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"></TD>
<TD ALIGN="LEFT">B<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"></TD>
<TD ALIGN="LEFT">z<IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img13.gif"
ALT="$_1$"></TD>
<TD ALIGN="LEFT">R<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$"></TD>
<TD ALIGN="LEFT">G<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$"></TD>
<TD ALIGN="LEFT">B<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$"></TD>
<TD ALIGN="LEFT">[<B>A</B>]</TD>
</TR>
<TR><TD ALIGN="LEFT">...</TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">z<IMG
WIDTH="26" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img40.gif"
ALT="$_{n-2}$"></TD>
<TD ALIGN="LEFT">R<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"></TD>
<TD ALIGN="LEFT">G<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"></TD>
<TD ALIGN="LEFT">B<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"></TD>
<TD ALIGN="LEFT">z<IMG
WIDTH="26" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img41.gif"
ALT="$_{n-1}$"></TD>
<TD ALIGN="LEFT">R<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$"></TD>
<TD ALIGN="LEFT">G<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$"></TD>
<TD ALIGN="LEFT">B<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$"></TD>
<TD ALIGN="LEFT">[<B>A</B>]</TD>
</TR>
</TABLE>
</DIV>
<P>
Thus, for each ``<I>z</I>-slice'', defined as the interval between two boundaries
(e.g., <I>z<IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img37.gif"
ALT="$_0$"></I> to <I>z<IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img13.gif"
ALT="$_1$"></I>), the color can be constant (by letting R<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$">
= R<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$">, G<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"> = G<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$">, and B<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img38.gif"
ALT="$_{min}$"> = B<IMG
WIDTH="25" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img39.gif"
ALT="$_{max}$">) or a continuous,
linear function of <I>z</I>. The optional flag <B>A</B> is used to indicate anotation
of the colorscale when plotted using <A NAME="tex2html258"
HREF="../psscale.html"><I><B>psscale</B></I></A><A NAME="4846"></A>. <B>A</B> may be <B>L</B>,
<B>U</B>, or <B>B</B> to select anotation of the lower, upper, or both limits
of the particular <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-slice. However, the standard <B>-B</B> option can be used
by <A NAME="tex2html259"
HREF="../psscale.html"><I><B>psscale</B></I></A><A NAME="4856"></A> to affect anotation and ticking of colorscales. The
background color (for <I>z</I>-values <IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img42.gif"
ALT="$<$"> <I>z<IMG
WIDTH="11" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img37.gif"
ALT="$_0$"></I>), foreground color
(for <I>z</I>-values <IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img36.gif"
ALT="$>$"> <I>z<IMG
WIDTH="26" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img41.gif"
ALT="$_{n-1}$"></I>), and not-a-number (NaN) color (for
<I>z</I>-values = NaN) are all defined in the <U>.gmtdefaults</U>
file, but can be overridden by the statements
<P>
<DIV ALIGN="CENTER">
<TABLE CELLPADDING=3>
<TR><TD ALIGN="LEFT">B</TD>
<TD ALIGN="LEFT">R<IMG
WIDTH="27" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img43.gif"
ALT="$_{back}$"></TD>
<TD ALIGN="LEFT">G<IMG
WIDTH="27" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img43.gif"
ALT="$_{back}$"></TD>
<TD ALIGN="LEFT">B<IMG
WIDTH="27" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img43.gif"
ALT="$_{back}$"></TD>
</TR>
<TR><TD ALIGN="LEFT">F</TD>
<TD ALIGN="LEFT">R<IMG
WIDTH="27" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img44.gif"
ALT="$_{fore}$"></TD>
<TD ALIGN="LEFT">G<IMG
WIDTH="27" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img44.gif"
ALT="$_{fore}$"></TD>
<TD ALIGN="LEFT">B<IMG
WIDTH="27" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img44.gif"
ALT="$_{fore}$"></TD>
</TR>
<TR><TD ALIGN="LEFT">N</TD>
<TD ALIGN="LEFT">R<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img45.gif"
ALT="$_{nan}$"></TD>
<TD ALIGN="LEFT">G<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img45.gif"
ALT="$_{nan}$"></TD>
<TD ALIGN="LEFT">B<IMG
WIDTH="23" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img45.gif"
ALT="$_{nan}$"></TD>
</TR>
</TABLE>
</DIV>
<P>
which can be inserted into the beginning or end of the cpt-file. If
you prefer the HSV system, set the
<U>.gmtdefaults</U> parameter accordingly and replace red, green,
blue with hue, saturation, value. Color palette tables that contain
grayshades only may replace the r-g-b triplets with a single grayshade
in the 0-255 range.
<P>
A few programs (i.e., those that plot polygons such as <A NAME="tex2html260"
HREF="../grdview.html"><I><B>grdview</B></I></A><A NAME="4867"></A>,
<A NAME="tex2html261"
HREF="../psscale.html"><I><B>psscale</B></I></A><A NAME="4876"></A>, and <A NAME="tex2html262"
HREF="../psxy.html"><I><B>psxy</B></I></A><A NAME="4885"></A>) can accept pattern fills instead
of grayshades. You must give the pattern as in the previous section (no
leading <B>-G</B> of course), and only the first (low <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">) is used (we cannot
interpolate between patterns).
Finally, some programs let you skip features
whose <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">-slice in the cptfile has grayshades set to -. As an example,
consider
<P>
<DIV ALIGN="CENTER">
<TABLE CELLPADDING=3>
<TR><TD ALIGN="LEFT">30</TD>
<TD ALIGN="LEFT">p200/16</TD>
<TD ALIGN="LEFT">80</TD>
<TD ALIGN="LEFT">-</TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">80</TD>
<TD ALIGN="LEFT">-</TD>
<TD ALIGN="LEFT">100</TD>
<TD ALIGN="LEFT">-</TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
<TD ALIGN="LEFT"> </TD>
</TR>
<TR><TD ALIGN="LEFT">100</TD>
<TD ALIGN="LEFT">255</TD>
<TD ALIGN="LEFT">0</TD>
<TD ALIGN="LEFT">0</TD>
<TD ALIGN="LEFT">200</TD>
<TD ALIGN="LEFT">255</TD>
<TD ALIGN="LEFT">255</TD>
<TD ALIGN="LEFT">0</TD>
<TD ALIGN="LEFT"> </TD>
</TR>
</TABLE>
</DIV>
<P>
where slice <IMG
WIDTH="81" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img46.gif"
ALT="$30 < z < 80$"> is painted with pattern # 16 at 200 dpi,
slice <IMG
WIDTH="89" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img47.gif"
ALT="$80 < z < 100$"> is skipped, while slice <IMG
WIDTH="97" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img48.gif"
ALT="$100 < z < 200$"> is
painted in a range of red to yellow, depending on the actual value
of <IMG
WIDTH="10" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img17.gif"
ALT="$z$">.
<P>
<A NAME="4410"></A>
<A NAME="4411"></A>
<P>
<A NAME="4412"></A>
<A NAME="4413"></A>
<A NAME="4414"></A>
<A NAME="4415"></A>
<P>
Some programs like <A NAME="tex2html263"
HREF="../grdimage.html"><I><B>grdimage</B></I></A><A NAME="4895"></A> and <A NAME="tex2html264"
HREF="../grdview.html"><I><B>grdview</B></I></A><A NAME="4904"></A> apply artificial
illumination to achieve shaded relief maps. This is typically done
by finding the directional gradient in the direction of the artificial
light source and scaling the gradients to have approximately a normal
distribution on the interval <IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img42.gif"
ALT="$<$">-1,+1<IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img36.gif"
ALT="$>$">. These intensities are used
to add ``white'' or ``black'' to the color as defined by the <I>z</I>-values
and the cpt-file. An intensity of zero leaves the color unchanged.
Higher values will brighten the color, lower values will darken it,
all without changing the original hue of the color (see Appendix I
for more details). The illumination is decoupled from the data
grd-file in that a separate grdfile holding intensities in the
<IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img42.gif"
ALT="$<$">-1,+1<IMG
WIDTH="16" HEIGHT="29" ALIGN="MIDDLE" BORDER="0"
SRC="img36.gif"
ALT="$>$"> range must be provided. Such intensity files can be
derived from the data grdfile using <A NAME="tex2html265"
HREF="../grdgradient.html"><I><B>grdgradient</B></I></A><A NAME="4913"></A> and modified
with <A NAME="tex2html266"
HREF="../grdhisteq.html"><I><B>grdhisteq</B></I></A><A NAME="4922"></A>, but could equally well be a separate data set.
E.g., some side-scan sonar systems collect both bathymetry and
backscatter intensities, and one may want to use the latter information
to specify the illumination of the colors defined by the former.
Similarly, one could portray magnetic anomalies superimposed on
topography by using the former for colors and the latter for shading.
<P>
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<ADDRESS>
Paul Wessel
2001-04-18
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