<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>GRASS GIS: r.colors</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" href="grassdocs.css" type="text/css">
</head>
<body bgcolor="white">
<img src="grass_logo.png" alt="GRASS logo"><hr align=center size=6 noshade>
<h2>NAME</h2>
<em><b>r.colors</b></em> - Creates/modifies the color table associated with a raster map layer.
<h2>KEYWORDS</h2>
raster, color table
<h2>SYNOPSIS</h2>
<b>r.colors</b><br>
<b>r.colors help</b><br>
<b>r.colors</b> [-<b>rwlngeiq</b>] [<b>map</b>=<em>name</em>] [<b>color</b>=<em>style</em>] [<b>raster</b>=<em>string</em>] [<b>rules</b>=<em>name</em>] [--<b>verbose</b>] [--<b>quiet</b>]
<h3>Flags:</h3>
<DL>
<DT><b>-r</b></DT>
<DD>Remove existing color table</DD>
<DT><b>-w</b></DT>
<DD>Only write new color table if one doesn't already exist</DD>
<DT><b>-l</b></DT>
<DD>List available rules then exit</DD>
<DT><b>-n</b></DT>
<DD>Invert colors</DD>
<DT><b>-g</b></DT>
<DD>Logarithmic scaling</DD>
<DT><b>-e</b></DT>
<DD>Histogram equalization</DD>
<DT><b>-i</b></DT>
<DD>Enter rules interactively</DD>
<DT><b>-q</b></DT>
<DD>Run quietly</DD>
<DT><b>--verbose</b></DT>
<DD>Verbose module output</DD>
<DT><b>--quiet</b></DT>
<DD>Quiet module output</DD>
</DL>
<h3>Parameters:</h3>
<DL>
<DT><b>map</b>=<em>name</em></DT>
<DD>Name of input raster map</DD>
<DT><b>color</b>=<em>style</em></DT>
<DD>Type of color table</DD>
<DD>Options: <em>aspect,aspectcolr,bcyr,bgyr,byg,byr,curvature,differences,elevation,etopo2,evi,grey,grey1.0,grey255,gyr,ndvi,population,rainbow,ramp,ryb,ryg,slope,srtm,terrain,wave,random,grey.eq,grey.log,rules</em></DD>
<DD><b>aspect</b>: aspect oriented grey colors</DD>
<DD><b>aspectcolr</b>: aspect oriented rainbow colors</DD>
<DD><b>bcyr</b>: blue through cyan through yellow to red</DD>
<DD><b>bgyr</b>: blue through green through yellow to red</DD>
<DD><b>byg</b>: blue through yellow to green colors</DD>
<DD><b>byr</b>: blue through yellow to red colors</DD>
<DD><b>curvature</b>: for terrain curvatures (from v.surf.rst and r.slope.aspect curvature colors)</DD>
<DD><b>differences</b>: differences oriented colors</DD>
<DD><b>elevation</b>: maps percentage ranges of raster values to elevation color ramp</DD>
<DD><b>etopo2</b>: rainbow color ramp for the ETOPO2 2-minute Worldwide Bathymetry/Topography dataset</DD>
<DD><b>evi</b>: enhanced vegetative index colors</DD>
<DD><b>grey</b>: grey scale</DD>
<DD><b>grey1.0</b>: grey scale for raster values between 0.0-1.0</DD>
<DD><b>grey255</b>: grey scale for raster values bewtween 0-255</DD>
<DD><b>gyr</b>: green through yellow to red colors</DD>
<DD><b>ndvi</b>: Normalized Difference Vegetation Index colors</DD>
<DD><b>population</b>: color table covering human population classification breaks</DD>
<DD><b>rainbow</b>: rainbow color table</DD>
<DD><b>ramp</b>: color ramp</DD>
<DD><b>ryb</b>: red through yellow to blue colors</DD>
<DD><b>ryg</b>: red through yellow to green colors</DD>
<DD><b>slope</b>: r.slope.aspect-type slope colors for raster values 0-90</DD>
<DD><b>srtm</b>: color palette for Shuttle Radar Topography Mission elevation values</DD>
<DD><b>terrain</b>: global elevation color table covering -11000 to +8850m</DD>
<DD><b>wave</b>: color wave</DD>
<DD><b>random</b>: random color table</DD>
<DD><b>grey.eq</b>: histogram-equalized grey scale</DD>
<DD><b>grey.log</b>: histogram logarithmic transformed grey scale</DD>
<DD><b>rules</b>: create new color table based on user-specified rules</DD>
<DT><b>raster</b>=<em>string</em></DT>
<DD>Raster map name from which to copy color table</DD>
<DT><b>rules</b>=<em>name</em></DT>
<DD>Path to rules file</DD>
</DL>
<h2>DESCRIPTION</h2>
<i>r.colors</i> allows the user to create and/or modify the color table for a
raster map layer. The map layer (specified on the command line by
<b>map=</b><i>name</i>) must exist in the user's current mapset search path.
The color table specified by <b>color=</b><i>type</i> must be one of the
following:
<pre>
color type description
aspect (aspect oriented grey colors)
aspectcolr (aspect oriented rainbow colors)
bcyr (blue through cyan through yellow to red)
bgyr (blue through green through yellow to red)
byg (blue through yellow to green colors)
byr (blue through yellow to red colors)
curvature (for terrain curvatures (from v.surf.rst and r.slope.aspect curvature colors))
differences (differences oriented colors)
elevation (maps percentage ranges of raster values to elevation color ramp)
etopo2 (rainbow color ramp for the ETOPO2 2-minute Worldwide Bathymetry/Topography dataset)
evi (enhanced vegetative index colors)
grey (grey scale)
grey1.0 (grey scale for raster values between 0.0-1.0)
grey255 (grey scale for raster values bewtween 0-255)
grey.eq (histogram-equalized grey scale)
grey.log (histogram logarithmic transformed grey scale)
gyr (green through yellow to red colors)
ndvi (Normalized Difference Vegetation Index colors)
population (color table covering human population classification breaks)
rainbow (rainbow color table)
ramp (color ramp)
random (random color table)
rules (create new color table based on user-specified rules)
ryb (red through yellow to blue colors)
ryg (red through yellow to green colors)
slope (r.slope.aspect-type slope colors for raster values 0-90)
srtm (color palette for Shuttle Radar Topography Mission elevation values)
terrain (global elevation color table covering -11000 to +8850m)
wave (color wave)
</pre>
<p>
The <b>rast</b> option allows user to specify a raster map <i>name</i> from which
to copy the color map.
<p>
Extra color tables (aspect, aspectcolr, bcyr, bgyr, byg, byr, curvature, differences,
elevation, etopo2, evi, grey, grey1.0, grey255, gyr, ndvi, population, rainbow, ramp, ryb, ryg, slope, srtm, terrain, wave) are stored in $GISBASE/etc/colors/.
User-defined color tables can also be stored in this directory for access from the <em>color</em> parameter.
<p>
The <b>-e</b> flag equalizes the original raster's color table. It can preclude
the need for <em>grey.eq</em> rule, when used as
<b>-e color=</b><em>grey</em>. Note however, that this will not yield a color
table identical to <em>color=grey.eq</em>, because <em>grey.eq</em> scales
the fraction by 256 to get a grey level, while <b>-e</b> uses it to interpolate
the original colour table. If the original colour table is a 0-255 grey scale,
<b>-e</b> is effectively scaling the fraction by 255. Different algorithms are
used. <b>-e</b> is designed to work with any color table, both the floating
point and the integer raster maps.
<p>
The <b>-g</b> flag divides the raster's grey value range into 100
logarithmically equal steps (where "step" is a rule with the same grey level
for the start and end points). It can preclude the need for <em>grey.log</em>
rule, when used as <b>-g color=</b><em>grey</em>. Note however, that this
will not yield a color table identical to <em>color=grey.log</em>. Different
algorithms are used. Unlike <b>color=</b><em>grey.log</em>, <b>-g</b> is
designed to work with both floating point and integer rasters, without
performance issues with large datasets, of any original color table. Logarithmic
scaling doesn't work on negative values. In the case when the value range
includes zero, there's no realistic solution.
<p>
The <b>-e</b> and <b>-g</b> flags are not mutually exclusive.
<p>
If the user specifies the <b>-w</b> flag, the current color table file for
the input map will not be overwritten. This means that the color table is
created only if the <i>map</i> does not already have a color table. If this
option is not specified, the color table will be created if one does not
exist, or modified if it does.
<p>
If the user sets the <b>-q</b> flag, <i>r.colors</i> will run quietly,
Without printing numerous messages on its progress to standard output.
<p>Color table types <i>aspect, grey, grey.eq</i> (histogram-equalized grey
scale), <i>byg</i> (blue-yellow-green), <i>byr</i> (blue-yellow-red),
<i>gyr</i> (green-yellow-red), <i>rainbow, ramp, ryg</i> (red-yellow-green),
<i>random</i>, and <i>wave</i> are pre-defined color tables that
<i>r.colors</i> knows how to create without any further input.
<p>
In general, tables which associate colors with percentages (aspect, bcyr, byg,
byr, elevation, grey, gyr, rainbow, ramp, ryb, ryg and wave) can be applied to
any data, while those which use absolute values (aspectcolr, curvature, etopo2,
evi, ndvi, population, slope, srtm, and terrain) only make sense for data with
certain ranges.
One can get a rough idea of the applicability of a colour table by reading the
corresponding rules file ($GISBASE/etc/colors/<name>).
For example the <em>slope</em> rule is defined as:
<div class="code"><pre>
0 255:255:255
2 255:255:0
5 0:255:0
10 0:255 255
15 0:0:255
30 255:0:255
50 255:0:0
90 0:0:0
</pre></div>
<p>
This is designed for the slope map generated by r.slope.aspect, where the value
is a slope angle between 0 and 90 degrees.
<p>
Similarly, the <em>aspectcolr</em> rule:
<div class="code"><pre>
0 white
1 yellow
90 green
180 cyan
270 red
360 yellow
</pre></div>
<p>
is designed for the aspect maps produced by r.slope.aspect, where the value is a
heading between 0 and 360 degrees.
<p>
The <i>rules</i> color table type will cause <i>r.colors</i> to read color
table specifications from standard input (stdin) and will build the color table
accordingly.
<p>
Using color table type <i>rules</i>, there are <!--three-->two ways to build a color
table: <!--by color list,--> by category values and by "percent" values.
<!-- HB: this causes an error in current code, maybe easy to enable functionality from old code??
<p>
Building a customized color table by color list is the simplest of the three
rules methods: just list the colors you wish to appear in the color table in the
order that you wish them to appear. Use the standard GRASS color names: white,
black, red, green, blue, yellow, magenta, cyan, aqua, grey, gray, orange, brown,
purple, violet, and indigo.
<p>
For example, to create a color table for the raster map layer <i>elevation</i>
that assigns greens to low map category values, browns to the next larger
map category values, and yellows to the still larger map category values,
one would type:
<div class="code"><pre>
<b>r.colors map=</b><i>elevation</i> <b>color=</b><i>rules</i>
green
brown
yellow
end
</pre></div>
-->
<p>
To build a color table by category values' indices, the user should determine
the range of category values in the raster map layer with which the color table
will be used. Specific category values will then be associated with specific
colors. Note that a color does not have to be assigned for every valid category
value because <i>r.colors</i> will interpolate a color ramp to fill in where
color specification rules have been left out. The format of such a specification
is as follows:
<div class="code"><pre>
category_value color_name
category_value color_name
.. ..
.. ..
category_value color_name
end
</pre></div>
<p>
Each category value must be valid for the raster map layer, category values must
be in ascending order and only use standard GRASS color names (see above).
<p>
Colors can also be specified by color numbers each in the range 0-255. The
format of a category value color table specification using color numbers instead
of color names is as follows:
<div class="code"><pre>
category_value red_number:green_number:blue_number
category_value red_number:green_number:blue_number
.. .. .. ..
.. .. .. ..
category_value red_number:green_number:blue_number
end
</pre></div>
<p>
Specifying a color table by "percent" values allows one to treat a color table
as if it were numbered from 0 to 100. The format of a "percent" value color
table specification is the same as for a category value color specification,
except that the category values are replaced by "percent" values, each from
0-100, in ascending order. The format is as follows:
<div class="code"><pre>
percent_value% color_name
percent_value% color_name
.. ..
.. ..
percent_value% color_name
end
</pre></div>
<p>
Using "percent" value color table specification rules, colors can also
be specified by color numbers each in the range 0-255. The format of a
percent value color table specification using color numbers instead of
color names is as follows:
<div class="code"><pre>
percent_value% red_number:green_number:blue_number
percent_value% red_number:green_number:blue_number
.. .. .. ..
.. .. .. ..
percent_value% red_number:green_number:blue_number
end
</pre></div>
<p>
Note that you can also mix these <!--three-->two methods of color table
specification; for example:
<div class="code"><pre>
0 black
10% yellow
78 blue<!--\n magenta
purple
brown-->
100% 0:255:230
end
</pre></div>
<p>
To set the NULL (no data) color, use the "nv" parameter:
<div class="code"><pre>
0 black
10% yellow
nv white
end
</pre></div>
<h2>EXAMPLES</h2>
The below example shows how you can specify colors for a three category map,
assigning red to category 1, green to category 2, and blue to category 3. Start
by using a text editor to create the following rules specification file (save it
with the name <i>rules.file</i>):
<div class="code"><pre>
1 red
2 green
3 blue
end
</pre></div>
<p>
The color table can then by assigned to map <i>threecats</i> by the following
GRASS command:
<div class="code"><pre>
cat rules.file | r.colors map=threecats color=rules
</pre></div>
<P><BR>
To create a natural looking LUT for true map layer <i>elevation</i>, use the
following rules specification file. It will assign light green shades to the
lower elevations (first 20% of the LUT), and then darker greens (next 15%, and
next 20%) and light browns (next 20%) for middle elevations, and darker browns
(next 15%) for higher elevations, and finally yellow for the highest peaks (last
10% of LUT).
<div class="code"><pre>
0% 0:230:0
20% 0:160:0
35% 50:130:0
55% 120:100:30
75% 120:130:40
90% 170:160:50
100% 255:255:100
</pre></div>
<h2>SEE ALSO</h2>
<em>
<a href="d.colors.html">d.colors</a>,
<a href="d.colortable.html">d.colortable</a>,
<a href="d.legend.html">d.legend</a>,
<a href="r.support.html">r.support</a>
</em>
<p>
<a href="http://colorbrewer.org">ColorBrewer</a> is an online tool designed to
help people select good color schemes for maps and other graphics.
<h2>AUTHORS</h2>
Michael Shapiro and David Johnson
<p>
<i>Last changed: $Date: 2008-02-24 12:16:04 +0100 (Sun, 24 Feb 2008) $</i>
<HR>
<P><a href="index.html">Main index</a> - <a href="raster.html">raster index</a> - <a href="full_index.html">Full index</a></P>
<P>© 2003-2008 <a href="http://grass.osgeo.org">GRASS Development Team</a></p>
</body>
</html>
