Provided by: grass-doc_6.4.3-3_all 
NAME
r.colors - Creates/modifies the color table associated with a raster map layer.
KEYWORDS
raster, color table
SYNOPSIS
r.colors
r.colors help
r.colors [-rwlngaeiq] [map=name] [color=style] [raster=string] [rules=name] [--verbose]
[--quiet]
Flags:
-r
Remove existing color table
-w
Only write new color table if one doesn't already exist
-l
List available rules then exit
-n
Invert colors
-g
Logarithmic scaling
-a
Logarithmic-absolute scaling
-e
Histogram equalization
-i
Enter rules interactively
-q
Run quietly
--verbose
Verbose module output
--quiet
Quiet module output
Parameters:
map=name
Name of input raster map
color=style
Type of color table
Options:
aspect,aspectcolr,bcyr,bgyr,byg,byr,celsius,corine,curvature,differences,elevation,etopo2,evi,gdd,grey,grey.eq,grey.log,grey1.0,grey255,gyr,haxby,ndvi,population,population_dens,precipitation,precipitation_monthly,rainbow,ramp,random,rstcurv,rules,ryb,ryg,sepia,slope,srtm,terrain,wave
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
byr: blue through yellow to red
celsius: blue to red for degree Celsius temperature
corine: EU Corine land cover colors
curvature: for terrain curvatures (from v.surf.rst and r.slope.aspect)
differences: differences oriented colors
elevation: maps relative ranges of raster values to elevation color ramp
etopo2: colors for ETOPO2 worldwide bathymetry/topography
evi: enhanced vegetative index colors
gdd: accumulated growing degree days
grey: grey scale
grey.eq: histogram-equalized grey scale
grey.log: histogram logarithmic transformed grey scale
grey1.0: grey scale for raster values between 0.0-1.0
grey255: grey scale for raster values between 0-255
gyr: green through yellow to red
haxby: relative colors for bathymetry or topography
ndvi: Normalized Difference Vegetation Index colors
population: color table covering human population classification breaks
population_dens: color table covering human population density classification breaks
precipitation: precipitation color table (0..2000mm)
precipitation_monthly: precipitation color table (0..1000mm)
rainbow: rainbow color table
ramp: color ramp
random: random color table
rstcurv: terrain curvature (from r.resamp.rst)
rules: create new color table based on user-specified rules read from stdin
ryb: red through yellow to blue
ryg: red through yellow to green
sepia: yellowish-brown through to white
slope: r.slope.aspect-type slope colors for raster values 0-90
srtm: color palette for Shuttle Radar Topography Mission elevation
terrain: global elevation color table covering -11000 to +8850m
wave: color wave
raster=string
Raster map name from which to copy color table
rules=name
Path to rules file ("-" to read rules from stdin)
DESCRIPTION
r.colors 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 map=name) must exist in the user's current mapset search path.
The rast option allows user to specify a raster map name from which to copy the color map.
All color tables are stored in $GISBASE/etc/colors/. Further user-defined color tables can also be stored
in this directory for access from the color parameter.
The -e flag equalizes the original raster's color table. It can preclude the need for grey.eq rule, when
used as -e color=grey. Note however, that this will not yield a color table identical to color=grey.eq,
because grey.eq scales the fraction by 256 to get a grey level, while -e uses it to interpolate the
original colour table. If the original colour table is a 0-255 grey scale, -e is effectively scaling the
fraction by 255. Different algorithms are used. -e is designed to work with any color table, both the
floating point and the integer raster maps.
The -g 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 grey.log rule,
when used as -g color=grey. Note however, that this will not yield a color table identical to
color=grey.log. Different algorithms are used. Unlike color=grey.log, -g 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.
The -e and -g flags are not mutually exclusive.
If the user specifies the -w 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 map 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.
If the user sets the -q flag, r.colors will run quietly, Without printing numerous messages on its
progress to standard output.
Color table types aspect, grey, grey.eq (histogram-equalized grey scale), byg (blue-yellow-green), byr
(blue-yellow-red), gyr (green-yellow-red), rainbow, ramp, ryg (red-yellow-green), random, and wave are
pre-defined color tables that r.colors knows how to create without any further input.
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/). For example the slope rule is defined as:
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
This is designed for the slope map generated by r.slope.aspect, where the value is a slope angle between
0 and 90 degrees.
Similarly, the aspectcolr rule:
0 white
1 yellow
90 green
180 cyan
270 red
360 yellow
is designed for the aspect maps produced by r.slope.aspect, where the value is a heading between 0 and
360 degrees.
The rules color table type will cause r.colors to read color table specifications from standard input
(stdin) and will build the color table accordingly.
Using color table type rules, there are two ways to build a color table: by category values and by
"percent" values.
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 r.colors 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:
category_value color_name
category_value color_name
category_value color_name
end
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 (aqua, black, blue, brown, cyan, gray, green, grey, indigo,
magenta, orange, purple, red, violet, white, yellow).
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:
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
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:
percent_value% color_name
percent_value% color_name
percent_value% color_name
end
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:
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
Note that you can also mix these two methods of color table specification; for example:
0 black
10% yellow
78 blue
100% 0:255:230
end
To set the NULL (no data) color, use the "nv" parameter:
0 black
10% yellow
nv white
end
To set the color to used for undefined values (beyond the range of the color rules) use the "default"
parameter:
0 red
1 blue
default grey
end
EXAMPLES
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 rules.file):
1 red
2 green
3 blue
end
The color table can then by assigned to map threecats by the following GRASS commands (two ways are
available):
# read input from stdin
cat rules.file | r.colors map=threecats color=rules
# read directly from file
r.colors map=threecats rules=rules.file
To create a natural looking lookup table (LUT) for true map layer elevation, 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).
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
To invert the current rules:
r.colors current_raster -n rast=current_raster
SEE ALSO
d.colors, d.colortable, d.histogram, d.legend, r.colors.stddev, r.support, r.univar, v.colors
See also wiki page Color tables (from GRASS User Wiki)
ColorBrewer is an online tool designed to help people select good color schemes for maps and other
graphics.
AUTHORS
Michael Shapiro and David Johnson
Last changed: $Date: 2013-02-15 14:04:18 -0800 (Fri, 15 Feb 2013) $
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© 2003-2013 GRASS Development Team
GRASS 6.4.3 r.colors(1grass)