GRASS GIS manual: r.colors

Note: A new GRASS GIS stable version has been released: GRASS GIS 7.4, available here.
Updated manual page: here

NAME

r.colors - Creates/modifies the color table associated with a raster map.

KEYWORDS

raster, color table

SYNOPSIS

r.colors

r.colors --help

r.colors [-rwlngae] [map=name[,name,...]] [file=name] [color=style] [raster=name] [raster_3d=name] [rules=name] [--help] [--verbose] [--quiet] [--ui]

Flags:

-r: Remove existing color table
-w: Only write new color table if it does not already exist
-l: List available rules then exit
-n: Invert colors
-g: Logarithmic scaling
-a: Logarithmic-absolute scaling
-e: Histogram equalization
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

map=name[,name,...]: Name of raster map(s)
file=name: Input file with one map name per line; Input map names can be defined in an input file in case a large amount of maps must be specified. This option is mutual exclusive to the map option.
color=style: Name of color table; Options: aspect, aspectcolr, bcyr, bgyr, blues, byg, byr, celsius, corine, curvature, differences, elevation, etopo2, evi, fahrenheit, gdd, greens, grey, grey.eq, grey.log, grey1.0, grey255, gyr, haxby, kelvin, ndvi, ndwi, oranges, population, population_dens, precipitation, precipitation_daily, precipitation_monthly, rainbow, ramp, random, reds, rstcurv, ryb, ryg, sepia, slope, srtm, srtm_plus, 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; blues: white to blue; 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; fahrenheit: blue to red for Fahrenheit temperature; gdd: accumulated growing degree days; greens: white to green; 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; kelvin: blue to red for temperature in Kelvin scale; ndvi: Normalized Difference Vegetation Index colors; ndwi: Normalized Difference Water Index colors; oranges: white to orange; 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_daily: precipitation color table (0..1000mm); precipitation_monthly: precipitation color table (0..1000mm); rainbow: rainbow color table; ramp: color ramp; random: random color table; reds: white to red; rstcurv: terrain curvature (from r.resamp.rst); 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; srtm_plus: color palette for Shuttle Radar Topography Mission elevation (with seafloor colors); terrain: global elevation color table covering -11000 to +8850m; wave: color wave
raster=name: Raster map from which to copy color table
raster_3d=name: 3D raster map from which to copy color table
rules=name: Path to rules file; "-" to read rules from stdin

DESCRIPTION
NOTES
EXAMPLES
SEE ALSO
AUTHORS

DESCRIPTION

r.colors allows the user to create and/or modify the color table for a raster map or several raster maps at once. The raster maps (specified on the command line by map or as file using an input file with one map name per line) must exist in the user's current mapset search path.

The raster option allows user to specify a raster map name from which to copy the color map.

The raster_3d option allows user to specify a 3D raster map name from which to copy the color map.

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 color table. If the original color 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.

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 case several input raster maps are provided the range (min, max) of all maps will be used for color table creation. Hence the created color table will span from the smallest minimum to the largest maximum value of all input raster maps and will be applied to all input raster maps.

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 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 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, 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

NOTES

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 or in a user defined directory. See also r.colors.out for printing color tables easily to the terminal.

The color table assigned to a raster map is stored in $GISDBASE/location/mapset/colr/.

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 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 map=current_raster -n rast=current_raster

AUTHORS

Michael Shapiro and David Johnson
Support for 3D rasters by Soeren Gebbert

Last changed: $Date: 2014-12-24 02:56:44 -0800 (Wed, 24 Dec 2014) $

SOURCE CODE

Available at: r.colors source code (history)