r.colors(1grass)

Grass User's Manual

r.colors(1grass)

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

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

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

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

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

AUTHORS¶

Michael Shapiro and David Johnson

Last changed: $Date: 2011-01-03 14:53:58 +0100 (Mon, 03 Jan 2011) $

Full index

GRASS 6.4.2

Source file:	r.colors.1grass.en.gz (from grass-doc 6.4.2-2)
Source last updated:	2012-06-06T14:04:01Z
Converted to HTML:	2017-06-07T16:52:51Z