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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  [-rwldngae]  [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

       -d
           List available rules with description then exit
           If a color rule is given, only this rule is listed

       -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, grass,  greens,  grey,  grey.eq,
           grey.log,  grey1.0,  grey255, gyr, haxby, inferno, kelvin, magma, ndvi, ndwi, oranges,
           plasma,    population,    population_dens,     precipitation,     precipitation_daily,
           precipitation_monthly, rainbow, ramp, random, reds, roygbiv, rstcurv, ryb, ryg, sepia,
           slope, soilmoisture, srtm, srtm_plus, terrain, viridis, water, wave
            aspect: aspect oriented grey colors [range: map values]
            aspectcolr: aspect oriented rainbow colors [range: 0 to 360]
            bcyr: blue through cyan through yellow to red [range: map values]
            bgyr: blue through green through yellow to red [range: map values]
            blues: white to blue [range: map values]
            byg: blue through yellow to green [range: map values]
            byr: blue through yellow to red [range: map values]
            celsius: blue to red for degree Celsius temperature [range: -80 to 80]
            corine: EU Corine land cover colors [range: 111 to 995]
            curvature: for terrain curvatures (from v.surf.rst and  r.slope.aspect)  [range:  map
           values]
            differences: differences oriented colors [range: map values]
            elevation:  maps relative ranges of raster values to elevation color ramp [range: map
           values]
            etopo2: colors for ETOPO2 worldwide bathymetry/topography [range: -11000 to 8850]
            evi: enhanced vegetative index colors [range: -1 to 1]
            fahrenheit: blue to red for Fahrenheit temperature [range: -112 to 176]
            gdd: accumulated growing degree days [range: 0 to 6000]
            grass: GRASS GIS green (perceptually uniform) [range: map values]
            greens: white to green [range: map values]
            grey: grey scale [range: map values]
            grey.eq: histogram-equalized grey scale [range: map values]
            grey.log: histogram logarithmic transformed grey scale [range: map values]
            grey1.0: grey scale for raster values between 0.0-1.0 [range: 0 to 1]
            grey255: grey scale for raster values between 0-255 [range: 0 to 255]
            gyr: green through yellow to red [range: map values]
            haxby: relative colors for bathymetry or topography [range: map values]
            inferno: perceptually uniform sequential color table inferno [range: map values]
            kelvin: blue to red for temperature in Kelvin scale [range: 193.15 to 353.15]
            magma: perceptually uniform sequential color table magma [range: map values]
            ndvi: Normalized Difference Vegetation Index colors [range: -1 to 1]
            ndwi: Normalized Difference Water Index colors [range: -200 to 200]
            oranges: white to orange [range: map values]
            plasma: perceptually uniform sequential color table plasma [range: map values]
            population: color table covering human population classification breaks [range: 0  to
           2e+09]
            population_dens:  color table covering human population density classification breaks
           [range: 0 to 1e+09]
            precipitation: precipitation color table (0..2000mm) [range: 0 to 7000]
            precipitation_daily: precipitation color table (0..1000mm) [range: 0 to 10000]
            precipitation_monthly: precipitation color table (0..1000mm) [range: 0 to 1000]
            rainbow: rainbow color table [range: map values]
            ramp: color ramp [range: map values]
            random: random color table [range: map values]
            reds: white to red [range: map values]
            roygbiv:  [range: map values]
            rstcurv: terrain curvature (from r.resamp.rst) [range: map values]
            ryb: red through yellow to blue [range: map values]
            ryg: red through yellow to green [range: map values]
            sepia: yellowish-brown through to white [range: map values]
            slope: r.slope.aspect-type slope colors for raster values 0-90 [range: 0 to 90]
            soilmoisture: soilmoisture color table (0.0-1.0) [range: 0 to 1]
            srtm: color palette for Shuttle Radar Topography Mission elevation [range: -11000  to
           8850]
            srtm_plus:  color  palette  for  Shuttle  Radar  Topography  Mission  elevation (with
           seafloor colors) [range: -11000 to 8850]
            terrain: global elevation color table covering -11000 to  +8850m  [range:  -11000  to
           8850]
            viridis: perceptually uniform sequential color table viridis [range: map values]
            water: water depth [range: map values]
            wave: color wave [range: map values]

       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

       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" (null values) 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

SEE ALSO

        d.colortable, d.histogram, d.legend, r.colors.out r.colors.stddev,  r.support,  r.univar,
       v.colors, v.colors.out, r3.colors, r3.colors.out

       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
       Support for 3D rasters by Soeren Gebbert

       Last changed: $Date: 2018-02-21 11:25:20 +0100 (Wed, 21 Feb 2018) $

SOURCE CODE

       Available at: r.colors source code (history)

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       © 2003-2019 GRASS Development Team, GRASS GIS 7.6.1 Reference Manual