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


       raster, color table


       r.colors help
       r.colors   [-rwlngaeiq]    [map=name]     [color=style]    [raster=string]    [rules=name]
       [--verbose]  [--quiet]

           Remove existing color table

           Only write new color table if one doesn't already exist

           List available rules then exit

           Invert colors

           Logarithmic scaling

           Logarithmic-absolute scaling

           Histogram equalization

           Enter rules interactively

           Run quietly

           Verbose module output

           Quiet module output

           Name of input raster map

           Type of color table
           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 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 map name from which to copy color table

           Path to rules file ("-" to read rules from stdin)


       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

       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
       category_value red_number:green_number:blue_number
       category_value red_number:green_number:blue_number
       category_value red_number:green_number:blue_number

       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
       percent_value% color_name
       percent_value% color_name
       percent_value% color_name

       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

       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

       To set the NULL (no data) color, use the "nv" parameter:
       0 black
       10% yellow
       nv white

       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


       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

       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


         d.colors,  d.colortable,  d.histogram,  d.legend,  r.colors.stddev,, r.univar,

       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.


       Michael Shapiro and David Johnson

       Last changed: $Date: 2013-02-15 14:04:18 -0800 (Fri, 15 Feb 2013) $

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