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grd2rgb - Write r/g/b grid files from a grid file, a raw RGB file, or SUN rasterfile


grd2rgb infile template [ cpt ] [ xinc[m|s][/yinc[m|s]] ] [ layer ] region [level] [
width/height[/n_bytes] ] [ -r ]

Note: No space is allowed between the option flag and the associated arguments.


grd2rgb reads one of three types of input files: (1) A Sun 8-, 24-, or 32-bit raster file;
we the write out the red, green, and blue components (0-255 range) to separate grid files.
Since the raster file header is limited you may use the -R, -I, -r options to set a
complete header record [Default is simply based on the number of rows and columns]. (2) A
binary 2-D grid file; we then convert the z-values to red, green, blue via the provided
CPT file. Optionally, only write out one of the r, g, b, layers. (3) A RGB or RGBA raw
raster file. Since raw rasterfiles have no header, you have to give the image dimensions
via the -W option.


infile The (1) Sun raster file, (2) 2-D binary grid file, or (3) raw raster file to be

Provide an output name template for the three output grids. The template should be
a regular grid file name except it must contain the string %c which on output will
be replaced by r, g, or b.


-Ccpt name of the color palette table (for 2-D binary input grid only).

x_inc [and optionally y_inc] is the grid spacing. Optionally, append a suffix
modifier. Geographical (degrees) coordinates: Append m to indicate arc minutes or s
to indicate arc seconds. If one of the units e, f, k, M, n or u is appended
instead, the increment is assumed to be given in meter, foot, km, Mile, nautical
mile or US survey foot, respectively, and will be converted to the equivalent
degrees longitude at the middle latitude of the region (the conversion depends on
PROJ_ELLIPSOID). If /y_inc is given but set to 0 it will be reset equal to x_inc;
otherwise it will be converted to degrees latitude. All coordinates: If = is
appended then the corresponding max x (east) or y (north) may be slightly adjusted
to fit exactly the given increment [by default the increment may be adjusted
slightly to fit the given domain]. Finally, instead of giving an increment you may
specify the number of nodes desired by appending + to the supplied integer
argument; the increment is then recalculated from the number of nodes and the
domain. The resulting increment value depends on whether you have selected a
gridline-registered or pixel-registered grid; see App-file-formats for details.
Note: if -Rgrdfile is used then the grid spacing has already been initialized; use
-I to override the values.

Output only the specified layer (r, g, or b). [Default outputs all 3 layers].

-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest.

-V[level] (more ...)
Select verbosity level [c].

Sets the size of the raw raster file. By default an RGB file (which has 3
bytes/pixel) is assumed. For RGBA files use n_bytes = 4. Use -W for guessing the
image size of a RGB raw file, and -W=/=/4 if the raw image is of the RGBA type.
Notice that this might be a bit slow because the guessing algorithm makes uses of

-r (more ...)
Set pixel node registration [gridline].

-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows
use just -).

-+ or just +
Print an extensive usage (help) message, including the explanation of any
module-specific option (but not the GMT common options), then exits.

-? or no arguments
Print a complete usage (help) message, including the explanation of options, then

Print GMT version and exit.

Print full path to GMT share directory and exit.


To use the color palette topo.cpt to create r, g, b component grids from hawaii_grv.nc
file, use

gmt grd2rgb hawaii_grv.nc -Ctopo.cpt -Ghawaii_grv_%c.nc

To output the red component from the Sun raster radiation.ras file, use

gmt grd2rgb radiation.ras -Lr -Gcomp_%c.nc

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