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MAKECPT(1) Generic Mapping Tools MAKECPT(1)

makecpt - Make GMT color palette tables

makecpt [ -Ctable ] [ -D ] [ -I ] [ -M ] [ -N ] [ -Q[i|o] ] [ -Tz0/z1/dz | -T ztable ] [ -V ] [ -Z ]

makecpt is a utility that will help you make color palette tables (cpt files). You define an equidistant set of contour intervals or pass your own z-table, and create a new cpt file based on an existing master cpt file. The resulting cpt file can be reversed relative to the master cpt, and can be made continuous or discrete.
The color palette includes three additional colors beyond the range of z-values. These are the background color (B) assigned to values lower than the lowest z-value, the foreground color (F) assigned to values higher than the highest z-value, and the NaN color (N) painted whereever values are undefined.
If the master cpt file includes B, F, and N entries, these will be copied into the new master file. If not, the parameters COLOR_BACKGROUND, COLOR_FOREGROUND, and COLOR_NAN from the .gmtdefaults4 file or the command line will be used. This default behavior can be overruled using the options -D, -M or -N.
The color model (RGB, HSV or CMYK) of the palette created by makecpt will be the same as specified in the header of the master cpt file. When there is no COLOR_MODEL entry in the master cpt file, the COLOR_MODEL specified in the .gmtdefaults4 file or on the command line will be used.

Selects the master color table table to use in the interpolation. Choose among the built-in tables (type makecpt to see the list) or give the name of an existing cpt file [Default gives a rainbow cpt file].
Select the colors for lowest and highest z-values in the output cpt file as the back- and foreground colors that will be written to the cpt file [Default uses the colors specified in the master file, or those defined by the parameters COLOR_BACKGROUND, COLOR_FOREGROUND, and COLOR_NAN].
Reverses the sense of color progression in the master cpt file. Also exchanges the foreground and background colors, including those specified by the parameters COLOR_BACKGROUND and COLOR_FOREGROUND.
Overrule background, foreground, and NaN colors specified in the master cpt file with the values of the parameters COLOR_BACKGROUND, COLOR_FOREGROUND, and COLOR_NAN specified in the .gmtdefaults4 file or on the command line. When combined with -D, only COLOR_NAN is considered.
Do not write out the background, foreground, and NaN-color fields [Default will write them].
Selects a logarithmic interpolation scheme [Default is linear]. -Qi expects input z-values to be log10(z), assigns colors, and writes out z [Default]. -Qo takes log10(z) first, assigns colors, and writes out z.
Defines the range of the new cpt file by giving the lowest and highest z-value and the interval. Alternatively, give the name of a ASCII file that has one z-value per record. If not given, the existing range in the master cpt file will be used intact.
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
Creates a continuous cpt file [Default is discontinuous, i.e., constant colors for each interval].

To make a cpt file with z-values from -200 to 200, with discrete color changes every 25, and using a polar blue-white-red colortable:
makecpt -Cpolar -T-200/200/25 > colors.cpt
To make an equidistant cpt file from z = -2 to 6, in steps of 1, using continuous default rainbow colors:
makecpt -T-2/6/1 -Z > rainbow.cpt
To make a GEBCO look-alike cpt file for bathymetry, run
makecpt -C gebco > my_gebco.cpt

Since makecpt will also interpolate from any existing .cpt file you may have in your directory, you cannot use one of the listed cpt names as an output filename; hence the my_gebco.cpt in the example.

GMT(1), grd2cpt(1)
1 July 2018 GMT 4.5.18

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