makecpt man page

makecpt — Make GMT color palette tables

Synopsis

makecpt [ -A[+]transparency ] [ -Ccpt ] [ -D[i|o] ] [ -E[nlevels] ] [ -F[R|r|h|c ][+c]] [ -Gzlo/zhi ] [ -I ] [ -M ] [ -N ] [ -Q[i|o] ] [ -Tz_min/z_max[/z_inc[+]] | -Tztable | -Tz1,z2,...,zn ] [ -V[level] ] [ -W ] [ -Z ]

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

Description

makecpt is a utility that will help you make static color palette tables (CPTs). You define an equidistant set of contour intervals or pass your own z-table or list, and create a new CPT based on an existing master (dynamic) CPT. The resulting CPT can be reversed relative to the master cpt, and can be made continuous or discrete. For color tables beyond the standard GMT offerings, visit cpt-city: http://soliton.vm.bytemark.co.uk/pub/cp….

The CPT 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 wherever values are undefined.

If the master CPT 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 gmt.conf 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. When there is no COLOR_MODEL entry in the master CPT, the COLOR_MODEL specified in the gmt.conf file or on the command line will be used.

Optional Arguments

-A[+]transparency
Sets a constant level of transparency (0-100) for all color slices. Prepend + to also affect the fore-, back-, and nan-colors [Default is no transparency, i.e., 0 (opaque)].
-Ccpt
Selects the master color table CPT 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 [Default gives a rainbow CPT]. Yet another option is to specify -Ccolor1,color2[,color3,...] to build a linear continuous cpt from those colors automatically. In this case colorn can be a r/g/b triplet, a color name, or an HTML hexadecimal color (e.g. #aabbcc ).
-D[i|o]
Select the back- and foreground colors to match the colors for lowest and highest z-values in the output CPT [Default uses the colors specified in the master file, or those defined by the parameters COLOR_BACKGROUND, COLOR_FOREGROUND, and COLOR_NAN]. Append i to match the colors for the lowest and highest values in the input (instead of the output) CPT.
-E[nlevels]
Implies reading data table(s) from given command-line files or standard input. We use the last data column to determine the data range; use -i to select another column, and use -bi if your data table is native binary. This z-range information is used instead of providing the -T option. We create a linear color table by dividing the table data z-range into nlevels equidistant slices. If nlevels is not given it defaults to the number of levels in the chosen CPT.
-F[R|r|h|c][+c]]
Force output CPT to written with r/g/b codes, gray-scale values or color name (R, default) or r/g/b codes only (r), or h-s-v codes (h), or c/m/y/k codes (c). Optionally or alternatively, append +c to write discrete palettes in categorical format.
-Gzlo/zhi
Truncate the incoming CPT so that the lowest and highest z-levels are to zlo and zhi. If one of these equal NaN then we leave that end of the CPT alone. The truncation takes place before any resampling.
-I
Reverses the sense of color progression in the master CPT. Also exchanges the foreground and background colors, including those specified by the parameters COLOR_BACKGROUND and COLOR_FOREGROUND.
-M
Overrule background, foreground, and NaN colors specified in the master CPT with the values of the parameters COLOR_BACKGROUND, COLOR_FOREGROUND, and COLOR_NAN specified in the gmt.conf file or on the command line. When combined with -D, only COLOR_NAN is considered.
-N
Do not write out the background, foreground, and NaN-color fields [Default will write them].
-Q[i|o]
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.
-Tz_min/z_max[/z_inc[+]] | -Tztable | -Tz1,z2,...,zn
Defines the range of the new CPT by giving the lowest and highest z-value and interval. Append /z_inc to sample the input CPT discretely at intervals z_inc between z_min and z_max; append a trailing + to interpret z_inc as the number of desired intervals instead. Alternatively, give the name of a ASCII file that has one z-value per record, or provide a list of comma-separated z-values instead If -T is not given, the existing range in the master CPT will be used intact.
-V[level] (more ...)
Select verbosity level [c].
-W
Do not interpolate the input color table but pick the output colors starting at the beginning of the color table, until colors for all intervals are assigned. This is particularly useful in combination with a categorical color table, like "categorical". Cannot be used in combination with -Z.
-Z
Creates a continuous CPT [Default is discontinuous, i.e., constant colors for each interval]. This option has no effect when no -T is used, or when using -Tz_min/z_max; in the first case the input CPT remains untouched, in the second case it is only scaled to match the range z_min/z_max.
-^ 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 exits.

Notes on Transparency

The PostScript language originally had no accommodation for transparency. However, Adobe added an extension that allows developers to encode some forms of transparency using the PostScript language model but it is only realized when converting the PostScript to PDF (and via PDF to any raster image format). GMT uses this model but there are some limitations: Transparency can only be controlled on a per-object or per-layer basis. This means that a color specifications (such as those in CPTs of given via command-line options) only apply to vector graphic items (i.e., text, lines, polygon fills) or to an entire layer (which could include items such as PostScript images). This limitation rules out any mechanism of controlling transparency in such images on a pixel level.

Color Hinges

Some of the GMT master dynamic CPTs are actually two separate CPTs meeting at a hinge. Usually, colors may change dramatically across the hinge, which is used to separate two different domains (e.g., land and ocean across the shoreline, for instance). CPTs with a hinge will have their two parts stretched to the required range separately, i.e., the bottom part up to the hinge will be stretched independently of the part from the hinge to the top, according to the prescribed new range. If the selected range does not include the hinge then no such partitioning takes place.

Color Aliasing

For best result when -T -Z is used we recommend you do no append a specific z_inc. This way the original CPT is used exactly as is but the z boundaries are adjusted to match the stated limits. Otherwise you may, depending on the nature of the input CPT, miss aspects of the color changes by aliasing the signal.

Examples

To make a CPT with z-values from -200 to 200, with discrete color changes every 25, and using a polar blue-white-red colortable:

gmt makecpt -Cpolar -T-200/200/25 > colors.cpt

To make an equidistant CPT from z = -2 to 6 using the continuous default rainbow of colors:

gmt makecpt -T-2/6 -Z > rainbow.cpt

To use the GEBCO look-alike CPT with its default range for bathymetry, run

gmt makecpt -Cgebco > my_gebco.cpt

or simply use -Cgebco directly in the application that needs the color table. To create a 24-level rainbow color table suitable for plotting the depths in the data table depths.txt (with lon, lat, depths), run

gmt makecpt -Cgebco depths.txt -i2 -Z -E24 > my_depths.cpt

To make a custom discrete color table for depth of seismicity, using red color for hypocenters between 0 and 100 km, green for 100-300 km, and blue for deep (300-1000 km) earthquakes, use

gmt makecpt -Cred,green,blue -T0,80,300,1000 -N > seis.cpt

Finally, to make a continuous CPT from white to blue as z goes from 3 to 10, try

gmt makecpt -Cwhite,blue -T3,10 -Z > cold.cpt

Bugs

Since makecpt will also interpolate from any existing CPT you may have in your directory, you should not use one of the listed cpt names as an output filename; hence the my_gebco.cpt in the example. If you do create a CPT of such a name, e.g., rainbow.cpt, then makecpt will read that file first and not look for the master CPT in the shared GMT directory.

See Also

gmt, grd2cpt

Referenced By

cptcat(1), cptclip(1).

October 20, 2016 5.3.1 GMT