makecpt(1) GMT makecpt(1)
NAME
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[c][z] ] [ -M ] [ -N ] [
-Q[i|o] ] [ -Tz_min/z_max[/z_inc[+]] | -Tztable | -Tz1,z2,^<i>a|,zn ] [
-V[level] ] [ -W[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 exist-
ing 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/cpt-city/.
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 speci-
fied in the gmt.conf file or on the command line will be used.
REQUIRED ARGUMENTS
None.
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-col-
ors [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,a|] 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 equidis-
tant 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-lev-
els 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. See also manipulating_CPTs
-I[c][z]
Append c [Default] to reverse the sense of color progression in
the master CPT. Also exchanges the foreground and background
colors, including those specified by the parameters COLOR_BACK-
GROUND and COLOR_FOREGROUND. Append z to reverse the sign of
z-values in the color table. Note that this change of z-direc-
tion happens before -G and -T values are used so the latter much
be compatible with the changed z-range. See also manipulat-
ing_CPTs
-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 col-
ors, and writes out z.
-Tz_min/z_max[/z_inc[+]] | -Tztable | -Tz1,z2,^<i>a|,zn
Defines the range of the new CPT by giving the lowest and high-
est 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 a|)
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 col-
ors for all intervals are assigned. This is particularly useful
in combination with a categorical color table, like acategori-
cala. Cannot be used in combination with -Z. Alternatively, use
-Ww to produce a wrapped (cyclic) color table that endlessly
repeats its range.
-Z Creates a continuous CPT [Default is discontinuous, i.e., con-
stant 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 just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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 all options, then exits.
NOTES ON TRANSPARENCY
The PostScript language originally had no accommodation for trans-
parency. 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 spe-
cific 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 use the gebco color table but reverse the z-values so it can be used
for positive depth values, try
gmt makecpt -Cgebco -Iz > my_positive_gebco.cpt
To create a 24-level rainbow color table suitable for plotting the
depths in the data table depths.txt (with lon, lat, depths), run
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
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
To make a wrapped (cyclic) CPT from the jet table over the interval 0
to 500, i.e., the color will be wrapped every 500 z-units so that we
always get a color regardless of the z value, try
gmt makecpt -Cjet -T0/500 -Ww > wrapped.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 cre-
ate 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(1), grd2cpt(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 makecpt(1)
gmt5 5.4.2 - Generated Thu Jun 29 14:04:43 CDT 2017