The GMT package implements colour gradients with the cpt (colour palette) file format, and provides some tools for creating and manipulating them. The cptutils package contains a number of additional utilities, mostly for translation to and from other formats.
A wrapper script, gradient-convert, is included in the package to simplify the conversion process.
- cptcont make continuous cpt from discontinuous
- cptclip extract part of a cpt
- cptcat concatenate cpt files
- cpthsv modify RGB cpt gradient in HSV space
- cptinfo print summary information on a cpt file
- xycpt convert column data to cpt
GMT scale from GIMP's Sunrise
The cptutils package was written to aid the construction of the cpt archive cpt-city (where thousands of gradients can be downloaded). The Unix source distribution for version 1.56 (October 2014) of the package can be downloaded here (you will need to have libxml2 and libpng installed to compile it). Fedora Linux users will find a prebuilt package in their YUM repositories (or via RPM pbone, rpmfind) and Gentoo Portage is detailed here.
An online conversion tool which uses cptutils can be found at cptutils-online.