cpt-city

GMT colour palette tables

• The format is described in Section 4.15 of the GMT Technical Reference and Cookbook.
• Manual page for the GMT programs makecpt and grdcpt.
• The cptutils package provides some extra tools for manipulating cpt files.
• The standard GMT palettes are shown in this Appendix to the Technical Reference. See also Thorsten W. Becker's single-page PDF file.

GIMP gradients

• The GIMP is an open-source drawing application with a fine gradient editor and a selection of built-in gradients, available in translation here.
• The gradient format is discussed in this thread on the gimp-developer mailing list.
• The open-source SpectraG program generates GIMP gradients.

SVG gradients

• The W3C has defined an XML-based gradient format as a part the SVG vector graphics format.
• The open clipart library contains a number of SVG gradients (translated here).

POV-Ray colour maps

• The free ray-tracing program POV-Ray supports colour-maps as part of its complex pigment type.
• The online documentation for version 3.6.1 describes the syntax and has several coding examples.

Cinema 4D

• The gradients from cpt-city can be imported into the Cinema 4D package using the gimp-gradient plugin by Ian Gorse.

Paint Shop Pro

• Paint Shop Pro, uses version 3 of the grd format for its gradients. Typically the files have the extensions .PspGradient or .jgd.
• The format is undocumented but rather simple: a reverse-engineered technical description can be found here.

Photoshop

• Photoshop uses various versions of the of the grd format, and can read the version 3 files on cpt-city. This amusing thread on usenet discusses the later versions.
• Matt Schraeder (heroically) converted the complete set of grd version 3 gradients on cpt-city to a single Photoshop gradient; his adventures are documented in his frozen solid blog.

GRASS

• Users of the GRASS GIS system can import the cpt files on cpt-city using the r.cpt2grass script from the GRASS Add-ons collection.
• Information on the use of colour maps in GRASS can found on Hamish Bowman's Peripheral Visionary pages.

Medcon

• The open-source medical image viewer medcon uses a simple 256 level lookup table (LUT) for its colour gradients.
• The GIMP gradients on cpt-city can be converted to the LUT format with the gimplut program, part of the cptutils package

Gradients and colour schemes in general

• Cynthia A. Brewer, Associate Professor at the Department of Geography of Pennsylvania State University has made studies in map design, colour theory applications in cartography, hypothesis generation in visualisation and choropleth classification for maps in series. She is an author of the wonderful ColorBrewer site whose schemes are available in cpt translation here.
• The uses of gradients in photographic toning and colour-mapping are the subject of Piecrust Design's toned.
• Shaded relief is a method for representing topography on maps in a natural, aesthetic, and intuitive manner. At the reliefshading.com site one can find rules and guidelines for the design and production of shaded relief, an overview of its history, examples produced by professional relief artists, technical tips, and much more. See also Tom Patterson's site, shadedrelief.com.
• Jim Mossman gives an interesting perspective on shading in cartography in a series of articles on his ShadeMax palettes: Parts 1, 2 and 3.
• The Department of Geography at the University of Oregon has an interesting site on data graphics, including several carefully chosen colour scales.