qualpal

What qualpal is

Qualpal is a free C++ library for creating qualitative color palettes with an emphasis on perceptual distinction, particularly for data visualization. It can use RGB colors, HSL or LCHab color spaces, or predefined palettes as inputs. You can set a background color to help keep generated colors distinct from it, or extend a palette while preserving specified colors. Its palette-selection heuristic uses farthest-point sampling and describes the results as approximately maximally distinct. Qualpal can also simulate deuteranomaly, protanomaly, and tritanomaly using the Machado et al. model. It includes a command-line interface for palette generation and analysis, along with a browser-based palette generator; the web version has more limited functionality than the library and R package. The project also provides the qualpalr R package and lists a Python package. Building from source requires CMake 3.15 or later and a C++17-compatible compiler; OpenMP is optional for parallelization. Qualpal does not choose colors based on aesthetic factors such as harmony or complementary relationships, and the source repository lists the MIT License.