viridis

Viridis is a perceptually uniform sequential colormap used in data visualization. It encodes numeric values as colors along a gradient that generally transitions from dark blue through green to yellow. The design emphasizes a smooth progression in brightness and hue so that equal steps in data produce roughly equal perceptual changes, and it remains distinguishable when reproduced in grayscale or on color-impaired displays.

The colormap was created by Nathaniel Smith and Stefan van der Walt and has become widely adopted in scientific plotting libraries, notably in Matplotlib and related tools. It is commonly used for heatmaps, surface plots, and image displays because of its readability across a broad range of data, including values near the extremes. Viridis is part of a family of colormaps that share the same perceptual goals, offering alternative color schemes such as magma, inferno, plasma, and, in addition, cividis, which is tailored for color vision deficiency.

Key design goals of viridis include perceptual uniformity, good contrast across the data range, and consistent performance across different output devices and viewing conditions. The palette is also designed to reproduce well in grayscale, facilitating interpretation when color is not available.

Etymology: viridis is Latin for green, reflecting the characteristic green-leaning portion of the gradient, though the palette spans from cool blues to warm yellows. The term has become a standard reference in discussions of modern, accessibility-conscious color visualization.