In computer graphics, a color gradient specifies a range of position-dependent colors, usually used to fill a region. For example, many window managers allow the screen background to be specified as a gradient. The colors produced by a gradient vary continuously with position, producing smooth color transitions. A color gradient is also known as a color ramp or a color progression. In assigning colors to a set of values, a gradient is a continuous colormap, a type of color scheme.
Definitions
Color gradient is a set of colors arranged in a linear order
A continuous colormap is a curve through a colorspace
An axial color gradient is specified by two points, and a color at each point. The colors along the line through those points are calculated using linear interpolation, then extended perpendicular to that line. In digital imaging systems, colors are typically interpolated in an RGB color space, often using gamma compressedRGB color values, as opposed to linear. CSS and SVG both support linear gradients.
Radial gradients
A radial gradient is specified as a circle that has one color at the edge and another at the center. Colors are calculated by linear interpolation based on distance from the center. This can be used to approximate the diffuse reflection of light from a point source by a sphere. Both CSS and SVG support radial gradients.
Conic gradients
Conic or conical gradients are gradients with color transitions rotated around a center point. Example conic gradients include pie charts and color wheels.
The appearance of a gradient not only varies by the color themselves, but also by the color space the calculation is performed in. The problem usually becomes important for two reasons:
Gamma correction to a color space. With a typical γ of around 2, it is easy to see that a gamma-enabled color space will blend darker than a linear-intensity color space, since the sum of squares of two numbers is never more than the square of their sum. The effect is most apparent in blending complementary colors like red and green, with the middle color being a dark color instead of the expected yellow.
Handling of other perceptual properties. In information visualization, it is undesirable to have a supposedly "flat" gradient show non-monotonic variations in lightness and saturation along the way. This is because human vision emphasizes these qualities, causing bias or confusion in interpretation.
Examples
HSV rainbow
Tools
The CCC-Tool is a general tool for the creation, analyzing and testing of colormaps with the effort to minimize the needed interaction components.
an online tool to enable you to mathematically analyze the properties of a colormap in multiple color spaces
