HSI

HSI stands for Hue-Saturation-Intensity, a color model used in image processing and computer vision. It represents colors by separating chromatic information from brightness, offering a way to describe color that aligns more closely with human perception than the RGB color model. In HSI, hue encodes the type of color, saturation measures color vividness, and intensity (or brightness) captures the overall lightness of the color.

In typical HSI representations, hue is defined as an angle on a circular color wheel (often 0 to 360 degrees), while saturation and intensity range from 0 to 1 or 0 to 100%. Hue is undefined for colors that are gray (where R, G, and B are equal). Intensity is intended to reflect perceived brightness, independent of chromatic purity, and saturation indicates how far a color is from gray.

Conversion from RGB to HSI involves first normalizing the RGB values, then computing I as the average of the three channels, S as a function of how far the color is from gray (often using the minimum RGB value and the sum), and Hue from the relative differences among the channels. The exact formulas can vary by implementation. Because HSI is nonlinear and not perceptually uniform, exact conversions can differ between systems, and hue can be unstable near grayscale.

Applications of HSI include color-based segmentation, feature extraction, and lighting-robust image analysis. It is often contrasted with HSV and HSL, which use different definitions of brightness. In other contexts, HSI may also stand for Human System Integration, a field focusing on human interaction with complex systems.