CIELABiin

CIELABiin is a hypothetical extension of the CIELAB color space proposed to include an illumination-invariant dimension alongside the standard L*, a*, and b* coordinates. Unlike the conventional space, which maps colors to perceptual coordinates under a fixed reference illuminant, CIELABiin adds a fourth coordinate i that encodes how a color's appearance is expected to persist across changes in lighting and viewing angle. The four coordinates are L*, a*, b*, and i, with L*, a*, and b* defined as in CIELAB, and i defined by an empirical or learned model calibrated from reflectance and illumination data. In practice, i is constrained to the range [0,1], where higher values indicate greater invariance to illumination variation.

The transformation to CIELABiin combines the standard CIELAB transformation from XYZ with a separate estimation of i. A typical approach uses scene illuminant estimation or known lighting conditions to feed a model that predicts i from L*, a*, b*, and estimated illumination. The result is a four-dimensional representation intended to improve cross-lighting color comparison and grading tasks.

Applications for CIELABiin are mostly in theoretical color science, digital archiving, and color-critical workflows where consistent appearance across lighting is desired but not guaranteed by existing spaces. However, CIELABiin is not an official standard, lacks universal adoption, and its interpretation depends on the chosen model for i and the reliability of illuminant estimation.

See also: CIELAB, CIE color spaces, color appearance models.