OSA-UCS

The committee decided that, in order to accurately represent uniform color differences in each direction, a new shape of three dimensional Cartesian geometry would need to be used.

Immediately following this discovery, work began to create a space that would behave uniformly in all directions of color difference.

[2] From the data collected, formulas were developed and parameters were defined to create the new uniform color space.

They chose the reference 10 degree observer and Illuminant D65 to characterize the uniform space and a neutral gray background of 30% reflectance.

The last step to completing this geometry was in a rescaling of the vertical L axis, in order to achieve integer coordinate locations for color description.

First, a factor representing the Helmholtz-Kohlrausch effect must be calculated from the x and y chromaticity coordinates: Next determine the modified luminous reflectance: Then calculate the lightness and chroma modification factor: Convert the XYZ values to RGB using the linear matrix transformation: Last, calculate a and b: and multiply them by C to obtain OSA-UCS g and j: Although no closed-form conversion from OSA-UCS to CIEXYZ exists, numerical solvers have been written, including one based on the Newton–Raphson method[5][6] and another based on an artificial neural network.