OSA Atlas

This program presents different plane sections of the OSA-UCS space. The color samples are lit by the D65 illuminant. Empty rectangles represent color not reproducible by the monitor used.
The observer is the CIE 1964.
The section planes different from those at constant lightness are partially overlapping showing simultaneous luminance and chromatic contrast.


The system with uniform perceived color scales of the American Society of Optics (OSA), known as OSA-UCS {OSA-uniform color scales}, is a system base on the color appearance perceived by the observer CIE 1964, and was realized by ceramic tiles ordered in a three dimensional equispaced lattice.
The illuminant used iis the D65 and the color samples must be seen over a neutral ground with a percentage luminance factor equal to 30. The crispening effect is considered by this system. The color samples as ordered according to a three dimensional cube-octahedron lattice with the aim to have contiguous color samples at distances measured by equal jnd numbers.

  • The three-dimensional lattice is constituted by a set of parallel planes with square lattices, and the cells of contiguous planes are mutually translated in order to have the corners in the centers of the cells of the continuous planes. Consequently, any color sample is in the center of a three dimensional cell constituted by 12 samples. These planes are classified by using the lightness LOSA, defined taking into accountthe Helmholtz-Kohlrausch effect, that shows that the brightness depends on the luminance and on the chromaticity
  • the crispening, that says that the brightness of a color sample depends on the brightness of the surround, i.e. samples with lower brightness appear darker and with higher brightness lighter.
The lightness of this system is defined as

where C = 0.042 (Y0 - 30)1/3is a contribution that considers the crispening, Y0 = Y10 F where Y10 is the percentage luminance factor of the color sample and
F = 4.4934x102 +4.3034 y102-4.376 x10 y10-1.3744 x10- 2.56439 y10+1.8103), considers the Helmholtz-Kohlrausch effect.

The constant luminance planes are spanned by two Cartesian coordinates (g, j), g from English “green” and j from French “jeune”, for denoting two hues proper of the color opponencies: green-red opponency is specified by coordinate g and blue-yellow by j. Globally, the coordinates (LOSA, g, j) correspond to three axes, two of which correspond to the Hering’s opponency mechanisms.
The physical color samples of this system have coordinates belonging to these intervals: