Abstract-A red/green equilibrium light is one which appears neither reddish nor greenish (i.e. either uniquely yellow, uniquely blue, or achromatic). A subset of spectral and nonspectral red/green equilibria was determined for several luminance levels, in order to test whether the set of all such equilibria is closed under linear color-mixture operations.The spectral loci ofequilibrium yellow and blue showedeither no variation or visually insignificant variation over a range of l-2 log,, unit. There were no trends that were repeatable across observers. We concluded that spectral red/green equilibria are closed under scalar multiplication; consequently they are invariant hues relative to the Bezold-Briicke shift.The additive mixture of yellow and blue equilibrium wavelengths, in any luminance ratio, is also an equilibrium light. Small changes of the yellowish component of a mixture toward redness or greeness must be compensated by predictable changes of the bluish component of the mixture toward greenness or redness. We concluded that yellow and blue equilibria are complementary relative to an equilibrium white; that desaturation of a yellow or blue equilibrium light with such a white produces no Abney hue shift; and that the set of red/green equilibria is closed under general linear operations. One consequence is that the red/green chromatic-response function, measured by the Jameson-Hurvich technique of cancellation to equilibrium, is a linear function of the individual's color-matching coordinates. A second consequence of linear closure of equilibria is a strong constraint on the class of combination rules by which receptor outputs are recoded into the red/green opponent process.

Abstract-A yellow/blue equilibrium Iight is one which appears neither yellowish nor bluish (i.e. uniquely red, uniquely green, or achromatic). The spectral locus of the monochromatic greenish equilibrium (around 500 nm) shows little, if any, variation over a luminance range of .! log,, units. Reddish equilibria are extraspectral. involving mixtures of short-and long-wave light. Their wavelength composition is noninvariant with luminance: a reddish equilibrium light turns bluish-red if luminance is increased with wavelength composition constant.The additive mixture of the reddish and greenish equilibria is again a yellow, blue equilibrium light.We conclude that yellow/blue equilibrium can be described as the zeroing of a nonlinear functional.which is, however, approximately linear in the short-wavelength ("blue") and middle-wavelength ("green") cone responsesand nonlinear only in the long-wavelength ("red") cone response. The "red" cones contribute to yellowness but via a compressive function of luminance. This effect works against the direction of the Bezold-Briicke hue shift. The Jameson-Hurvich yellowiblue chromatic-response function is only approximately correct; the relative values of yellow/blue chromatic response for an equal energy spectrum must vary somewhat with the energy level.

This paper reviews recent human factors research studies conducted in the Aerospace Human Factors Research Division at NASA Ames Research Center related to the development and usage of Enhanced or Synthetic Vision Systems. Research discussed includes studies of field of view (FOV), representational differences of infrared (IR) imagery, head-up display (HUD) symbology, HUD advanced concept designs, sensor fusion, and sensor/database fusion and evaluation. Implications for the design and usage of Enhanced or Synthetic Vision Systems are discussed.

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