Patent ID: 8111004

Claim:
A memory comprising discrete color points and suitable for use with a color navigation system generating light with a variable color, the color points defined according to three-dimensional CIELAB coordinates hue (H), lightness (L), chroma (C), with predefined intervals ΔH between neighboring color points in the hue direction, with predefined intervals ΔL between neighboring color points in the lightness direction, and with predefined intervals ΔC between neighboring color points in the chroma direction, respectively; wherein ΔL is equidistant over the color space; and wherein ΔS is equidistant over the color space, with ΔC=ΔS·L, S indicating saturation; such that the perceptual color difference ΔE INV , defined according to the formula: Δ E INV =√{square root over ((Δ L ) 2 +( f C ( H )·Δ C ) 2 +(Δ H ) 2 )}{square root over ((Δ L ) 2 +( f C ( H )·Δ C ) 2 +(Δ H ) 2 )}{square root over ((Δ L ) 2 +( f C ( H )·Δ C ) 2 +(Δ H ) 2 )} is substantially constant over the color space for steps in the L direction and in the S direction; wherein f C (H) is a proportionality factor between 0 and 1 only depending on hue H; wherein, for hue values H between a first hue value (H 1 ) corresponding to red and a second hue value (H 2 ) corresponding to green, the proportionality factor f C (H) is equal to 1 and the number of color points in the hue direction in this range is equal to N H,RG ; wherein, for hue values between the second hue value (H 2 ) corresponding to green and a third hue value (H 3 ) corresponding to blue, the proportionality factor f C (H) is set to a constant value f GB such that the number N H,GB(fGB) of color points in the hue direction in this range differs less than 50% from N H,RG , N H,GB(fGB being equal to N H,RG ; wherein, for hue values between the third hue value (H 3 ) and the first hue value (H 1 ), the proportionality factor f C (H) is set to a constant value f BR such that the number N H,BR(fBR) of color points in the hue direction in this range differs less than 50% from N H,RG ; and wherein ΔH is a function of H such that, for steps in the hue direction along the border of the color space, said perceptual color difference ΔE INV is substantially constant.